# Injected Diesel 56cc 2 Stroke, Will it ever work?"



## Lloyd-ss (Mar 14, 2019)

Hello everyone.
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This thread actually started a few days ago on the general engine discussion forum, but it seemed like it really belonged on this forum, so here it is.
https://www.homemodelenginemachinis...smatched-rings-and-piston-and-cyl-bore.31104/
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I have wanted to build a diesel for a long time, actually a 2 stroke complete with Roots blower. Why not bite off more than I can chew? I call it being greedy; and it usually gets me in trouble. EDIT:I have since revised my expectations and have dropped the blower and 2 stroke concept.
About a year ago, I found Find Hansen's beautiful engines on Youtube, and that almost pushed me into the project. Then I ran across his new video of the build of an A-Frame diesel. Darn! Then I found this great forum with lots of smart and helpful and friendly members. That's a rare combination to find on the internet! So I dove in head first.

The selection of 33mm bore x 66mm bore had an odd beginning. In one of my junk piles I had some short pieces of 8" welded steel pipe (actually 8-5/8" O.D.). I thought, that could make a great flywheel, what size cylinder would it go with?

So the first item is the one that for me, took the least amount of decision making. Like using 4 spokes or 5 spokes? The 5 curved spokes spoke to me. It is bolted construction, with inner and outer rim, 5 spokes and a hub, and hidden bolts.

I started by slicing off 3 pieces of the 8-5/8" O.D. x .30 wall welded steel pipe: rim, inner rim, spokes. I used a Harbor Freight $120 portable band/hack saw and had to saw all the way the way around each ring. I sawed them all in one session, using plenty of oil on the cuts. The Lennox blade held up fine. The saw didn't whimper. 

My lathe is a Grizzly 10x22 and that pipe definitely pushed the limit, but I got the outer rim roughed out, clamping from the inside out with the 6-1/4" 4 jaw. Indicating the rings in to get them to run optimally for least amount of material removal was a chore. The outer ring was the first part rough machined. To make the inner spoke ring, I sawed out a 2" section of one of the pipe slices, and clamped it to force it into an 8" O.D.  Then I welded it, multiple passes, grinding out the flux and inclusions between passes, One thing that really helped the welding was preheating the joint area with a Mapp gas torch. Welding that 5/16" wall just wouldn't have worked, not a my skill level anyway. Then I rough machined the new not trying to get 100% cleanup.
I machined the last ring to the finished cross section of the spokes.
The hub was rough turned from 12L14. It has an O.D. groove the width of the spokes, and has 5 flats machined into that groove.
I rough cut the 5 spokes to length plus about 1/8". It is bolted construction, with each spoke attached to the rim with a single 8-32 bolt, with the head counterbored into the rim. After all 5 spokes were attached to the rim, I fit them to the hub and determined how to trim the ends of the spokes and install the bolts.

After it was all lightly bolted together I chucked it in the lathe and pushed it around to get minimal runout and wobble, which ended up being about 30 thou. I tightened the bolts up, using a generous amount of 680 loctite. I then trued it up ont he lathe, changing the chucking at least 4 times.

Then the outer rim was attached using (5) 10-32 set screws that fit into pockets on the I.D. of the outer rim. After it had a final alignment, one last set of clean-up cuts were needed to get the non-painted surfaces all pretty looking. Lastly was several sessions of epoxy and JB Water Weld. I was shocked at how well that combination worked. i cleaned with acetone, and lightly preheated before applying epoxy, and used a heat gun to get the epoxy to flow properly. If this wheel were dropped hard enough to break it, I think a cast iron one would have broken too.

Here are the final as-built specs for the flywheel.
Outer rim O.D. 8.58"
Outer Rim width 1.99"
Inner rim 1.13 wide x . 25 thick
Spokes (5) at .88" x .20" cross section
Hub 2.30 long x 1.82 O.D.
Hub Bore .75"
Weight 7.96 pounds

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Starting with a chunk of 8" nominal welded steel pipe.






Three slices of pipe.





 L to R, Outer rim, spokes, inner rim.




The bolted assembly with the epoxy and  bolts visible.
The JB water weld has NOT been applied yet.
EDIT: Each spoke is machined for a snug fit into its loacation, including a snug fit into the matching groove in the hub. There is one 8-32 bolt radially thru the inner rim into the spoke. There is also a 10-32 bolt that goes thru the spoke radially into the hub.When these 10 screws were all tightened and secured with Loctite 680, the flywheel became a rigid unit. The outer rim was a slip fit onto the inner rim, and epoxy was was used to secure it in place (and possibly kill some vibration) and was also secured with setscrews radially outward from the inner rim into pockets in the outer rim. This method allowed the outer rim to be aligned with the hub to minimized radial and axial runout. The additional epozy and JB water weld fillets are mainly for cosmetic purposes, but I am sure they also will contribute to strength and vibration damping.





After filling, sanding, priming and painting, here is the Glamour photo
of the finished flywheel,  using special lighting,
and the photo editor, for those extra special high-lites, LOL.





More to come, but not really fast.
Lloyd


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## minh-thanh (Mar 15, 2019)

Nice flywheel ! I really like a diesel, hope you will succeed .


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## Lloyd-ss (Mar 15, 2019)

Thank you minh-thanh. I have been cautioned  about the difficulty of injected diesel, but if it doesn't run,  it wont be because i didn't give it my best shot.
Lloyd


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## Johno1958 (Mar 15, 2019)

Good luck with it Lloyd.


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## Lloyd-ss (Mar 15, 2019)

Johno1958 said:


> Good luck with it Lloyd.



Thanks Johno, I am sure I'll need a fair helping of luck along the way.
I am working on the injector prototype right now. Started the design with a pintle that opens outward, but am now seriously considering making one that opens inward. They seem inherently safer (I think). With the open outward, if the tapered head broke off into the combustion chamber there would be a serious disaster . With the open inward style of pintle, at least there is no head to break off.


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## Lloyd-ss (Mar 17, 2019)

I made a few of the parts for the injector. The plan is to get it built and tested before making any of the other parts for the engine.


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## George Punter (Mar 18, 2019)

Lloyd I was interested to read this thread and see your photographs of the progress on your Diesel engine. About six years ago I followed the same path and for the same reasons. I had drawings for the 6/1 Lister Diesel engine and used these to make a scale model.  The engine is 20cc and uses direct infection into a pre combustion chamber. I used a modified gass jet as the injection nozzle and the injection pump had a bore of 4mm and a stroke of 1mm. A manual bypass was used to pass the excess fuel. The injector fuel line had check valves to prevent fuel coming back down the line. I am very much a " a try it and see if it works" type of model engineer and don't get bogged down with too much theory, but there was some discussion relating to it not being a "real" diesel. In my book if there was no spark plug to ignite the mixture so it was a Diesel engine. I have included some photographs of this engine and should you want to see it working it is on U tube  - just type in model lister Diesel engine. Good luck with your project and I will continue to follow your progress.
George.


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## Lloyd-ss (Mar 18, 2019)

George, nice engine and video, too. Funny about the discussion on whether or not its a "real" diesel. Looks like one to me, too. Gotta keep a sense of humor and have fun, and in the video it looked like you were having fun.
Whenever I watch one of these model engine videos, especially the diesels, I realize how many questions there are that I didn't even know I was supposed to have. Wow! I usually rough out an entire design or concept, and then detail the drawings as I go, but most importantly, I try and be really good about cleaning up my cadd design with as-built drawings as I make each individual part. This engine is based very loosely on what one of Find Hansens horizontals look like, but i am doing my own drawings and design, and when I am done, it will be quite different. 
On the unanswered questions, I am wondering about the 33x66mm (56cc) size.  Maybe that's too big, IDK.
Cooling. It will have a water jacket, but I watched a video the other day (dieselpilot directed me to it) where the builder had a little bitty radiator with his engine. Hmmmm.
Lube systems. Seems like bronze bushings and bearings with drip lubrication are popular.  What about needle bearings or something that doesn't need to be oiled? BTW, I am not trying to keep this authentic to any period or design, I just want it to work and run, and look kinda cool, too.
Glow plugs. Anybody ever use a glow plug for starting? Real diesels do. The airplane engine glow plugs continue to stay hot after the electricity is cut off due to the reaction with the nitromethane  fuel, but I don't know if they would do that running diesel. I would only want it for starting, definitely not for running.

A real can of worms, but already a lot of fun, and I definitely like meeting all of the Forum members. That doubles the fun and probably cuts the mistakes in half, LOL.
Lloyd


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## Lloyd-ss (Mar 18, 2019)

I finished making all of the parts for the injector, and next will be the final assembly of it, and then testing it for functionality. 
I hope it works, LOL.

Here's how its "supposed" to operate.
There will be constant low pressure from a pump on the engine to keep approx 50psi (TBD) of pressure on the fuel in the injector. There will be a check ball in the fuel line near the injector to protect the pump during actual injection. The injector has a .062 dia piston at the top, that will be operated by a rocker arm that adjustable via a governor to control the stroke length. Stroke length could be a long as .115".  The .062 dia keeps the force to operate the piston low  ( less than 5 pounds force) but still be able to produce over 1,000 psi. The piston is hydraulicly coupled to the pintle; the pintle does not open by mechanical force, just by the pulse in hydraulic pressure. (I am hoping there isn't too much "give" in the hydraulic system and that the pintle does indeed open crisply. The return spring on the pintle holds it closed until the opening pressure (TBD) is exceeded by the hydraulic pressure from the rocker driven 1/16" dia piston. The travel of the pintle is limited by the two locknuts to about .005" (TBD) so that the pintle doesn't just blow open and dump all the fuel at once. The plan is for the fuel to atomize better thru the barely-open pintle.  
There are 2 high pressure ferrule compression fittings on the valve body. One is the fuel supply, and the other is to attach a pressure gauge during testing. I will probably have to do something to protect the test gauge if I run the injector at speed. After testing, the extra port will be sealed off with a 10-32 seal screw.
One thing I like about this design is that there is only one dynamic O-ring seal in the injector. All the other o-rings are static seals. Of course, there is always the pintle which probably won't seal the first time. Sigh.

That's the plan, anyway. You can learn a lot from failed tests. right?
Lloyd.


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## J.Bueno (Mar 19, 2019)

Hi. Great job. This is my first participation in HMEN. I'm building a diesel engine too. I'm limited in tools. I only have lathe.
 I have already obtained good results in the high pressure pump  and the injector through a method similar to this one. 
Initially, I started using the oring for sealing the connections but gave undesirable elasticity in the hydraulic system, then replace them with paper joints.
Glad to see your project.

 I'll be following up.


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## Lloyd-ss (Mar 19, 2019)

J. Bueno, thanks for your comment. Good luck on your project too.
Lloyd


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## werowance (Mar 20, 2019)

Curious about the part that looks like a spring.  is it a spring?  if so what material did you make it from? it appears to have been wound with some sort of flat stock or shim stock.


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## Lloyd-ss (Mar 20, 2019)

werowance said:


> Curious about the part that looks like a spring.  is it a spring?  if so what material did you make it from? it appears to have been wound with some sort of flat stock or shim stock.



It is indeed a spring, home-made. I needed a very stiff, but compact spring, to hold the pintle closed, similar to what you might find in a regulator bonnet. There was nothing suitable in my collection, but I did have some straight lengths of .041 dia stainless steel spring wire.  I clamped one end of a 5/64 allen wrench (to serve as a mandrel), together with one end of the 12" piece of spring wire.  Then I just manually wrapped the wire around the mandrel, keeping the spacing as nice as I could (ha, ha, that's a joke!) and wound it about 4 times as long as what I needed. I snipped out the best section of the spring and then, with a bench grinder and a tuna can of water , squared up the ends.  I think that using an allen wrench as a mandrel helps to keep the spring wire from slipping and therefore reduces spring-back after you remove it from the mandrel. But the spring I.D. did open up to about .100-.110, just what I needed, but the O.D. was too big to fit in the hole. So I slipped the spring onto a barely-loose-fit piece of stiff wire and went back to the bench grinder. I held the spring against the side face of the grinding wheel and let it spin moderately on the wire mandrel, using my finger to control the speed. Plenty of dips into the water and it ended up with a wire cross section somewhere between round and "D" shaped. It is now about .010 in dia smaller than the hole, to allow for dia growth during compression. Using an online spring calculator the spring has a rate of about 300 pounds per inch and a coil-bind force of about 60 pounds. You can't readily buy anything like that . I'll be using it at a force of 10 to 15 pounds or so.

Springs are fairly easy to make, but it is difficult to make one that looks like it was made in a factory, ha, ha. There are all kinds of gizmos that you can make or buy to do a better job, but not usually worth it.
Lloyd


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## Willyb (Mar 21, 2019)

Lloyd-ss said:


> I finished making all of the parts for the injector, and next will be the final assembly of it, and then testing it for functionality.
> I hope it works, LOL.
> 
> Here's how its "supposed" to operate.
> ...



Good day  Lloyd-ss
I would't install a pressure gauge in your injection system unless you are absolutely sure it is full of fuel and has zero air in it. Most pressure gauges are made with a curved tube with one end connected to the pressure source and the other plugged. This makes it very hard to get the air out of the dead ended tube. If you have any air in your injection system, it's not going to work. The miniscule amounts of fuel being injected in these small diesels can easily be offset by a bubble of air in the injection system. When injection takes place the air compresses instead of the fuel being injected. 
Keep up the good work.

Cheers Willy.


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## Lloyd-ss (Mar 21, 2019)

Thanks Willy. Yes, I was thinking about the purging process. The gauges would only be used during some prelim testing, and it might or might not work, but I'll give it a try. I was planning on doing the testing with a water soluble coolant/lube,  mixed fairly rich. Should be safer that way but I don't know how close the performance would be to diesel fuel. We'll just see how it goes.
Lloyd


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## weir-smith (Mar 22, 2019)

Lloyd

Just noted your diesel build and its good to see someone else giving it a go as there are very few around. Approximately two years ago, I commenced to build a true diesel of no particular type. It was made from material that I had on hand and to my own design based on a horizontal type engine with a 40 mm bore and a stroke of 80 mm using an auxiliary shaft to drive the fuel pump and valve cams. The valves were mounted on the side of the cylinder head e.g. top and bottom. The purpose of the build was to see if I could make it work using diesel as the fuel. I have learn much during the build - mostly what not to do however, I have learnt a lot about diesel engines.

Initially, all the components were made and the first test to start the engine was a complete failure. The problem was where to start to work out what was wrong. The first thing was the compression, as the design required 500 psi or better if it was to work. I removed the head and replaced it with a temporary head with an inlet valve and the exhaust valve which had a pressure gauge fitted. The valves were inline types that were good for 2000 psi. After cranking the engine, the best I could do was just over 200 psi. The piston was remade to allow for four more rings and retested and I now had better than 500 psi. Next was to test the valves and both failed at approx. 300 psi, so more grinding and heavier springs. I now had the basis of an engine that should work however, no such luck.

I put a pressure gauge on the fuel pump and the best I could do was about 600 psi. Eight more attempts were made to build a pump and the best I could do was just over 1200 psi. Putting that to one side as I was fed up with it, I tested the injector using an injector tester. The results were not very good or consistent so I tried several designs and they all failed in some way. A friend gave me a pintal injector nozzle and out of desperation I used this as the basis of a new injector. The results were very good in that at 2000 psi it produced a atomised cloud of fuel. At lower pressures, it produced a very fine cone spray however it had a tendency to drip. Probably why it was replaced in the first instance. A new one was ordered but it is not quite the same and I will need to modify the injector body.

I still had the problem of the fuel pump. I was given a CAV pump which I dismantled to see how it was made and while doing so, someone else advised that  there were cheap small injector pumps available on Ebay. So for $25 one was ordered and while is was well out of scale, I could see how I could machine parts down to bring it closer to what I needed. However, before doing so I wanted to test it as is. On the bench, it easily produced 3500 psi which was the limit of my pressure gauge. The pump was fitted however at the required pressure 2000 psi, the auxiliary shaft was deflecting so a new mounting bracket for the injector pump cam was made. I was now in the position to give it a try and on the first test I had large clouds of white smoke which indicated unburnt fuel. The problem was in the timing so I made a disk with degrees marked and fitted it to the aux. shaft which rotates at half speed. The cams were reset and this was followed by another test and at last the engine fired but would not sustain continuous running. My temporary fuel control was very hit and miss so to speak, so that is the next thing to do to allow better control.

This account has rambled on some what however, it does show that with persistence you can achieve an outcome. I have included a photo of the pinal nozzle and I am happy to answer any question you have. The best advice I can give is to suggest that you test the critical parts at the time to ensure that they can produce what you are expecting. I also agree that you can't put a pressure gauge in the line between the pump and the injector because of the air problem. The amount of fuel is very small and it rises quickly to the "pop" pressure and then immediately drops to almost zero until the next cycle. Air in the system no mater how small will prevent the system from working. Also, I have used copper tube for the delivery to the injector and to date it has not failed however, I have purchased some 3mm stainless capillary tube to use.

My current build is a vertical air blast injection engine which has its own unique set of problems and a further engine at the startup stage is a Fairbanks Morse 3 cylinder R80 engine.

Bruce







Note, the coin is approximately 16 mm


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## Lloyd-ss (Mar 22, 2019)

Hi Bruce, I want to tell you how much I really appreciate your taking the time to detail the trials and tribulations that you went thru on your engine. And how about an award for persistence? But honestly, this is exactly the type of help I was hoping to find on HMEM. The areas that vexed you will probably vex me too, so the caution flags are up.

Your advice about testing each critical component as it is built is well taken.  That's why I built and tested the flywheel first, LOL. When mounted on a shaft with bearings, it maintains its momentum. That is at least one item in the win column. 

The pintel and seat in your photo is a commercially available part, correct? If I get stuck, the source info on that would be helpful. I have already had to re-design the internals of the injector. The items in the earlier photo functioned fine, but did not seal very well. A couple of cc's of 1000 psi air would bleed thru in about one minute, all the way down to zero. The new design is with a pintel that opens inward, like the one you have, responding to a pressure imbalance. It is interesting that I thought it was a long shot that the first design would seal properly, but I built it anyway. Lesson learned. 

The second injector should be finished today and ready for prelim testing. I do indeed expect better results with this one.
Lloyd


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## weir-smith (Mar 23, 2019)

Lloyd

Just a quick note. I think you would be better off using diesel fuel to test your injector. You will need to make an injector test pump with a pressure gauge e.g. 2000 psi or better and include a non return valve to allow the pressure to be built up. I made a test pump from an old 3T hydraulic jack. Just needed to do some cutting with the band saw followed by some welding. A bit rough however it worked and went back to the bin when I was finished. You may be able to put your hand to the real deal as there are plenty of injector test units about as they have passed their use by date with electronic injection control. 
I have included the info re the pineal nozzle and note, we now pay GST on our purchases hence the higher price.

Just one more thought re fuel pumps. I collect old injectors for bits and pieces and I was recently given a reasonably new one. The valve at the injector end is about 4 mm (approx) and fitted into a a bore that was of very close tolerance which is what you would expect. The material is very hard e.g. better than 4140 however, I think it could be ground down which I will try on my tool and cutter grinder. I need a high pressure low volume fuel pump for my current project. Using such materials makes life much easier as to machine and grind to these exact tolerances is very difficult at best.

Bruce











e.


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## Lloyd-ss (Mar 23, 2019)

Bruce,
Thanks for the additional information. I might be able to obtain that Kubota injector locally.

I ended up changing the internals of my prototype injector so that the injector pintle opens inward in a more conventional manner as the pressure goes high enough to pop the injector open. But it still leaks at the pintle tip seal so that requires some attention.





Here is the assembled injector.  The injector is also the high pressure pump.
The plan is still for the injector to be fed by a constant low pressure pump at about 50 to 100 psi, driven by an eccentric on the shaft that drives the cam shaft.  There will be  a check ball inside the inlet adapter. Opposite to the inlet fitting is a screw for bleeding and test hook-ups. The small pin that sticks out of the top of the injector is actually the top of the pump piston, and will be driven by a rocker. The end of the piston that is inside of the injector is .062" in dia, so very small. Also, inside the injector there is very little fuel volume, maybe 0.3cc, so once the system is bled of all air, and the check ball is working properly, building high pressure and popping the injector open with each piston stroke should be possible.
For scale purposes, the input line to the injector is 1/8" O.D. stainless steel, and the thread at the tip of the injector is 1/4-28.








Just for show-and-tell, this is a hydraulic burst test fixture that I made to test high pressure air tubes. Capability is to approx 30,000 psi. The black tube on the right is 1.25 O.D. x .095 wall 2024T3. Out of the picture on the left is a Harbor Freight hydraulic hand pump that goes to 8,000 psi, and serves as the first stage of the hyd system. The 2 long steel tubes to the left of the black tube are a hyd multiplier with a large input piston on the far left, that drives a smaller piston that is in the tube on the right. Multiplication is about 4 to 1. 
When testing the black aluminum tube on the right, the first failure occurred at 9,000 psi when the tube swelled and an o-ring popped. I fixed that so that the o-ring held pressure again, and then the retaining screws for a valve plug in the end of the tube plowed their way thru the aluminum tube. The failure was quick and definitive, but the tube never did really "burst". I did test some 7/8 x .065 A513 Ty5 ERW DOM steel tube and it did actually burst at 16,000 psi, which was several percentage points above the predicted failure. The test was reassuring.
Lloyd


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## weir-smith (Mar 23, 2019)

Lloyd

Firstly, an interesting setup for pressure testing. I must admit that I haven't seen something like that before. As for your injector, again I haven't come across a combined injector and pressure pump. However, it doesn't matter what the configuration of pump and injector you have, it all comes down to the volume of fuel (about the equivalent of a single drop of water or less) and it needs to be atomised or very close to it. I would suggest that you need to build a jig or similar to mount the injector/pump with an appropriate lever to operate the piston plunger. You can then see what happens or not. The problem with making small high pressure pumps is fitting the piston to the cylinder with (in reason), zero clearance. While you can't compress a liquid, because the volume in this case is so small, it fills the smallest of clearances and as a result you can't achieve the required pressure. I don't know how they achieve this commercially but they do and they work very well and hence I collect old injectors for the parts. As I said before, use diesel for the test and put some paper towel under the injector nozzle and have a critical look at the spray patten. In your setup, you will not be able to use a pressure gauge to check the pop pressure because of the air in the gauge so it will be down to looking at the spray patten.

I will be interested to see how it goes and also, your machining looks good.

Bruce


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## Lloyd-ss (Mar 24, 2019)

Hi Bruce, 
"Haven't seen anything like that before," ha, ha, I know what that means. I actually have a video of that pressure test, and some others on youtube if you search on Airgun Lab. 
I have to admit that the injector is quite a challenge. One step forward and 2 steps back. 
I finally got the injector pintle to hold pressure and, testing with air, have been able to control the pressure where it pops from 500 to about 1000 psi by varying the preload on the closing spring. I will probably have to make a new spring and preload washers to get it pop at higher pressure for better atomization  like you mentioned earlier.

And I am indeed making a test fixture with lever to test the injector. But I was drilling out the inside of the side-inlet adapter fitting on the injector to fit a check ball and all seemed good, but when I went to tighten it for testing, the ferrule is now too little for the hole and won't seal. I'll have to figure that out in the morning when I am fresh. Problem solving skills go downhill when I stay up too late, LOL.


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## Lloyd-ss (Mar 25, 2019)

Bruce, I am glad you were so candid about the number of iterations it took to get a pump and injector you were happy with. That makes me feel better. I am now on to version number 3.


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## weir-smith (Mar 26, 2019)

Lloyd 

You are joining the club building this engine and there will be a few more versions to go so patience is required. The problem will be in creating enough pressure to atomise the fuel. We are talking about very small amounts of fuel which come into to the compressible range.  If your problem is leakage past the high pressure piston then I could give you some suggestions. The other thing is, you don't appear to have a non return valve on the high pressure side. I think this could be a problem in that you are asking the the pump to go from zero to 2000 psi in one stroke with very little volume. How do you plan on adjusting the engine speed e.g. control the fuel? Your design is quite unique and I hope you are successful and you will learn much along the journey.

With my engine, I can inject from approx. 6mm to zero mm and I can adjust the stops for the range that I need. I do not concern myself with how much the pump is producing but rather measure the volume from the injector nozzle. 

Also, I checked out your videos - interesting and clearly, you know a thing or two about pressure testing. 

Bruce


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## Lloyd-ss (Mar 26, 2019)

Hi Bruce, I appreciate your sticking with me and offering your voice of experience. And believe me, I do appreciate the advice. But I also often have to prove things to myself, and who knows, I might eventually end up right where you are pointing me. When I was actually being paid for being a manufacturing engineer, creative, cost effective solutions were my forte, and managers would often ask good naturedly in Monday meetings what solutions I had cooked up in my shop over the weekend. I loved the challenge, but of course the stakes were higher there, LOL.
But the challenge of this creative hobby is what makes it so special, isn't it? Enough rambling, ha, ha.

I did indeed install a spring loaded check ball on the input to the injector. I also managed to get the air out of the system and fill it for the first time with water and emulsified oil coolant. I didn't want to use diesel until I was close to happy. Didn't want the extra mess yet. I was also able to pressurize the system up to 1500 psi and bleed it and find the leaks, and also get it to inject. Kinda disappointing. The discharge was more like someone using the toilet than a nice mist from a perfume bottle. 

This injector is supposed to (in my mind anyway) take an inlet pressure of maybe less than 1000 psi and boost its internal pressure with a cam driven piston, to a point high enough to make the injector pop open. I was not planning on a direct ecumenical connection from the cam to the injector pintle.  But I know this is old territory for many people and I also am keenly aware that there are very few "new" solutions to these problems. Most of the new solutions are ones that somebody else already developed and that I am just not aware of. 

I have to follow along the general theme that I have in mind for the injector, and when I have exhausted that, then I will take a different approach, and who knows, probably end up where you did, LOL.
Lloyd


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## weir-smith (Mar 27, 2019)

Lloyd

You are right in that you are approaching the problem from a different perspective and you need to go where it takes you. The thing to remember is, that you learn so much usually what not to do. If we all did what everyone has done, then nothing new would be developed. I would like to follow your progress and see how it works out.

For your system, you could replace the rocker bearing with an eccentric bearing that you could rotate and thus vary the gap for operation and therefore the amount of fuel injected. However, note that this will also vary the injection timing. Unfortunately everything has a tradeoff.

I have been working on the new injector housing and have come to the most difficult task in that I need to drill a no 75 hole 25 mm or one inch deep. I usually break two or more drills using a high speed drill at about 15,000 rpm. It doesn't seem to matter how careful I am and using plenty of lubricant. It is not the drill breakage but the time to recover the broken drill if it is possible. This hole carries the fuel from the inlet connection down to the pintal and needs to be very precise.

Let us know how you get on.

Bruce


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## Lloyd-ss (Aug 25, 2021)

Seeing its been 2 and a half years since I last posted, I re-introduced myself in the Introductions forum. Hopefully things are stable enough (with me) that I won't disappear again. I just re-read the first post about forgetting the 2 stroke idea and going with a 4 stroke. But, without having read that post I re-started in the 2-stroke direction. Diesels on you tube and everywhere you look. Too much temptation. And I needed ANOTHER project to start.
Here's where it is now. more info coming. Someday I will get a DRO, sigh.
Lloyd


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## Lloyd-ss (Aug 25, 2021)

Starting a Roots Blower

Trying for a 2 stroke diesel might not be a wise choice, but I'll see how it goes. It seems difficult to find dimensional data that is useful for design purposes, too. Looking at the tried and true Detroit Diesel 2-strokes with Roots blowers, each rotor appears to be approximately one and a half times the diameter of the cylinder bore. The scavenging boost, per the manual, can be up to 4psi.  The length of the rotors is a bit hard to determine as each series of DD engines has a different length. The plan for the engine is 33mm bore and 66mm stroke and the 2 Roots rotors that I made are 43.7mm dia x 27.8mm long.  I won't know how much air they will displace until I get the gears (29 tooth 1.0 mod) next week and build a housing.

Once I laid out the rotors in autocad and verified that they would roll without gaps opening up, or binding occurring, making the rotors was much easier than I was expecting. The cylindrical blanks started out as plain cylinders with a .375 +.001/-.000 hole thru the middle. Then, 6 more 3/8" holes on the mill (3 each on 2 different B.C.s).  Manual mill without a DRO, yuck. Making a solid fixture plate with full diameter 3/8" cap screws seemed to be the trick to keeping everything accurate.  The final size of the 3 valleys in the rotors was controlled by plunging them to size with a 5/8" endmill. The contoured tips of the rotor lobes are .303" radius and this was done by manually pivoting each lobe about its center with a lever/handle bolted to the top of the rotor. I turned the rpm up high, so that the 1/2" diameter contouring endmill would cut cleanly and not grab the part. Plenty of oil. Tedious, but the result is good.

Each rotor has about .002" taper per side so I just swapped ends on one of them so that the tapers offset each other. I put a pair of 3/8" pins (shanks from broken endmills) into the fixture plate to see how  the rotors would mesh and turn. I machined the center distance about .002" larger than the gears are supposed to be and the rotors turn with only slight resistance in a few places. I will probably try lapping them together with autobody rubbing compound  after I get the drive gears so that the center distance can be set correctly.

Here are some pictures of the process.

Rotor bolted to fixt plate, 7 holes drilled, plunging the lobe valleys to final size with a 5/8" endmill.







Handle bolted on to manually pivot the rotor about the lobe axis to achieve a .303" radius. The lobe must swing thru
 a 195 degree arc to be properly contoured.






Rotor machined to size and ready for final finishing.







I know that I am avoiding the whole injector situation, ha ha.
Lloyd


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## Peter Twissell (Aug 26, 2021)

Hi Lloyd,
Nicely made parts!
Looking at the way the rotors mesh together, you may need to alter the profiles to make them work when they are geared together.
In the picture of both rotors mounted on pins, it appears that the rotor on the right would need to rotate a lot more than the one on the left in that part of the rotation.
When you meshed them in autocad, did you do so by rotating both through the same angle?
From your cad model, you should be able to derive the areas of  displacement between the rotors and calculate the theoretical flow rate.
I like your manual mill setups - I do a lot of that kind of rotary table work myself.

Pete.


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## Lloyd-ss (Aug 26, 2021)

Hi Pete, Thanks for the comments. I see what you are saying about how the rotors mesh, but I spent quite a bit of time rotating them at a 1 to 1 ratio in autocad. The rotors won't drive each other. There are 3 points in the rotation where they will loose mesh, but because they are driven by mating gears to keep them in sync at a 1 to 1 ratio, they will still maintain a line to line fit thru their full rotation so that the air doesn't leak back thru the rotors. If you tried to drive just one gear instead of both of them, they would definitely lock up at 3 places in each rotation.

I think the leak-back between the rotors is called slippage which is not exactly the correct term  for what is happening. I am really anxious to get this housed and spinning to see how much air it outputs. If I drive it with a toothed belt, the overdrive ratio could be changed to possibly make up for the "slippage". Because there is clearance on all surfaces of the rotors, some amount of slippage is normal.

I am not trying to make a model of any particular engine, there is a fair amount of poetic license in my "interpretation", LOL. I change it as I go and just keep the as-built drawings up to date.
Lloyd


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## Lloyd-ss (Aug 28, 2021)

Here is some more work completed on the Roots blower rotors and housing. This is just to check the fit, and next will be work on the gear train, machining the air inlet and outlet ports, and then actual testing of the blower function. 
There is a temporary Lexan cover on the front to allow observation of the gears during operation. Two idler gears will be needed to get the rotors to rotate into each other (one CW, and one CCW) for proper airflow and meshing. Using 2 idlers will also make it easier to sync the rotors together. The final version probably will not have idlers. Lots more to do.






Lloyd


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## ajoeiam (Aug 29, 2021)

George Punter said:


> Lloyd I was interested to read this thread and see your photographs of the progress on your Diesel engine. About six years ago I followed the same path and for the same reasons. I had drawings for the 6/1 Lister Diesel engine and used these to make a scale model.  The engine is 20cc and uses direct infection into a pre combustion chamber. I used a modified gass jet as the injection nozzle and the injection pump had a bore of 4mm and a stroke of 1mm. A manual bypass was used to pass the excess fuel. The injector fuel line had check valves to prevent fuel coming back down the line. I am very much a " a try it and see if it works" type of model engineer and don't get bogged down with too much theory, but there was some discussion relating to it not being a "real" diesel. In my book if there was no spark plug to ignite the mixture so it was a Diesel engine. I have included some photographs of this engine and should you want to see it working it is on U tube  - just type in model lister Diesel engine. Good luck with your project and I will continue to follow your progress.
> George.


Hmmmmmmm - - - - very curious - - - - your source for the drawings please?


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## ajoeiam (Aug 29, 2021)

weir-smith said:


> Lloyd
> 
> Just noted your diesel build and its good to see someone else giving it a go as there are very few around. Approximately two years ago, I commenced to build a true diesel of no particular type. It was made from material that I had on hand and to my own design based on a horizontal type engine with a 40 mm bore and a stroke of 80 mm using an auxiliary shaft to drive the fuel pump and valve cams. The valves were mounted on the side of the cylinder head e.g. top and bottom. The purpose of the build was to see if I could make it work using diesel as the fuel. I have learn much during the build - mostly what not to do however, I have learnt a lot about diesel engines.
> 
> ...



Reading back (to before my join date) - - - - muchly appreciating your notes!!


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## ajoeiam (Aug 29, 2021)

Lloyd-ss said:


> Hello everyone.
> ...............................................
> This thread actually started a few days ago on the general engine discussion forum, but it seemed like it really belonged on this forum, so here it is.
> How to fit mismatched rings and piston and cyl bore??
> ...




You don't mention it explicitly but - - - - am I understanding correctly - - - your inner flywheel ring was made from the same 8" pipe with a slot cut into it so that you could fit this inner ring into the outer ring (uncut 8" pipe)?

I've thought of making a flywheel from say a chunk of 1" or 1-1/2" thick steel cut into shape using a cutting torch. 
Likely could also be made stacking some bits of 3/4" thick steel cut in similar fashion.


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## ajoeiam (Aug 29, 2021)

Lloyd-ss said:


> Bruce,
> 
> snip
> 
> ...



Hmmmm - - - I downloaded the pic and enlarged it using software but I can't read the gauges. 
Would like to get more details on this setup as it would seem something that would be very very useful. 
(the ratings on the pressure gauges is I think mainly what I'm looking for but if you have more notes (so far you seem to have such) they would also be 
useful - - - - I'm trying to force myself to take more notes here to ease future stuff development - - - -memory is pretty good but all too often after 5 or especially 10 or more years there are details missing!!! - - - notes is what helps the memory - - - grin!! (thanks for the impetus!!!))
Dunno about board recommendations but maybe to make this info more easily 'find-able' a new thread may be quite useful - - up to you though!!


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## ajoeiam (Aug 29, 2021)

delete (please - - - for one of the admins)


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## ajoeiam (Aug 29, 2021)

Lloyd-ss said:


> Here is some more work completed on the Roots blower rotors and housing. This is just to check the fit, and next will be work on the gear train, machining the air inlet and outlet ports, and then actual testing of the blower function.
> There is a temporary Lexan cover on the front to allow observation of the gears during operation. Two idler gears will be needed to get the rotors to rotate into each other (one CW, and one CCW) for proper airflow and meshing. Using 2 idlers will also make it easier to sync the rotors together. The final version probably will not have idlers. Lots more to do.
> snip
> Lloyd



When you are checking your 'blower' besides checking for volume and pressure would you be able to check for vacuum producible?

AIUI a blower can function as a vacuum as well.


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## djswain1 (Aug 29, 2021)

Lloyd-ss said:


> Hi Bruce, I appreciate your sticking with me and offering your voice of experience. And believe me, I do appreciate the advice. But I also often have to prove things to myself, and who knows, I might eventually end up right where you are pointing me. When I was actually being paid for being a manufacturing engineer, creative, cost effective solutions were my forte, and managers would often ask good naturedly in Monday meetings what solutions I had cooked up in my shop over the weekend. I loved the challenge, but of course the stakes were higher there, LOL.
> But the challenge of this creative hobby is what makes it so special, isn't it? Enough rambling, ha, ha.
> 
> I did indeed install a spring loaded check ball on the input to the injector. I also managed to get the air out of the system and fill it for the first time with water and emulsified oil coolant. I didn't want to use diesel until I was close to happy. Didn't want the extra mess yet. I was also able to pressurize the system up to 1500 psi and bleed it and find the leaks, and also get it to inject. Kinda disappointing. The discharge was more like someone using the toilet than a nice mist from a perfume bottle.
> ...


An injector with integrated pump is called a "unit injector" in case you don't know. Interesting build will be following along


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## Lloyd-ss (Aug 29, 2021)

djswain1 said:


> An injector with integrated pump is called a "unit injector" in case you don't know. Interesting build will be following along


Yup, I am learning the diesel jargon. It seems like the 2 most common mechanical types that are applicable to the diesel model engines are the (1) unit injector :located in the head, driven by a cam and  rocker arm, with the pump and injector as a single unit, and bypass for excess fuel back to the tank. Correct? (2) Separate, matched pump unit and injector unit, with the pump driven off the cam shaft, and only the injector mounted in the head. I think that is right.

At the earlier urging of  Bruce (I think), I purchased the smallest and cheapest pump and injector pair that I could find, to take apart and see what makes it tick. It seems like the injector and pump are the major bug-a-boo for model diesels.  And seeing this is my first build, I have no qualms about, if it is absolutely necessary, machining excess material off the purchased items to install on the model. I know it is a cop out, but I am not copying any particular design and am a pragmatist, not a purist.   Hopefully I won't have to do that, LOL.

Here is a pic of the "type 186" parts I bought, which probably put out 10 times the volume I need. You can see the volume control lever on the pump. I imagine it is more precision, than complicated. Each item is about 3" long.


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## Lloyd-ss (Aug 29, 2021)

ajoeiam said:


> When you are checking your 'blower' besides checking for volume and pressure would you be able to check for vacuum producible?
> 
> AIUI a blower can function as a vacuum as well.


Sure, testing for vacuum will be easy once I get it operating.
It has been mentioned before about how "scaling" kind of falls apart as the models get smaller and smaller. I think the roots blower will have that problem, too. On the full size units, there is a few thousandths of an inch clearance between all mating surfaces. On the model version, the clearances will probably be about the same because that is about as accurately as I can make the parts. So, the clearances, and therefore the leakage, are a far bigger percentage on the model unit compared to the real unit. Something will need to compensate. More overdrive?
Lloyd


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## Lloyd-ss (Aug 29, 2021)

Peter Twissell said:


> Hi Lloyd,
> Nicely made parts!
> Looking at the way the rotors mesh together, you may need to alter the profiles to make them work when they are geared together.
> In the picture of both rotors mounted on pins, it appears that the rotor on the right would need to rotate a lot more than the one on the left in that part of the rotation.
> ...


Hi Pete, I took your advice and calculated the area of each "empty" lobe space. It looks like each lobe space is approx 0.36 cuin, and that each rotation should transfer thru 3 lobe spaces for a displacement of 1.08 cuin per revolution or 17.7 cc/rev.  Given that the proposed swept cylinder volume is 56 cc, that means at least 3.2 revs of the blower to fill the cylinder if the blower is 100% efficient. If the efficiency is really only 50%, then the overdrive might need to be 6.4 to one????? Hmmm. I need to double check that. Thoughts? The detroit diesel blowers only run at about 1.5 overdrive, but there are so many variables. Maybe the displacement is equal to 6 lobe spaces  per rev, rather than 3?
Lloyd


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## djswain1 (Aug 29, 2021)

Lloyd-ss said:


> Yup, I am learning the diesel jargon. It seems like the 2 most common mechanical types that are applicable to the diesel model engines are the (1) unit injector :located in the head, driven by a cam and  rocker arm, with the pump and injector as a single unit, and bypass for excess fuel back to the tank. Correct? (2) Separate, matched pump unit and injector unit, with the pump driven off the cam shaft, and only the injector mounted in the head. I think that is right.
> 
> At the earlier urging of  Bruce (I think), I purchased the smallest and cheapest pump and injector pair that I could find, to take apart and see what makes it tick. It seems like the injector and pump are the major bug-a-boo for model diesels.  And seeing this is my first build, I have no qualms about, if it is absolutely necessary, machining excess material off the purchased items to install on the model. I know it is a cop out, but I am not copying any particular design and am a pragmatist, not a purist.   Hopefully I won't have to do that, LOL.
> 
> ...





Lloyd-ss said:


> Yup, I am learning the diesel jargon. It seems like the 2 most common mechanical types that are applicable to the diesel model engines are the (1) unit injector :located in the head, driven by a cam and  rocker arm, with the pump and injector as a single unit, and bypass for excess fuel back to the tank. Correct? (2) Separate, matched pump unit and injector unit, with the pump driven off the cam shaft, and only the injector mounted in the head. I think that is right.
> 
> At the earlier urging of  Bruce (I think), I purchased the smallest and cheapest pump and injector pair that I could find, to take apart and see what makes it tick. It seems like the injector and pump are the major bug-a-boo for model diesels.  And seeing this is my first build, I have no qualms about, if it is absolutely necessary, machining excess material off the purchased items to install on the model. I know it is a cop out, but I am not copying any particular design and am a pragmatist, not a purist.   Hopefully I won't have to do that, LOL.
> 
> ...


Yes essentially, but there are lots of different injection systems and variations. Plunger pumps can be driven from the main valve camshaft or their own seperate camshaft. Small engines especially single cylinder usually have a separate plunger (or jerk) type pump injection like the parts you have purchased. The type 186 are copies of the Yanmar L series which is one of the most common "modern" single cinder air cooled industrial engines. It is a direct injection (DI) engine with a multi-hole type injector nozzle. The pintle type nozzle is probably the easiest design to use they are usually on indirect injection engines (IDI). You should be able to download an L series service manual which may have details if the pump & injection.
IDI engine usually have flat top pistons and a pre-combustion or swirl chamber into which the injector injects. DI engines have shaped bowls in the piston crown with the injector, injectng directly nto the cylinder. Glow plugs can be used on DI & IDI.
Regards, Dave


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## Peter Twissell (Aug 29, 2021)

Lloyd, the displacement of the blower is 6 lobe spaces per revolution.
Thus, at 3.2 to 1, the blower displacement is equal to the cylinder displacement, giving similar volumetric efficiency to a conventional crankcase induction 2 stroke.
Pete.


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## Lloyd-ss (Aug 29, 2021)

Peter Twissell said:


> Lloyd, the displacement of the blower is 6 lobe spaces per revolution.
> Thus, at 3.2 to 1, the blower displacement is equal to the cylinder displacement, giving similar volumetric efficiency to a conventional crankcase induction 2 stroke.
> Pete.



Pete, great, 6 lobe spaces per rev is more pleasing for the overdrive! Thx


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## Lloyd-ss (Aug 29, 2021)

ajoeiam said:


> Hmmmm - - - I downloaded the pic and enlarged it using software but I can't read the gauges.
> Would like to get more details on this setup as it would seem something that would be very very useful.
> (the ratings on the pressure gauges is I think mainly what I'm looking for but if you have more notes (so far you seem to have such) they would also be
> useful - - - - I'm trying to force myself to take more notes here to ease future stuff development - - - -memory is pretty good but all too often after 5 or especially 10 or more years there are details missing!!! - - - notes is what helps the memory - - - grin!! (thanks for the impetus!!!))
> Dunno about board recommendations but maybe to make this info more easily 'find-able' a new thread may be quite useful - - up to you though!!


Joe, I am going to combine a few responses into one and hopefully won't miss anything.

Flywheel-
Yes, for the inner band on the main wheel, I did the math and cut a section of the inner band and then squeezed with some bar clamps and forced it into the main outer wheel. It jammed in plenty tight. I am sure there are as many different ways to make a flywheel as there are hobbyists. For me it boils down to: what material do I have on hand, or what can I easily buy, what tools do I have, and what skills do I have, or think would be useful to learn. For me, the limits were poor welding skills, and a lathe that was barely big enough.

Lister drawings- I don't have clue about those.

Note taking-
wow, we all have our own methods, and it is a real pain when you forget what you did or how you did it.  Spreadsheets, drawings, often partial drawings, but decent as-built drawings even if only I can understand them. A project notebook and a project folder on the computer. Plenty of pictures, with useful names, and the so-so pictures either deleted or put in an archive folder. Then maybe a few videos. I built high performance air rifles for a number of years and did a lot of material testing (airgun lab on you tube), so record keeping was pretty important so that if someone needed something fixed 5 years down the road, I had some info.

Pressure test fixture.
Here is a slightly better picture. The low pressure side gauge is a 10,000 psi gauge from McMaster. Maybe $15 or $20. The nice 30,000 psi high pressure gauge (30,000 psi full scale, 15,000 at 12 o'clock) is a deal I got on eBay. New it is ridiculous. PM me if you need other info about the test setup, but first check out my airgun lab youtube videos. I have lots of material test videos including tube burst failure tests, screw shear strength tests, and more.


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## Lloyd-ss (Aug 31, 2021)

First Test of the Roots Blower. 

The real setup will have a 29 tooth gear on each rotor shaft, meshed directly to each other. And, real bearings. This setup is made from gears salvaged from the planetary gearset from a battery powered drill. Even if there was only .001" backlash for each gear, plus, adding a little runout here and there, the needed .002" clearance between all the surfaces of the rotors, is totally hosed up. The rotors could be rotated manually, demonstrating proper clearances, but driving via the geartrain, there was clicking and clacking all the time.

Prior to testing, I operated the rotors within the housing and end plates with lapping compound and oil to remove any high spots. That process worked well and I took everything apart (again and again and again) to clean it all up and try rotating it, checking for clearance and smoothness. When I thought it was good, I attached the Rube Goldburg geartrain, and what a disappointment. If either rotor lobe is .001" too early or too late, they click. At .003" it makes a clack.  At .005" everything locks up. Hopefully the larger 29 tooth gears will eliminate that problem.

I did test for pressure and only got a half psi from the outlet. I could feel suction on the inlet. I think, in the end, the blower itself will work properly. But this geartrain is garbage.

Lessons learned (actually, relearned for the umpteenth time):
Don't get greedy. You can see a 1/8" aluminum plug in the cover near a screw. I was using a 4-40 tap in the housing, and was at the point where I knew the tap needed to be backed out and cleaned and more oil added. But I only needed 1/8 more turn. You know what happened. There was 2 hours of crappy rework.
Be patient. I had my doubts about the improvised geartrain. The proper gears are still a week away. Should have waited.

Some habits are almost impossible to break.
Lloyd


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## Lloyd-ss (Sep 2, 2021)

djswain1 said:


> Yes essentially, but there are lots of different injection systems and variations. Plunger pumps can be driven from the main valve camshaft or their own seperate camshaft. Small engines especially single cylinder usually have a separate plunger (or jerk) type pump injection like the parts you have purchased. The type 186 are copies of the Yanmar L series which is one of the most common "modern" single cinder air cooled industrial engines. It is a direct injection (DI) engine with a multi-hole type injector nozzle. The pintle type nozzle is probably the easiest design to use they are usually on indirect injection engines (IDI). You should be able to download an L series service manual which may have details if the pump & injection.
> IDI engine usually have flat top pistons and a pre-combustion or swirl chamber into which the injector injects. DI engines have shaped bowls in the piston crown with the injector, injectng directly nto the cylinder. Glow plugs can be used on DI & IDI.
> Regards, Dave



Dave, 
thanks for all the injection info. You know your diesel systems! I took your advice and downloaded a copy of the Yanmar service manual for the single cylinder L series diesels. I bought the 186 pump and injector 2-1/2 years ago and they seem applicable, design-wise. But golly, they are big and heavy, about 4" long. Made for years of service and abuse, I guess. The manual shows how to disassemble and what makes them tick. Trying to "skinny them down" looks like it would be a futile effort. A good learning tool, though.
Lloyd


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## Lloyd-ss (Sep 3, 2021)

*The Roots Blower is working *

I had doubts at times, but the Roots blower is now working reasonably well. It has advanced from Proof of Concept, to Prototype.
The actual pressure and flow still need to be measured, but calibrated thumb pressure, LOL, shows significant output pressure and input suction at 2500 rpm. Flow appears to drop off with rpm but below 750 rpm, the flow is very anemic. The Detroit Diesel maintenance spec calls for about 4 psi at 2000 rpm and I think this blower is definitely there.

I ended up making a pair of 36 tooth gears, one being the drive, and the other the driven. The mill setup was kind of cheesy with a few hand-ground tooth profile cutters that approximated an involute. The spin fixture had an easy 36 spaces, so that is where the tooth choice came from. My 9 year old grand daughter was hanging around and wanted to "drill something" so she turned the table crank back and forth between the stops as I indexed the spin fixture. She was VERY proud of her work   as she also did the final light sanding on the tooth tips and scrubbing them with soap and a brush in the sink.

There was a tedious amount of hand fitting and sanding and polishing of the rotors to get them to rotate with only a tolerable amount of noise. There is still quite a bit of work to do on the blower, mainly, real bearings.
A question comes to mind. With such little scavenging airflow from the blower at low RPM, will auxiliary air be needed during start-up? Possibly mini air tank and air motor for starting?
Lloyd

*Drive and driven gears showing Inlet port*






*Outlet port*
The black lube you see here and there is a little bit of moly. In the end, rotors will need to run w/o lube.




To do the testing, I am setting the blower gear-side-down on the drill press in a vise and driving it with a 5/32 hex bit in the left-side socket head "drive" screw.

Video and pressure test coming the next few days.


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## djswain1 (Sep 3, 2021)

Lloyd-ss said:


> Dave,
> thanks for all the injection info. You know your diesel systems! I took your advice and downloaded a copy of the Yanmar service manual for the single cylinder L series diesels. I bought the 186 pump and injector 2-1/2 years ago and they seem applicable, design-wise. But golly, they are big and heavy, about 4" long. Made for years of service and abuse, I guess. The manual shows how to disassemble and what makes them tick. Trying to "skinny them down" looks like it would be a futile effort. A good learning tool, though.
> Lloyd


No problem. Yes I think it is the difficulty of minuaturising the fuel injection system that is the main reason few diesel models are built. At least with a model there are not any strict performance or emissions criteria to adhere to. Often the main criteria (ignoring aesthetics) are that it starts and runs...
I can see by your approach to the blower you aren't one to throw in the towel at the first hurdle ;-)
Cheers, Dave


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## Vietti (Sep 3, 2021)

Any chance some of the noise is gear noise?  Really neat project!

John


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## Lloyd-ss (Sep 3, 2021)

djswain1 said:


> No problem. Yes I think it is the difficulty of minuaturising the fuel injection system that is the main reason few diesel models are built. At least with a model there are not any strict performance or emissions criteria to adhere to. Often the main criteria (ignoring aesthetics) are that it starts and runs...
> I can see by your approach to the blower you aren't one to throw in the towel at the first hurdle ;-)
> Cheers, Dave



Thanks Dave. You are correct, I have no delusions that this will be at all easy. It might be impossible for me. Who knows? 
Looking at the level of perfection and skill and knowledge of the members on this forum, I am totally humbled and in awe. I am seeing that there are tips/tricks/techniques that will help, and in the end, if I get it to actually fire... by whatever means, I will be thrilled. And I will be 100% honest  if I have to use "unapproved" techniques to get there the first time.
Lloyd


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## Lloyd-ss (Sep 3, 2021)

Vietti said:


> Any chance some of the noise is gear noise?  Really neat project!
> 
> John


Hi John. I was thinking about that when I first got it rotating, too. I worked on smoothing the gears up some and then spun them in the housing with the shafts and end plates installed but the rotors removed. Eventually I got them to be almost silent. (my hearing isn't that great, ha ha) But after putting the rotors on the shafts, I could feel the interference points as I rotated the assembly with a hex bit and slow speed drill. I would take the rotors out and work on the problem areas, and put it back together (with index marks) and try again. Eventually, they ran kinda smoothly, but the noise was definitely coming from the rotors clicking together here and there. I don't want to remove any more material until I get some proper bearings in place  and get the runout under control. Each effort results in an incremental improvement. It DOES test one's patience, and I am sure I hear some chuckling from members, LOL. Trial by fire.
Lloyd


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## Ghosty (Sep 3, 2021)

Lloyd-ss, Invest in a set of gear cutters, then you can cut the gears to mesh with almost no backlash, and would be able to get it to spin over very easy.
Cheers
Andrew


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## Lloyd-ss (Sep 3, 2021)

Andrew, yup, I know you are right. I can buy gears relatively inexpensively, but being able to dial in the center distance and backlash when necessary would be very nice. I worked at a gear shop in Detroit in the '80's and know how beautiful nicely made gears can be. And the Roots blower needs zero backlash, for sure.
Thanks for planting that bug in my ear about a few cutters. I've just never needed the capability before; but maybe now.
Lloyd


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## Ghosty (Sep 3, 2021)

Lloyd, I have bought 3 sets at the moment(Mod 1, 0.5, and 0.4) still looking at getting a 1.5 and mod 2 sets, also looking at DP24 and was looking at the DP64, but the Mod 0.4 is exact copy. I'm working on a step up counter rotating gear box for RC boat at the moment.
Cheers
Andrew


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## Lloyd-ss (Sep 3, 2021)

Ghosty said:


> Lloyd, I have bought 3 sets at the moment(Mod 1, 0.5, and 0.4) still looking at getting a 1.5 and mod 2 sets, also looking at DP24 and was looking at the DP64, but the Mod 0.4 is exact copy. I'm working on a step up counter rotating gear box for RC boat at the moment.
> Cheers
> Andrew


Andrew,
thanks for sharing those pictures of your gear train work. Can I call them inspirational? I had planned on the inevitable need to re-make few of the parts for the roots blower. Surprisingly, I think the rotors themselves are ok. The housing and end-plates are ok, too.  But new shafts, gears, and bearings are necessary if this thing is going to work. The end plates are thick enough that they can be counterbored for the shaft bearings. 
It looks like you are using fully sealed ball bearings at both ends of each shaft, is that correct? 
Progress is slow, but the learning process is really amped up.
Lloyd


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## Ghosty (Sep 3, 2021)

Lloyd,
They are fully sealed but they still leak, Oil leaks out, not very quickly, but it does leak, may be to do with pressure, or speed, input is almost 19,000rpm, but when there is only 3ml of oil to start with you have to keep on top of it.
The gear box shown is the one I am replacing, it has a ratio of 1-1.07 , new one is 1-1.15.
And the boat that it goes in.
It is all trial and some error when designing from scratch, just have to keep at it, took three goes to get the gear box design right.
Cheers
Andrew


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## Lloyd-ss (Sep 3, 2021)

Ghosty said:


> Lloyd,
> They are fully sealed but they still leak, Oil leaks out, not very quickly, but it does leak, may be to do with pressure, or speed, input is almost 19,000rpm, but when there is only 3ml of oil to start with you have to keep on top of it.
> The gear box shown is the one I am replacing, it has a ratio of 1-1.07 , new one is 1-1.15.
> And the boat that it goes in.
> ...


That yellow thing looks like it is going 100mph while still on the bench! 19,000 on those fast pitch props sounds crazy. 
I like the collet/flarenut arrangement for quick disconnect from the props. A serious hobby.
Thanks! Lloyd


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## ajoeiam (Sep 4, 2021)

Lloyd-ss said:


> snip
> And the Roots blower needs zero backlash, for sure.
> snip



Hmmmmmm - - - - I would have thought that of all places a machining type forum would NOT promulgate the idea that ZERO error could ever be achieved. 

(It is possible to get backlash very low - - - - but its NEVER zero!!!!)


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## Lloyd-ss (Sep 4, 2021)

ajoeiam said:


> Hmmmmmm - - - - I would have thought that of all places a machining type forum would NOT promulgate the idea that ZERO error could ever be achieved.
> 
> (It is possible to get backlash very low - - - - but its NEVER zero!!!!)


OK Joe, let me start by saying that I do have a smile on my face   right now although the text of this message might not sound that way. My last 25 years of work were as a manufacturing engineer, where setting people up for success was the goal, and esoteric discussions were neither understood nor appreciated. But I also worked with the hardcore design theorists/research engineers where a joke about someone not knowing that the cosecant and cotangent of extremely small angles are "essentially" identical, would bring a hearty round of laughter. They understood the esoteric discussions, when time permitted.
I used the qualifier "essentially" and I guess I could have said that the backlash should be "essentially"  zero, but I didn't. Didn't think it was necessary given the context of the conversation.
But I will give you 2 examples where the backlash can be zero. If you roll a newly ground steel gear against a master gear to inspect center distance variation and find that the max is 10 millionths of an inch, I would say that that test fixture operates at zero backlash. The other is when I was making the aluminum gears to try on the blower in this thread. As I was creeping up on the proper tooth thickness/backlash, I installed the gears on the assy and got it where I could barely rotate by hand. I could feel the bump-bump from tooth to tooth as the clearances were all used up and the soft aluminum of the teeth yielded enough to rotate while maintaining point to point (line to line) contact.

Whether we call it zero backlash, or almost zero backlash, doesn't matter to me. I want it to feel, with my fingertips, like there is no backlash, and, if you checked with a dial test indicator, (one .0001" per graduation), you probably couldn't say for sure if there was or was not any backlash.  I am still smiling! 

Different subject. Just wondering, did the additional picture of the high pressure hyd test fixt show you what you were curious about?
Enjoy your weekend!
Lloyd


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## Lloyd-ss (Sep 7, 2021)

Roots Blower Pressure and Volume Tests - Video and pictures

The Roots Blower is working well enough for testing, but not well enough to used in a working model engine. Proper bearings and gears are required, but the rest of it should be serviceable. After much reading about positive displacement blowers, like the Roots, I became quite curious about the actual performance. It seems like using the Roots as a supercharger, to get several pounds of boost was not part of the original design goal, but it certainly has been adapted well, using better sealing and very high overdrive speeds.

The old Detroit Diesel Roots blowers ran at 1 to 1 to about 1.3 to 1. Pressures were up to 4 psi at 2,000 rpm, but I am not sure how that was measured. The blower that I made is about a 1/5 th scale version of a DD 1-71 blower. But even though the blower is 1/5 th scale, the clearances between the rotors themselves, and the housing are still at a 1 to 1 scale, so the leakage (slippage) in the blower might be proportionally 5 times greater in my model than in a real DD Roots. And, that shows up during the testing. 

I set the Roots up on an old drill press and am driving by a hex bit via a piece of rubber hose to serve as a flex joint.  For the test setup, the output goes into a PVC plenum that is 67cc in volume. There is a pressure tap off the side of the plenum that is hooked to a manometer that reads in inches of water column. The pressures are very low and I didn't have a gauge that would read that low, accurately. The end of the 67cc plenum has a 3/8" hole (9.5mm) drilled in the end of it. When the blower is in operation for testing, the air can be monitored 3 ways. First, it can just exhaust out the 3/8" hole and the back pressure in the plenum is recorded. This pressure is very low. The next reading is with the 3/8" hole bushed down to .182" (4.6mm). This increases the back pressure some more. Using the back pressure readings, and the exit orifice size the approximate volume of that that is being pumped can be calculated. 





						Calculator: Air Flow Rate through an Orifice | TLV - A Steam Specialist Company (North America)
					

Online calculator to quickly determine Air Flow Rate through an Orifice. Includes 53 different calculations. Equations displayed for easy reference.




					www.tlv.com
				




Lastly, tif the exit port is plugged, the manometer will give the maximum pressure that the Roots will make at that particular rpm. I guess pump curves could be graphed from all the various readings.

Vacuum. Because the Roots is symmetrical inside, by driving the rotors from the hex head screw on the other rotor, the rotors turned backwards and the pressure plenum became a vacuum plenum when the orifice was plugged. I was pleasantly surprised to find that the max vacuum was almost the same as the max pressure at same rpm.

Here is the test set-up.



Here is the internal dimensions for the Roots



Here is the outlet port, which is the same as the inlet port. Are they big enough?



Here is the video of some of the actual testing.
I will tabulate the actual test results in the next post.
Lloyd





Your browser is not able to display this video.


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## Lloyd-ss (Sep 7, 2021)

Pressure and Volume Test Results from Roots Blower.

The Roots Blower that I made has a pair of 3-lobed rotors 44mm in dia and 27.8 mm thick. The p.d. and the  C to C distance is 29mm. The inlet and outlet ports ar 20mm x 16mm. Each lobe has 3 "empty spaces" of about 5.9cc. Each revolution pumps 6 empty spaces from the inlet port to the outlet port, so the pump through-put at 100% efficiency could be 35.4 cc/rev . As a side note, because the Roots is symmetrical inside, if the direction of rotation of the rotors is reversed, the in and out directions are swapped.




Because the 2-stroke diesel that I have in mind is about 56.4, even if the Roots operated at 100% eff, the rotors would need to run at 1.6 to 1 (60% overdrive) to keep up with the piston movement. 100% eff, no way!

Here are the test results fro the various rotor speeds:

*1,040 rpm*
Maximum developed pressure (with outlet blocked)(in inches of water column):
     7.12" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
  .182" hole:
   2.37" W.C.
  19,820 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
  .375" hole:
  0.22" W.C.
  25,770 cc/min
Theoretical swept volume of the Roots blower at 1040 rpm (at 35.4 cc/ blower rev):
   36,820 cc/min,  max theoretical

*1,510 rpm*
Maximum developed pressure (with outlet blocked)(in inches of water column):
     12.75" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
  .182" hole:
   4.63" W.C.
  27,690 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
  .375" hole:
  .62" W.C.
  42,760 cc/min
Theoretical swept volume of the Roots blower at 1,510 rpm (at 35.4 cc/ blower rev):
  53,454 cc/min,  max theoretical

*2,150 rpm*
Maximum developed pressure (with outlet blocked)(in inches of water column):
     21.75" W.C.
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
  .182" hole:
  8.25" W.C.
  37,090 cc/min
Blower chamber pressure measured, and volume calculated, with air exiting the plenum through a
  .375" hole:
  1.25" W.C.
  60,880 cc/min
Theoretical swept volume of the Roots blower at 2,150 rpm (at 35.4 cc/ blower rev):
  76,110 cc/min,  max theoretical


*How does the scaling to Detroit Diesel 1-71 look?*
As I stated previously, this little Roots blower is approximately 1/5 th linear scale to 1-71 Roots.
The swept volume of the DD roots blower, per rev, is equal to about one cylinder's worth of air per engine rev. In other words, 71 cuin of air per rev, or 1,163 cc of scavenge air per revolution, or 1,163,000 cc of air per minute at 1,000 engine rpm. (Note- edit made to this paragraph to correct math errors)

The blower I am working on is supposed to be 33mm bore x 66mm stroke, for 56.4cc/rev. Doing the simple math:
56.4 x 500  rpm  = 28,200 cc/min (for 1 cyl fill of air per rev)
56.4 x 1,000 rpm = 56,040 cc/min (for 1 cyl fill of air per rev)
56.4 x 1,500 rpm = 84,600 cc/min (for 1 cyl fill of air per rev)
56.4 x  2,000 rpm = 112,800 cc/min (for 1 cyl fill of air per rev)

Looking at the performance per rev chart, above, it looks like approx 1,510 rotor rpm might be a good starting point for 1,000 rpm engine speed, which would require at least a 1.5 to 1 overdrive for the 2 rotors.
There might be some mistakes in my math or logic, so please let me know if you spot anything.

Lloyd


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## Richard Hed (Sep 8, 2021)

Lloyd-ss said:


> Pressure and Volume Test Results from Roots Blower.
> 
> The Roots Blower that I made has a pair of 3-lobed rotors 44mm in dia and 27.8 mm thick. The p.d. and the  C to C distance is 29mm. The inlet and outlet ports ar 20mm x 16mm. Each lobe has 3 "empty spaces" of about 5.9cc. Each revolution pumps 6 empty spaces from the inlet port to the outlet port, so the pump through-put at 100% efficiency could be 35.4 cc/rev . As a side note, because the Roots is symmetrical inside, if the direction of rotation of the rotors is reversed, the in and out directions are swapped.
> View attachment 128952
> ...


Do you have the plans for this? I was working on a two lobed roots blower but got nowhere as I didn't have a quality enough mill--that is I didn't have ANY mill.


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## Peter Twissell (Sep 8, 2021)

Nice work Lloyd!
Good to see that your test results correlate well with calculated flowrates at higher rpm. This is to be expected, as the leakage in the blower is constant through the rpm range.


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## Lloyd-ss (Sep 8, 2021)

Richard Hed said:


> Do you have the plans for this? I was working on a two lobed roots blower but got nowhere as I didn't have a quality enough mill--that is I didn't have ANY mill.



Richard, yes I do have some drawings of the rotors and housing. They are just 2d autocadd drawings, but the mesh of the rotors seems to be good throughout 360 degrees of rotation. The rotors are not true cycloids, but close approximations of them. All features on the rotors are portions of a circle, as shown in the post about the actual machining of the rotors. Start by getting the gears first, so that you know what the exact center distance  between the rotors needs to be. The size of the rotors and housing are fully scalable, so you could make whatever size you want. I will post the drawings in a few days after I get them prettied up with adequate dimensions. I think I can post both pdf's and dxf's or dwg's of the blower parts.

Just like standard involute gears, where the tooth faces roll against each other with no rubbing, the cycloid shape is supposed to do the same thing, all rolling without any rubbing.
Lloyd


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## Lloyd-ss (Sep 8, 2021)

Peter Twissell said:


> Nice work Lloyd!
> Good to see that your test results correlate well with calculated flowrates at higher rpm. This is to be expected, as the leakage in the blower is constant through the rpm range.


Thank you Pete!  After reading your reply, I went back and did a few edits in post #61 to correct some fuzzy, late night, math and descriptions. I also added a "theoretical maximum" airflow at each test rpm speed, based on swept volume of the Roots rotors of 35.4 cc/revolution.  That helps shed some light on the leakage in the blower as you  pointed out.

I am a data junkie and love making  spreadsheets and graphs to display the data in various ways. You never know what sort of unexpected trend might pop out at you, or how consistent and preditable the results might be. I might collect more data at the 2 remaining speeds on the little drill press, 585 and 3,000 rpm. There might be the makings of some actual pump curves, or at least my interpretation of a pump curve. The science of this adds a whole 'nother dimension of enjoyment of this hobby for me. But the cool thing is, you only need to get into the science as much as you want to, or even not at all. Great fun!

Also, I want to give a big thank you to ALL of the members of the forum who display and share their projects and ideas and comments. The challenges undertaken, and successfully completed, are true inspirations for a new novice member. 

Lloyd


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## Richard Hed (Sep 9, 2021)

Lloyd-ss said:


> Richard, yes I do have some drawings of the rotors and housing. They are just 2d autocadd drawings, but the mesh of the rotors seems to be good throughout 360 degrees of rotation. The rotors are not true cycloids, but close approximations of them. All features on the rotors are portions of a circle, as shown in the post about the actual machining of the rotors. Start by getting the gears first, so that you know what the exact center distance  between the rotors needs to be. The size of the rotors and housing are fully scalable, so you could make whatever size you want. I will post the drawings in a few days after I get them prettied up with adequate dimensions. I think I can post both pdf's and dxf's or dwg's of the blower parts.
> 
> Just like standard involute gears, where the tooth faces roll against each other with no rubbing, the cycloid shape is supposed to do the same thing, all rolling without any rubbing.
> Lloyd


When I was working on this, nearly 30 years ago, an engineer friend told me .012 clearance was good, but I thimpfk that is too much.  I woujld thimpfk that a thou would be fine if one could achieve it.  Is there any reason, other that making sure there is no actual contact, for making such huge clearances?


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## Lloyd-ss (Sep 9, 2021)

Richard Hed said:


> When I was working on this, nearly 30 years ago, an engineer friend told me .012 clearance was good, but I thimpfk that is too much.  I woujld thimpfk that a thou would be fine if one could achieve it.  Is there any reason, other that making sure there is no actual contact, for making such huge clearances?



Richard, Here are 2 pages from the DD 71 series manual and it does indeed call for a .012" clearance between the rotor tips and the housing.  But it only calls for a .002" clearance between the interference points between the rotors. During operation, all of the air flow is along the outside wall of the housing (air does not pass in a straight line thru the rotors. It calls for inspection every 100k miles, so i guess they figure that is where the clearances are needed. The rotors are huge and maybe they get hotter and expand more than the housing. Funny that only 2 of the clearances have max tolerances specified.

My rotors started out too tight to easily roll all the way around. Sandpaper, files, and lapping compound finally got it to rotate with some contact, but no binding. The cycloid features (like an involute gear shape) should roll past each other, not slide past each other. 

The cross section picture really shows how huge the blower is.
Lloyd


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## Steamchick (Oct 5, 2021)

Lloyd-ss said:


> OK Joe, let me start by saying that I do have a smile on my face
> I used the qualifier "essentially" and I guess I could have said that the backlash should be "essentially"  zero, but I didn't. Didn't think it was necessary given the context of the conversation.
> But I will give you 2 examples where the backlash can be zero. If you roll a newly ground steel gear against a master gear to inspect center distance variation and find that the max is 10 millionths of an inch, I would say that that test fixture operates at zero backlash. The other is when I was making the aluminum gears to try on the blower in this thread. As I was creeping up on the proper tooth thickness/backlash, I installed the gears on the assy and got it where I could barely rotate by hand. I could feel the bump-bump from tooth to tooth as the clearances were all used up and the soft aluminum of the teeth yielded enough to rotate while maintaining point to point (line to line) contact.
> Whether we call it zero backlash, or almost zero backlash, doesn't matter to me. I want it to feel, with my fingertips, like there is no backlash, and, if you checked with a dial test indicator, (one .0001" per graduation), you probably couldn't say for sure if there was or was not any backlash.  I am still smiling!
> ...


Just an observation from a real amateur - when it comes to gears, thrust faces, contact points, sliding surfaces, etc.... but  Doctor Engineer in Tribology once told me that you always want sufficient clearance for the "molecules" of oil to roll between the peaks of the metal crystalline structure. This is what he called zero clearance, I.E. where the oil lubricated at "minimum film", without being "sheared" and rapidly broken down. He was talking of a minimum of 40 microns (4 x 10E-5) clearance in main and big end plain bearings in car engines. (Actually hugely greater than true oil molecule sizes. ~10 E-10m. A C60 molecule is about 0.7nm, =7 x 10E-10.!). He also advised that "minimum clearance" is naturally broken within gears, which is why oils for gear boxes have to have special oils (additives), to resist this mechanical breakdown. I think the additives are large molecule  mineral compounds, dissolved in the oils, but never got to work on gear oils so have no real knowledge.
Not knowing, I wonder if running the gears so tight is actually going to run-in the gears, or simply distort and damage the ball races? Or will a very soft and fine abrasive (toothpaste?, Brass polish?) assist in running-in the high spots of the gears? I am not sure what you are trying to achieve by running gears "tight"? Are you simply marking high spots to be dressed with a tool or stone slip? Or are you trying to work harden the surfaces, or wear them away metal to metal?
I do think buying proprietary tooling to make the gears will be one step more accurate than grinding your own tools. So you have done the right thing there IMHO.
Enjoy, and keep posting on this interesting subject.
K2
K2


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## Lloyd-ss (Oct 6, 2021)

Steamchick said:


> Not knowing, I wonder if running the gears so tight is actually going to run-in the gears, or simply distort and damage the ball races? Or will a very soft and fine abrasive (toothpaste?, Brass polish?) assist in running-in the high spots of the gears? I am not sure what you are trying to achieve by running gears "tight"? Are you simply marking high spots to be dressed with a tool or stone slip? Or are you trying to work harden the surfaces, or wear them away metal to metal?



Steam, Thanks for your detailed response and questions. I might have been a bit snarky in response #59 to Joe, and if it came across that way, I apologize. That certainly was my intent.

Steam, your questions got me to thinking, and my general thought processes. Most of previous small size machining has been lathe work for PCP air rifles working in the 3,500 psi range.  A lot of precision lathe work, but basically no mill work that precison center distances.  Now, this roots blower is basically 2 sets of gears, involute and cycloid, turning on the same shafts and requiring rotor clearances of a few thousandths of an inch inside the blower housing. Basically, my shop equipment isn't capable of achieving without some tricks. Again, I am still learning at a basic level, in blissful ignorance, determined to make it work.  The reason I want "minimal" backlash between the 2 involute gears is because all accuracies throughout the blower must be held to a high degree so that the cycloid gears of the blower will rotate smoothly without interference.  

If you look at the tolerance stackup, a .001" change in center distance will cause about a .0014 change in backlash. This backlash affects the clocking of the cycloid gears. Add in a .001" circular runout in a couple of places and there could possibly be another .003" backlash. Now, one bad thing about cycloid gears is that with a pair 3 tooth gears, one cannot drive the other because they will lock up every 1/3 rotation. So, as the backlashes and tooth thicknesses, and runouts, all accumulate, they all end up being transfered to the cycloid gears. Then, add on top of that, that each time the scavenging ports are opened by the piston travel, the Drive, and the Driven loading on the 2 cycloid gears might reverse. If the accumulated backlash is too great the cycloid gears could jam. 

The blower in the pictures is really more of a proof-of-concept device than anything else, although it DOES work, but just not well. I now have on hand some purchased steel mod1 gears (which match the design C to C distance), some flanged bronze bushings, some sealed ball bearings, and some 3/8" 1144 stress proof rod for the shafts. Basically, I will be keeping the rotors, endplates, and housing, and adding new gears, shafts, and bearings.

I can see why some of you guys make your own gears so that you can control the tooth thickness and therefore, the backlash. so much to learn, but that is what it is all about!
Lloyd


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## Steamchick (Oct 6, 2021)

Lloyd. Don't apologise. Your explanation sounds good. This is a very "technical" build, much more than the "average machinist" may attempt - knowingly. In my experience, there are many superb machinists, but only a fraction of them can discuss the engineering and explain "what's what" as you do. 
I look at it that "Toolmakers" and "Engineers" are the angels of different religions. Each may think they (and their "reilgion")  are the most important, but each needs the other to get the best from their combined abilities.
Thanks,
I am enjoying the technicalities of the thread. (Though I know my desires and limitations, and will never be making a roots blower! Even though I know my bike would be a much better performer with one.).
K2


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## Lloyd-ss (Oct 6, 2021)

I did run a pump volume test (the Roots Blower)  using the set up shown in the video in post #60. Basically, I attached a sealed and flattened  33 gallon plastic trashbag to the pump to see how fast it would fill the bag, and how much pressure it would max out at when a "leak" hole was cut into it.  At 2.150 blower rpm, it filled the 33 gallon bag (125,000 cc) in about 100 seconds.  The leak hole was to simulate the scavenging ports, kinda. After some number crunching it looks like the blower might barely keep up with an engine running at 1,200 rpm with the pump being drive at 40% overdrive. A crude test, but at least it shows the blower is working.
Lloyd


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## Lloyd-ss (Oct 6, 2021)

Steamchick said:


> I look at it that "Toolmakers" and "Engineers" are the angels of different religions. Each may think they (and their "reilgion") are the most important, but each needs the other to get the best from their combined abilities.


Very well said.  I could use a good toolmaker angel.....please.
Lloyd


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## Lloyd-ss (Mar 15, 2022)

ROOTS BLOWER - THE ON-GOING SAGA

It has been a few months since I was last here, so first I want to say thank you to the true, hardcore members of the forum who are on here almost every day. You folks are the real life-blood, and I appreciate that. I feel a little cheesy just dropping in and out occasionally, but I do think about this a lot and work on it whenever I can.






To make a long story short, this was darn difficult, and very humbling. A CNC probably would have helped, but the clearances as the rotors rotate is soooo critical, that just a tiny discrepancy allows leakage from the positive pressure side to the negative, and the airflow basically stops.

The 2-lobe was the worst. Even though it has a huge swept volume, if the rotors don't stay in mesh 100% of the time, the flow drops to zero. The 3-lobe was only marginally better.

Then I started giving it some more serious thought, from the perspective of not having a cnc. The more lobes the rotor has, the closer the profiles can be approximated with circular arcs, so that they are always in contact. The 2 lobe is the worst, with only a short section of circular arc at the root and the tip. So all the rest of the cheesy cycloid approximation is just wide open leakage paths.

The final (maybe, LOL) 6 lobe is made from PTFE, which has good temperature qualities and can be run with almost zero clearance. I also used flanged ball bearing this time that can be preloaded with the lock nuts. I only ran it for a minute at 1500 RPM,  but the thumb-test revealed some decent positive pressure.






Even though the swept volume of the 6 lobe is only one half that of the 2 lobe, a single point of failure does not make it loose ALL of its pressure. It will still pump some air, rather than NO air at all.






Next will be to set it up for testing to see how much flow and pressure it can achieve, and try and figure what what "adequate flow", might be.

Thanks to everyone who has shared their failures on the forum and showed that if you want it to work, you just keep trying. It made me realize that I am not the only one.
Lloyd


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## ajoeiam (Mar 16, 2022)

Lloyd-ss said:


> ROOTS BLOWER - THE ON-GOING SAGA
> 
> It has been a few months since I was last here, so first I want to say thank you to the true, hardcore members of the forum who are on here almost every day. You folks are the real life-blood, and I appreciate that. I feel a little cheesy just dropping in and out occasionally, but I do think about this a lot and work on it whenever I can.
> 
> ...




Nice work. 

A wondering - - - - these blowers are NOT a new thing - - - - wondering how they were fabricated 'back in the day' say the 1950s. 
Anyone out there have any ideas?


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## Lloyd-ss (Mar 16, 2022)

ajoeiam said:


> A wondering - - - - these blowers are NOT a new thing - - - - wondering how they were fabricated 'back in the day' say the 1950s.
> Anyone out there have any ideas?


Great question! I have not researched, and do not know. But I am always amazed at the ingenuity and artistry of machinists from the past. Someone here must  know.

There is a question that has been driving me a little crazy that I am sure a lot of the more experienced model builders have the answer to.  It has to do with scaling of the models and how it changes the functioning of the actual model.

My roots blower is maybe one fifth scale.  Each rotor is 1.62" long and 1.66" in diameter. If this were a 2 lobe rotor, each "space" would have  a volume of approx 1.92 cubic inches. And for arguments sake say that each lobe space has linear seal/leakage lines of 3 lengthwise and 2 on the ends. That would be approx 8.1 linear inches.

The full scale rotor (5 times as big) would have a volume of 5 cubed x 1.92 cubic inches (EDIT, 5 cubed, not 5 squared) =5x5x1.92=48 cubic inches. =5x5x5x1.92= 240 cubic inches NEW ANSWER  But its linear gaps would only be  5 times bigger, 5x8.1=40.5 linear inches. Correct??

So for the full sized 2-lobe blower  you have  EDIT  .84 .17 NEW ANSWER linear inches of leakage path per cubic inch, and for the one fifth scale you have 4.2 linear inches of leakage path per cubic inch.

So to me, it looks like the one fifth scale model has EDIT  5 times NEW ANSWER  24.7 times the leakage potential of  the full size. Of course, the scale model should have closer tolerances and therefore the leakage potential will be less than that.  I am quite confused as to what the practical real-world implications of the scaling are. I am also wondering if this is beyond my skill level? I do want to get it to work, though.  Thanks for any thoughts.

EDIT-Frankly, I am shocked that my math shows 24.7 times as much leakage potential for the one fifth scale model. (Probably should be 25 due to rounding errors).  Is that correct ??? Thanks! Lloyd


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## Steamchick (Mar 17, 2022)

Cam-following milling machines were used long before CNC was developed. The Cam being a shaped lump of metal, not Computer-Aided-Machining. WW2 did a lot to improve machining development in the USA, Germany, Japan and UK.
Even in the 1980s~1990s I saw machine shops making pistons (and lots of other things) using machines that "followed shaped cams" - e.g. for piston skirts that were NOT circular. But these were being superceded by machines that followed a "computer" shape with servo driven tooling.
K2


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## Steamchick (Mar 17, 2022)

Hi Lloyd,
That sounds like you do some good calculations. Anything (like gases and leaks) that have a combination of square and cube factors cannot scale directly. linearly. e.g. model aircraft have a thicker wing than real full sized aircraft - simply to make them work. All about ratios like Reynolds numbers, etc... that are a simplification of the squares, cubes, etc. of nature.
I do a bit of work on steam boilers. Nothing is scale, except perhaps the external size and shape. Even then there are usually compromises. e.g. Water in water gauges doesn't follow scale due to the meniscus following the "water" characteristic, due to surface tension, of climbing up the glass. Below a certain size of tube, the surface tension dominates pressure differences of the water level. And steam bubbles can block the whole device anyway, when the bubble diameter is large enough to touch the tube all around, when surface tension over-rules the pressure differences that would otherwise cause the bubble to float through the liquid water.
Anyone who has attempted to make a small single cylinder ICE engine will know all about leakage when their compression is very low! - Just as you are learning. It is a part of the reason we had to develop better materials and machining to make smaller and smaller ICE engines than the early huge cylindered engines. Same applies to hydraulics, as well as pneumatics.
Cheers!
And good luck! - I am sure you'll succeed with some perseverance.
K2


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## Lloyd-ss (Mar 17, 2022)

Steamchick said:


> Cam-following milling machines were used long before CNC was developed...........


Steam, ahhh, that is the direction I was thinking. Thank you so much for your experience and input about when there were a lot of dedicated machine set-ups and the tool crib was filled with lots of big hulking specialty fixtures. A lot of ingenuity.  
I was around for the middle of the manual-machine-to-cnc evolution as a YPE (young punk engineer) and just sucking it all in being amazed at how all these beautiful metal parts were made. I was in heaven! 
There was a problem that had come up with a 10 to 1 template dresser on a pump-gear finish grinding machine. It ground the individual tooth spaces between the gear teeth. They could not get a proper profile on the large template and when the finished gears were rolled against a master gear, the ink paper trace showed an ugly bump-bump-bump as the gears rolled together. I had had just enough Fortran programming to think that I might be able to help. They gave me a chance and I worked with the math and geometry guru there to learn how the profiles were mathmatically generated. My first attempt was disheartening because it was not much better than what they had. But the guru was very understanding and we finally realized that my understanding of how the tooth space was measured (perpencicular instead of circular) was incorrect. I fixed that in the program (using cnc to generate the manual 10 to 1 template) and it worked. I can remember being so excited as I saw a few random out-of-charcter smiles popping up. I was on my way to loosing the YPE name tag. A wonderful time.
Lloyd


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## Lloyd-ss (Mar 17, 2022)

Steamchick said:


> .........Nothing is scale, except perhaps the external size and shape. Even then there are usually compromises.......


Steam, you have no idea how much anxiety that comment has relieved. Thank you so much.  There are so many gorgeous scale models that I always assumed were scaled all the way down to every nut and bolt. But now I see that that is not the case. The tribal knowledge and tricks take over to make it look scale, but still be able to function. As I build this thing in my head while riding around on the lawn mower, I have actually been thinking about compression ratios and how to design the head for the engine so that the compression ratio could be adjusted up or down after it doesn't work the first time. Sometimes it is all about knowing the tricks. Thank you for the insight.
Lloyd

(Sorry for the rambling posts, but sometimes I get on a roll and can't stop.)


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## ajoeiam (Mar 17, 2022)

Lloyd-ss said:


> Steam, ahhh, that is the direction I was thinking. Thank you so much for your experience and input about when there were a lot of dedicated machine set-ups and the tool crib was filled with lots of big hulking specialty fixtures. A lot of ingenuity.
> I was around for the middle of the manual-machine-to-cnc evolution as a YPE (young punk engineer) and just sucking it all in being amazed at how all these beautiful metal parts were made. I was in heaven!
> There was a problem that had come up with a 10 to 1 template dresser on a pump-gear finish grinding machine. It ground the individual tooth spaces between the gear teeth. They could not get a proper profile on the large template and when the finished gears were rolled against a master gear, the ink paper trace showed an ugly bump-bump-bump as the gears rolled together. I had had just enough Fortran programming to think that I might be able to help. They gave me a chance and I worked with the math and geometry guru there to learn how the profiles were mathmatically generated. My first attempt was disheartening because it was not much better than what they had. But the guru was very understanding and we finally realized that my understanding of how the tooth space was measured (perpencicular instead of circular) was incorrect. I fixed that in the program (using cnc to generate the manual 10 to 1 template) and it worked. I can remember being so excited as I saw a few random out-of-charcter smiles popping up. I was on my way to loosing the YPE name tag. A wonderful time.
> Lloyd


I have been digging for info. 
Have found a number of academic papers. 
Are you interested in wading through them?
(I'm not guaranteeing that they're totally useful - - - just that they 'might' be useful.
I'd do some reading myself just that I've got a lot going right now and thought you might want to start soonish and and and . . . )


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## Lloyd-ss (Mar 17, 2022)

Joe, sure, I'd love to take a look.


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## ajoeiam (Mar 18, 2022)

Lloyd-ss said:


> Joe, sure, I'd love to take a look.



Hmmmmm - - - - what is the best way to send such to you? 
Do I use a private message (not sure about official rules and don't want sanctions!!!) or do I send them directly to you?
(You could send me your email addy in a private message - - - - maybe?)


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## Lloyd-ss (Mar 18, 2022)

Joe. Conversation just started.


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## Lloyd-ss (Mar 20, 2022)

The 6 lobe roots blower seems to be working ok. The inlet opening was enlarged for improved airflow, and it appears to have worked. I had to cobble up a crude locking collar for the "driven" gear so that the gears could be precisely timed with the rotors.  The plastic gears and the teflon rotors, locked together as they are, do not play well with each other.  The 4-40 cross bolt is secured into the shaft, but the gear is slotted to allow for approx +/- one half tooth of adjustment.  Hand-fitting was tedious, but lessons-learned from the failures paid off.









I also ran a functionality test. Running at 1,510rpm, it filled a 125 liter plastic trash bag in approx 4 minutes, or 31.1 liters per minute.  31.1 liters divided by 1,510 revs = 20.6 cc/ rev. Calculations for the blower are 29.2 cc/rev (with no losses), so I guess 20.6cc/rev is reasonable for an actual output.  Unfortunately, if the diesel cylinder volume is 56cc, that would require at least a 2.7to one overdrive to purge the cylinder every revolution, which might not be practical. Forward progress is slow, but the learning is healthy.


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## Lloyd-ss (Apr 22, 2022)

*The Latest Version of the Roots Blower is WORKING !*

Finally! I have been around the world twice on this and ended up back with the original 3-lobed design, but totally revamped.  I ended up with better bearings and gears, and tighter clearances. But that still wasn't enough. The ratio of the clearances to the effective swept volume was still too much to stop the "slippage" between the rotor lobes. See post #75 for more about this. 
The last set of 3 lobed rotors are made out of Teflon so that the clearances can be kept to a minimum without galling, but they ALSO had to be made somewhat flexible such that under centrifugal force, they would expand in such a way that the mating rotors would conform to each other, and seal to each other, without binding up. This was accomplished by drilling larger thru-holes in the 3 lobes to make the walls of the lobes thinner in certain areas so that they had flexibility where needed, and rigidity where needed in other areas.

Here is a quickie video that I made of the roots blower powered by a little drill press at approx 2500 rpm. The tubing filled with blue tinted water serves as a pressure gauge. The Roots blower is a positive displacement blower that moves air, but doesn't build significant pressure (unless modified extensively). At most, the blower would build up maybe 20" of water. BUT, it pumped a lot of air.

I fastened a 125,000 cc plastic trash bag to the outlet of the blower and it filled in about 55 seconds, running at 2500 rpm. Previous versions had taken from 2 and half to over 4 minutes.

If we just say that the blower output 125,000 cc's in one minute, and divide that by the proposed 56 cc displacement, that is 2232 cylinder fills in one minute. Since this is for a 2 stroke, the blower rpm of 2500 might support an engine rpm of ..... maybe 1500?? Hard to say.

Here is the amateurish video, but I think it gets the point across. Honestly, I was a bit surprised at how well it filled the plastic bag.





Your browser is not able to display this video.


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## aka9950202 (Apr 22, 2022)

Fantastic work.  Amazing to see the bag fill and build pressure. 

Cheers, 


Andrew in Melbourne


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## Lloyd-ss (Apr 23, 2022)

aka9950202 said:


> Fantastic work.  Amazing to see the bag fill and build pressure.
> Cheers,
> Andrew in Melbourne



Andrew, thanks for the words, I appreciate that.  And Steamchick offered encouragement several posts back with "perseverance." Yes, it paid off.

Here are a couple of detail pics.  The end plates are pinned into place and each has 2 flanged, sealed, ball bearings positioned in flanged cups. Each cup is bored slightly eccentric to give some adjustability in where the center of rotation for each rotor and gear is located. Because one rotor is "driven", and one "follows", huge amounts of fiddling was required to get the clocking and alignment and clearances correct. But no matter what I tried, the air "slippage" made the output of the blower much lower than it needed to be. I was ready to go to another type of air pump, and was thinking about vane pumps and how they maintain continuous contact as they rotate.

For ref, the right hand rotor in the pic rotates CW and the left rotates CCW.

So I thought I'd take a risk (pass-fail modification) and using a utility knife, cut all the way down thru the trailing-side of each rotor lobe. My thought was that the centrifugal force would sling the weakened rotor out enough to maintain contact throughout rotation. It didn't exactly work, so I thinned the internal wall of the leading-side of each lobe to weaken them to add some flexibility. That worked. A lot of hours in this madness. 




This pic shows the PVC adapter installed onto the outlet of the blower with 2-faced tape. The small tube coming out of the outlet adapter is a pressure tap that goes to the water-column pressure sensor.


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## Lloyd-ss (Apr 23, 2022)

*Will the Blower Pump Enough Air?*

Here are some thoughts and questions about this Roots blower.
First off, we know this application works in real life in the 100's of thousands of 2-stroke Detroit Diesels that were produced. I remember here in the US, that the Greyhound buses would always go flying by on the interstate, with that familiar blown 2-stroke sound.
I know this blower pumps air. The 125,000 cc  plastic bag was stretched tight after just over a minute of pumping at 2,500 RPM.





Here is the inside of the blower and each lobe space calculates out to 11.3 cc's, and one complete revolution should pump six lobe spaces, or (at 100% efficiency) 67.8 cc. At 2500 rpm, that is 169,500 cc's. Does that mean the blower is 125,000/169.500= 74% efficient.  That is extremely hard to believe, but maybe since the pressure only builds up to 15 or so inches of water, maybe that is true.




So here is the real question(s). How many revs of the blower would be needed to purge a 56 cc cylinder?  And how about a method to test to see if it* will actually *purge 56cc while at operating speed?  This is a head-scratcher.
Lloyd


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## a41capt (Apr 23, 2022)

Lloyd-ss said:


> *The Latest Version of the Roots Blower is WORKING !*
> 
> Finally! I have been around the world twice on this and ended up back with the original 3-lobed design, but totally revamped.  I ended up with better bearings and gears, and tighter clearances. But that still wasn't enough. The ratio of the clearances to the effective swept volume was still too much to stop the "slippage" between the rotor lobes. See post #75 for more about this.
> The last set of 3 lobed rotors are made out of Teflon so that the clearances can be kept to a minimum without galling, but they ALSO had to be made somewhat flexible such that under centrifugal force, they would expand in such a way that the mating rotors would conform to each other, and seal to each other, without binding up. This was accomplished by drilling larger thru-holes in the 3 lobes to make the walls of the lobes thinner in certain areas so that they had flexibility where needed, and rigidity where needed in other areas.
> ...


Now THAT is cool!

Congratulations!!!

John W


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## ajoeiam (Apr 23, 2022)

Lloyd-ss said:


> *Will the Blower Pump Enough Air?*
> 
> Here are some thoughts and questions about this Roots blower.
> First off, we know this application works in real life in the 100's of thousands of 2-stroke Detroit Diesels that were produced. I remember here in the US, that the Greyhound buses would always go flying by on the interstate, with that familiar blown 2-stroke sound.
> ...



Good go there sir!!!!!!!!!!!

This may be time for the equivalency testing situation. 

I also have no idea of the calculations involved - - - but if you compare the volume created by a blower for a Detroit diesel of its mated size you would have at least some kind of idea of how close you are in your endeavors. 

At the very least you are one huge heap closer to getting something that works - - - your iteration does something - - - quite impressively I would add. 

How much volume are you purging - - - how much are you providing (from your blower)?
If your volume supplied (maybe per minute for each - - - dunno - - - maybe per second) is say 115% of required - - - - well - - - I'd say - - - try it!!

(Sometimes trial and error beats a lot of calculations and might even be faster - - - grin!)


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## Lloyd-ss (Apr 24, 2022)

a41capt said:


> Now THAT is cool!
> Congratulations!!!
> John W





ajoeiam said:


> Good go there sir!!!!!!!!!!!
> This may be time for the equivalency testing situation.
> .............
> (Sometimes trial and error beats a lot of calculations and might even be faster - - - grin!)



Thanks gents. The encouragement is appreciated and sometimes that is what keeps me going on this.

I crunched some numbers for the inlet (scavenge) port timing to see how long the inlet port would have to purge the cylinder.  Even with a fixed port size, there is a way to vary the port timing.

This engine might be too large for a model, but I don't know. The plan was 56cc, 33mm bore x 65.5mm stroke.
I found many examples of inlet port and exhaust valve timing in a 2 stroke diesel One in particular was given for the DD. Exh valve opens 83 deg BBDC, inlet port opens 49 deg BBDC, inlet port closes 49 deg ABDC, Exh valve closes 62 deg ABDC.  That means that the power stroke only lasts 97 deg of crank rotation, and the compression takes place in only 118 deg of crank rotation. Doing some calcs, at 1000 rpm, the exh valve is open 24.4 msec, and the inlet port is open  16.3 msec.  At 2000 rpm the inlet port is open for only 8.2 msec.

So, at 2000 rpm, the air has to flow thru the cylinder at a velocity of 4 meters per second to theoretically totally purge the cylinder. Thinking in the imperial system, that converts to 787 feet per minute, or 9 miles per hour. I don't know if my numbers are correct, but a velocity of 9 mph for air seems achievable.

One of the variables I mentioned has to do with conn rod length. The longer the conn rod, the longer the piston will dwell at the top and bottom of the stroke (do I have that backwards??) [ darn, I am pretty sure I stated that backwards. the shorter rod has more piston dwell at the top and bottom of the stroke.], and this affects the actual length of the inlet ports.  With a minimally short conrod of 68.6mm (65.5mm stroke), the inlet port if timed for 49 deg BBDC, will be 6.6 mm long. If the conn rod is made very long at 114mm, then the port length is increased by 2mm to 8.6mm long. That is 30% more area in the inlet ports.   It seems like a longer conn rod and longer inlet port will help the engine breath better. Maybe.
Lloyd


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## Steamchick (Apr 24, 2022)

Fag-packet calculation:
Engine displacement and rpm:
56cc x 2500rpm: One cylinder fill per Rev.
=> 140litres per minute: 
Your pump makes 125litres per minute... but at 1.04barG. = 130l/min.
So maybe the engine will run? but won't run really well. So can you make a blower half as long again, (or whatever?) to exceed the displacement (at atmospheric pressure) and even give you some boost?

Probably of no use whatsoever...but, as an aside, 
I think that modern motorcycle scooters a la Vespa and Lambretta, but now made by Piaggio, and lots of others (not the electric toy scooters like single wheeled skate-boards with a steering handle), have 125cc engines with small blowers to boost their inlets. I have also seen an electric blower to boost and engine...
Universal 3" Electric Turbocharger Air intake for Car/Motorcycler/Truck/ATV/RV – Grandado.com ...
Mini Turbocharger For Small Engines Motorcycle RHB31 For ALTO | eBay 
It may be possible to get enough information from these to understand what actual volume and pressure they produce, and for what size/power of engine, so you can get some better clues as to sizing your blower?

Thanks for previous compliment, but I don't really deserve any, as I have more "stupid" ideas issuing from my brain than "sensible".  
Enjoy what you are doing, as we enjoy your posts!
Thanks,
K2


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## awake (Apr 25, 2022)

Impressive - both the results and the perseverance!


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## Lloyd-ss (Apr 25, 2022)

Steamchick said:


> Fag-packet calculation:
> Engine displacement and rpm:
> 56cc x 2500rpm: One cylinder fill per Rev.
> => 140litres per minute:
> ...




Steam,
I agree that at a 1 to 1 drive ratio, that the blower will be a bit anemic for a 56cc 2 stroke.  But with a 2 to 1 overdrive, it might work ok...... as long as it doesn't blow up. I have not figured out why Detroit Diesel decided on a Roots blower back in 1935. Was that the best option? Seems like a difficult item to manufacture for just blowing air.
Real calcs and specs for diesel blowers are hard to dig up..... but I probably just haven't dug in the right place yet. I need to cobble up some kind of flow test to get some better data.  Those tiny blowers are kind of sketchy on specs. The AMR500 min roots blower claims 500cc of air per rev and they recommend it for a max engine size of 1.6 L.  My blower might produce 67 cc/ rev, but I am pretty sure that the AMR500 can be driven at major overdrive ratios. So they are easily putting out 500cc x overdive ratio per rev.

Time to go outside and work in the garden and ponder the blower situation while performing mindless tasks. That's about as good as my multitasking gets, LOL.

_P.S.  Wrote this reply yesterday and then forgot to post it. So much for multitasking, LOL._


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## mu38&Bg# (Apr 26, 2022)

AMR500 will produce 1.8 pressure ratio or ~12psi of boost. High performance engines will have peak primary pressure ratio of ~1.5 just before transfers open. There must be pressure to push the charge through the ports against cylinder pressure which takes time to drop. Slower engines give a bit more time for blowdown and transfer. Obviously, engines run at part throttle when crankcase pressures are much lower, but the effect on power is clear.

The key will be making the blower components as precise as possible.

Here's some motivation. superchargedsaitopics

https://www.rcuniverse.com/forum/glow-engines-114/1580599-roots-supercharged-saito-engine.html gets interesting at post 18.


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## Steamchick (Apr 26, 2022)

Just a curiosity: Nissan made a March/Micra with a Super-turbo" set-up - for rallying/performance. A guy in work had one and raced it with he=is local rally club. The Supercharger worked up to 3000rpm (or something?) then a magnetic clutch disengaged and the turbo took-over boosting the engine. I am not sure if the waste-gate closed automatically, (open during supercharging) or by some electronic actuator. But the guy said he could never feel the changeover as engine performance, but he could hear a slight change of turbo note - probably as it came on/off load? Not that he was interested, as he was fully focused on racing...
I'm sure the supercharger took a bit of a pounding when the clutch engaged as the engine revs dropped through the transition point?
I think that basically, the turbo and supercharger were in parallel.
Nissan Micra K10 March Super Turbo Technical Specs, Dimensions (ultimatespecs.com)
Enjoy!


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## Lloyd-ss (Apr 26, 2022)

dieselpilot said:


> AMR500 will produce 1.8 pressure ratio or ~12psi of boost. High performance engines will have peak primary pressure ratio of ~1.5 just before transfers open. There must be pressure to push the charge through the ports against cylinder pressure which takes time to drop. Slower engines give a bit more time for blowdown and transfer. Obviously, engines run at part throttle when crankcase pressures are much lower, but the effect on power is clear.
> 
> The key will be making the blower components as precise as possible.
> 
> ...



Diesel,
That was a nice read from ptechllp about his build of the supercharger for the Saito engine. I especially appreciated his candor about the entire process.
Several take-aways from that discussion. One is that it was a major learning experience. I can attest to that. Proper (tight) clearances are hard to achieve. I agree. And your statement about the need for precision is definitely true. That is one of the major reasons for the 4 different versions that I have built. And with a CNC, I don't know if I can do much better on my manual machines.

But there are some major differences for the diesel that I am "trying" to build compared to the Saito engine.
One main factor is that the air from my blower into the diesel must be clean and dry, with no lube in it. I don't want the diesel to pre-ignite or run away. To help with that I have used sealed ball bearings and Teflon rotors. The Teflon allows for the "rubs" that the rotors have with certain parts of the housing, and with each other, to happen without the parts galling together. The sealed bearings should operate without lube. The Saito supercharger has lube in the air stream passing thru it to keep it happy.

Another very important difference is the  RPM of the 2 systems. The Saito operates up to 9,000 rpm. My diesel might get up to 2,500(?) or maybe a little more. The reason that this is so important is because of the handicap it puts on the low RPM engine. The _static pressure_ output of the blower increases with the square of the increase in RPM. Triple the RPM, and the pressure output goes up by a factor of 9.  That is major.
Also, the_ flow rate_ increases proportionally with the RPM of the blower. Triple the RPM and the flow volume goes up by a factor of 3. And that RPM vs air flow volume is pretty much a "must have" for the application.

And yes, I totally agree that in order for the scavenging to work at all, the pressure from the blower has to be noticeably higher than the residual pressure in the cylinder.  Having sufficient pressure and flow is my major concern right now. I want to verify that, somehow, before i get much deeper into the project.  I am not at all sure what that residual pressure be, but I imagine it will vary with RPM, just like the blower output pressure.
Lloyd


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## Lloyd-ss (Apr 26, 2022)

Here are a few pics and a short video from testing the Roots blower with a rotating shutter to simulate one of the standard Detroit Diesel inlet port timings of : Open 49 degrees BBDC, close 49 degrees ABDC. 98 degrees total open time.  For reference, the exh valve(s) opens 83 degree BBDC and closes 62 degrees ABDC. Therefore, the exh valve opens 34 degrees before the inlet ports are exposed so that the blower isn't hit with massive backpressure from the combustion process.

The blower is being driven at 2580 RPM and the shutter is at approx 700 RPM. No particular reason for the shutter speed, but that is what that drill operates at.  The shutter window looks narrower than 98 degrees because the diameter of the hole that it is exposing has to be added to the opening of the shutter. 
Static pressures started at 3" of water at 1248 RPM, 6"at 1812 RPM, 10" at 2580 RPM, and 27" at 3600 RPM.  The pressure is supposed to go up with the square of the RPM,but there was quite a bit of leakage around the shutter that affected the pressure readings. Still, the pressure seems pretty low for the task at hand. More research is needed.

Here is the rotating plastic shutter for the tests.  The thin tubing is for pressure tap.



Here is the how the drill drives the shutter to simulate the opening and closing of the inlet (scavenging) ports.




And here it is in operation, simulating the opening and closing of the inlet port as the piston moves down and up.





Your browser is not able to display this video.


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## Lloyd-ss (May 1, 2022)

Here is a composite video about the development of the Roots Blower for the 2 stroke diesel project.  I think it will be adequate for the task, but if needed, I could improve on it down the road.
The next challenge will be seeing how difficult the fuel injection will be.


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## Lloyd-ss (May 2, 2022)

*Experimenting with Injectors now
Trying out a Yanmar Injector*

I bought a knock-off Yanmar replacement injector, 186FA, which is compatible with the 189cc to 406cc single cylinder 4 stroke air cooled engines. Even though the bulk of the injector is too large for my 56 cc engine, otherwise it might be ok. I might be able to machine some excess metal off the injector to bring the size more in proportion to the project. Or at the very least, I can learn a lot from it.

I had a pressure test fixture from a previous project and wanted to see how the injector functioned. This part  is just an injector and needs an outside pump to control the pressure and the stroke volume.  From the testing, it looks like the injector fires cleanly at 2800psi, as specified.

The firing happens near the end of the video at about 23:00.  This looks promising.

It's just a static set-up and only fires at pressure. Just for testing, nothing more. The volume isn't controlled, yet. But I do also have the matching Yanmar injector pump, which is cam driven thru the big tappet cup at the top, which controls both the pressure and the injection volume. The little ball knob on the right side of the pump rotates around to vary the injection volume.  The brains are pretty much all in the pump. The injector just delivers the dose dispensed by the pump.





Your browser is not able to display this video.





















Here is the Injector and its matching cam-driven pump. Again, both are too large for the project, but something to study.


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## Lloyd-ss (Aug 30, 2022)

*Learning Process on Diesel Injectors..... Slow*

It has been almost 6 months since my last post on this project, but I have been working on-and-off on a diesel injector.  After numerous attempts and failures I have accepted the fact that I will not be able to make 100% of the injector myself. Some of the componenets are beyond the capability of my equipment, but mainly, me.  I have been spending some time on one of the antique diesel engine forums to learn about injectors. The Pump-Line-Nozzle system, like Find Hansen makes (my hat is off to that gentleman.... more like I am in awe) for his diesels is popular. But the thought is that the 2 stroke diesel really "needs" a unit injector, which is where the pump and nozzle are consolidated into a single piece. The Detroit Diesel (GM) 2-strokes all had unit injectors.

I attempted to use the Yanmar injector nozzle, and injector pump, to make a single piece unit injector. It almost worked and would occasionally throw out a beautiful mist, but it leaked too much and basically didn't work. If it had been built perfectly/accurately, it should have worked. But it was a learning process.

Here are pictures of the original Yanmar parts, the unit injector parts, the assembled unit injector, and a drawing of it. There are some differences between the injector and my drawing. The ijector is MUCH smaller than the original parts, but still maybe too big.  The only parts that I used from the Yanmar (in this version) were the nozzle and needle. It was a fail, but wow, did I learn a lot.

I am now working with a Detroit Diesel Unit Injector (type HV6) to see what makes them tick. And I have a good diesel engine mentor in Australia who has a lot of experience and patience.
Lloyd

OEM Yanmar diesel injector and pump





The unit injector that I came up with. The Yanmar needle and tip are the only parts I didn't make.




The finished unit injector. Too bad it didn't work.


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## weir-smith (Aug 31, 2022)

Lloyd

It is interesting to hear about your journey in respect to building a true diesel using diesel as a fuel. I noted your comments regarding others who have built small diesels however, I think you will find that they are not using diesel as such but a mixture of either and light kero. Using this type of fuel requires much less compression and far less fuel pump pressure. I have made these comments previously on these pages as I have been down this journey myself. 
I am not going to go into any great detail however, I am happy to help with any question you may have.

There are some important things you have to remember. You can scale the engine but you can't scale the physics. That is, if the full size engine requires 500 psi to compression ignite the fuel, you also need to have 500 psi. I ended up using six rings to achieve this. I tried many forms of self designed pumps but the best failed at 1200 psi eg not good enough. Ended up using the same pump as you have with some modification to suit my model. My thoughts were if it worked, then I would machine it down to better suit the engine. On the bench it would achieve 3000 psi without trouble. In respect to injectors, I tried many designs  and found they all leaked one way or another. Dripping injectors don't work that well. I ended up purchasing the smallest Kubota pintal injector replacement nozzle which was about 0.5 inch dia and made a housing for it. A bit fiddly but after several attempts the result worked well. I set the pressure at about 2000 psi which gave a good atomised spray which was so fine, it was difficult to see - more like a fine mist.

Bruce W-S


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## ajoeiam (Aug 31, 2022)

weir-smith said:


> Lloyd
> 
> It is interesting to hear about your journey in respect to building a true diesel using diesel as a fuel. I noted your comments regarding others who have built small diesels however, I think you will find that they are not using diesel as such but a mixture of either and light kero. Using this type of fuel requires much less compression and far less fuel pump pressure. I have made these comments previously on these pages as I have been down this journey myself.
> I am not going to go into any great detail however, I am happy to help with any question you may have.
> ...


Very interesting
I am learning to travel using the experience of my fellow travelers  - - - I am finding there just isn't enough life to make all the trials myself. 

AIUI that atomized mist is exactly what will give the best combustion on a compression ignition engine (or diesel if you wish). 

It is reassuring to know that this can be made to work.


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## Lloyd-ss (Aug 31, 2022)

weir-smith said:


> Lloyd
> 
> It is interesting to hear about your journey in respect to building a true diesel using diesel as a fuel. ...............
> 
> Bruce W-S



Bruce, (and I see that Joe just posted about this, too),
When you call it a journey, I know that you understand. It is as much about the process as the end result. The challenge of it. I always enjoy your candor and insightful comments regarding the difficulties faced along the way. I like the expression, "It is easy to make one that works. It is difficult to make one that works well."  However, the meaning of "easy" must be adjusted for each project, LOL.
Your comments about the laws of physics are well taken and understood. I faced that with much of my airgun work. Try as I might, conventional methods yield conventional results.
And I love your project photos.

Let me ask you about bore and stroke for a model diesel. The combustion process of a diesel is limited in its flame-front speed. But Yanmar has little 3600RPM single cylinder engines with 55mm stroke 68mm bore. I think that might be pushing the limit of flame front speed and combustion duration, and therefore piston speed.

I am thinking in the neighborhood of a 50mm stroke, but slow speed, maybe 1200 or 1500rpm max. Anything faster would have increasingly foul exhaust from poorly combusted fuel. The governor would be the ultimate RPM limiter, but the physical restraints applied by the engine construction would also make slow speed the prudent choice. And the bore would be smaller than the stroke; but with the full length skirt required of a 2-stroke piston, either a very long connecting rod or a cross head are required.  

Right now, getting past the most difficult components: the blower and the injector, are the first priority. I think the engine will end up being designed around the final injector configuration, LOL. 

One final thought on the diesel fuel. Have you ever tried a cetane booster to help with ignition? I can possibly see that as "acceptable" for a true diesel. What do you think?

Lloyd


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## Lloyd-ss (Aug 31, 2022)

I found a good deal on a NOS Detroit Diesel unit injector and am learning what makes it tick.
I guess this is what good atomization looks like.






Your browser is not able to display this video.


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## minh-thanh (Aug 31, 2022)

Hi !
With a lot of testing, with some injectors on my engine
  My conclusion is - fuel atomization : Good but not so important -_* if you just need the engine running*_
   The most important thing is : The injector must be completely sealed. + The oil pump must create enough pressure to inject into the cylinder - The injection time depends on the pressure created by the pump, can inject from 45 to 22 degrees before TDC


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## weir-smith (Sep 1, 2022)

Lloyd

To answer your question, the  bore of my engine was 40mm with a 80mm stroke. The piston was 80mm long to accomodate the rings and lubrication was via drip feed. The combustion cycle was four stroke and the target RPM was 300 however, could not achieve it and it ran better at  500 to 700 RPM.
I was told by a diesel mechanic that slow revving in a model of this size is difficult as the cylinder head etc tends to cool down (not enough mass) between strokes and makes smooth running almost impossible therefore the need to up the rpm. For me, I don't know but upping the rpm certainly made it run more consistently. I also needed to increase the flywheel in size and weight to about 5kg and use valve lifters to be able to start it. I did have to resort to using a product available here in Aust. called "Start you Bastard" as used by farmers to start engines etc, to get the engine to initially to fire. 

I have moved on from this engine and have now completed a model of the Fairbanks Morse three cylinder igniter engine (1910). Also, I have all but completed an Otto Langen engine. In progress is a model of a single cylinder air blast diesel. Now there is a challenge for you. I have only come across one model that almost made it but the builder had to resort to solid injection. The big problem is keeping the compressor cool enough with inter coolers etc so it doesn't start to motor on its own. I only have access to machines one day a week these days having down sized to an apartment and having to sell my workshop equipment. I guess that is life when you are in your mid seventies. 

Bruce W-S
Western Australia


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## Lloyd-ss (Sep 1, 2022)

Bruce,
You are a busy guy! Beautiful work! I am impressed.

40mmB x 80mmS for the diesel. Wow, that's 100cc, which hardly falls into the "model" classification, LOL  .
I guess you had to use a cross head in the design?


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## Lloyd-ss (Sep 3, 2022)

*Mini HV6 Diesel Injector*

The Detroit Diesel HV6 injector served as an inspiration for my latest attempt at a mini diesel injector.

Here are the items that make up the injector.
The 7 items at the left end of the top row are actually from the HV6 injector nozzle. I had to fabricate the rest of the items.




Here is the assembled mini-HV6 injector.




Here is a side-by-side of the original and the mini. The original weighs 790 grams; the mini weighs 85 grams.




I have just started testing the mini-HV6 and it does work, although the atomization is not what I would like.  However, there are no leaks.   Some fiddling around is necessary.  Some of the problem is probably that the nozzle is capable of at least ten times the volume that the model engine will need. But, at the same time, the full size nozzle is also capable of atomizing the fuel properly at idle when almost no fuel is used.


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## ajoeiam (Sep 4, 2022)

Lloyd-ss said:


> *Mini HV6 Diesel Injector*
> 
> The Detroit Diesel HV6 injector served as an inspiration for my latest attempt at a mini diesel injector.
> 
> ...



Very nice!!

Do you think that the parts you did use from the mini-HV6 would also be 'makeable'? 
Fascinating following this thread. 

thank you all


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## Lloyd-ss (Sep 4, 2022)

ajoeiam said:


> Very nice!!
> 
> Do you think that the parts you did use from the mini-HV6 would also be 'makeable'?
> Fascinating following this thread.
> ...


Thank you Joe, I appreciate that.

If you had nice equipment, and the skill to use it, you might make all the parts except the tip with the spray holes. On that top row of parts, the only part I made was the plunger, and it is basically a .156 dia x 1.50 long hard dowel pin with some grinding done on it.  The other parts are hardened and ground, and all  the interfaces are lapped. They wring together leak-free, just like Jo blocks. In order for the pressures to build quickly and precisely enough, it seems like metal-to-metal contact is needed, with nothing that is compressible in the actual circuit. I have a few o-rings in there that are not shown, but they are really just back-up for the metal to metal interfaces. They keep any internal leakage contained.
Here is  a close-up of the Yanmar tip which is used on little engines in the 300cc range. The longish tip is .272" dia, the small tip is about .070" dia, and you can barely see one spray hole. There are actually 5 spray holes around the  tip and you need either good light and good eyes, or magnification to see them.  The Detroit Diesel HV6 tip is very similar in size except with 6 holes. How in the heck did they do that in 1945? I have a friend who worked at a textile plant in the 70's. They had similar little "spinnerets" that made the synthetic thread.  He said the spinnerets were made in a very restricted access area. I wonder why, LOL?
Lloyd


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## abby (Sep 4, 2022)

In the UK a very large textile company also made spinnerets in a restricted area , this was because they were made from platinum and liable to be stolen.
Dan.


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## ajoeiam (Sep 5, 2022)

Lloyd-ss said:


> Thank you Joe, I appreciate that.
> 
> If you had nice equipment, and the skill to use it, you might make all the parts except the tip with the spray holes. On that top row of parts, the only part I made was the plunger, and it is basically a .156 dia x 1.50 long hard dowel pin with some grinding done on it.  The other parts are hardened and ground, and all  the interfaces are lapped. They wring together leak-free, just like Jo blocks. In order for the pressures to build quickly and precisely enough, it seems like metal-to-metal contact is needed, with nothing that is compressible in the actual circuit. I have a few o-rings in there that are not shown, but they are really just back-up for the metal to metal interfaces. They keep any internal leakage contained.
> Here is  a close-up of the Yanmar tip which is used on little engines in the 300cc range. The longish tip is .272" dia, the small tip is about .070" dia, and you can barely see one spray hole. There are actually 5 spray holes around the  tip and you need either good light and good eyes, or magnification to see them.  The Detroit Diesel HV6 tip is very similar in size except with 6 holes. How in the heck did they do that in 1945? I have a friend who worked at a textile plant in the 70's. They had similar little "spinnerets" that made the synthetic thread.  He said the spinnerets were made in a very restricted access area. I wonder why, LOL?
> ...




Well - - - I do know where I can find drill bits to 0.002" dia. 

Wonder what size those holes are?
Ever tried measuring them?

TIA


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## Lloyd-ss (Sep 5, 2022)

ajoeiam said:


> Well - - - I do know where I can find drill bits to 0.002" dia.
> 
> '''''''''''''''''''''


Where? Broken off inside a part?     Ouch!

I will get another close-up pic with a piece of super-fine wire next to the holes. 
Joe, you always present these bothersome provocative questions, LOL.


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## ajoeiam (Sep 6, 2022)

Lloyd-ss said:


> Where? Broken off inside a part?     Ouch!
> 
> I will get another close-up pic with a piece of super-fine wire next to the holes.
> Joe, you always present these bothersome provocative questions, LOL.



Well - - - - I would hope not - - - then you have a 'not good' part - - - chuckling. 

Not meaning to be a royal pita but there are not too many different ways of making these very small holes. 
And - - - as diesel injectors are sorta 'common' somebody somewhere is making lots of these holes. 

I sure wouldn't want to drill a 0.002" hole using a 'sensitive' drill press. 
(Sensitive drill press is one where its you feeling the drilling and exerting the pressure to get the drilling done. 
Besides - - - that tiny little drill bit wants to turn at some seriously high rpm I would think.)


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## L98fiero (Sep 6, 2022)

ajoeiam said:


> Well - - - - I would hope not - - - then you have a 'not good' part - - - chuckling.
> 
> Not meaning to be a royal pita but there are not too many different ways of making these very small holes.
> And - - - as diesel injectors are sorta 'common' somebody somewhere is making lots of these holes.
> ...


It's quite possible though, years ago I had a job that required 0.006 holes, I used a Guhring HSCo drill with a 1mm shank and about 2 mm of 0.006 drill and 1.5mm of flutes and a 17,000 rpm Dumore 16 sensitive drill. That said, we drilled thousands of holes and I could get ~10 holes from a drill but my wife sat and drilled holes, watched tv and got ~100 holes from a drill so it is possible but a 0.002 drill is 1/3 the size. From memory, I think we ran the drill around 12k rpm in C36000 yellow brass.





						Sensitive Drill Press | Dumore Series 16
					






					www.dumoretools.com


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## ajoeiam (Sep 7, 2022)

L98fiero said:


> It's quite possible though, years ago I had a job that required 0.006 holes, I used a Guhring HSCo drill with a 1mm shank and about 2 mm of 0.006 drill and 1.5mm of flutes and a 17,000 rpm Dumore 16 sensitive drill. That said, we drilled thousands of holes and I could get ~10 holes from a drill but my wife sat and drilled holes, watched tv and got ~100 holes from a drill so it is possible but a 0.002 drill is 1/3 the size. From memory, I think we ran the drill around 12k rpm in C36000 yellow brass.
> 
> 
> 
> ...



Interesting drill press - - - thanks.


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## Lloyd-ss (Sep 7, 2022)

L98fiero said:


> It's quite possible though, years ago I had a job that required 0.006 holes, I used a Guhring HSCo drill with a 1mm shank and about 2 mm of 0.006 drill and 1.5mm of flutes and a 17,000 rpm Dumore 16 sensitive drill. That said, we drilled thousands of holes and I could get ~10 holes from a drill but my wife sat and drilled holes, watched tv and got ~100 holes from a drill so it is possible but a 0.002 drill is 1/3 the size. From memory, I think we ran the drill around 12k rpm in C36000 yellow brass.
> 
> 
> 
> ...


Interesting that your wife could get such long life out of the drills. There is quite an art to knowing how far to push tools. I know we have all run across the guy who is always beaking taps and stripping out screw heads and wringing off bolts. I call it "getting greedy," but for some folks I think they just don't have the right karma, or whatever you want to call it, and maybe never will.  For me, I always end up paying the price for getting greedy.

Regarding small drill presses, I have long wondered why there aren't horizontal or inverted drill presses to help the chips clear naturally. Or, at least I haven't seen any, nor have I tried to jury rig something like that when faced with a troublesome part. It just seems like it ought to help, but I don't really know. Probably any  easy concept that is difficult in execution.
Lloyd


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## Lloyd-ss (Sep 7, 2022)

minh-thanh said:


> Hi !
> With a lot of testing, with some injectors on my engine
> My conclusion is - fuel atomization : Good but not so important -_* if you just need the engine running*_
> The most important thing is : The injector must be completely sealed. + The oil pump must create enough pressure to inject into the cylinder - The injection time depends on the pressure created by the pump, can inject from 45 to 22 degrees before TDC


Minh-Thanh,
I am taking everything you are saying to heart. The learning curve (hill) is steep and experienced help is always appreciated
Thanks, Lloyd


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## L98fiero (Sep 7, 2022)

Lloyd-ss said:


> Interesting that your wife could get such long life out of the drills. There is quite an art to knowing how far to push tools. I know we have all run across the guy who is always beaking taps and stripping out screw heads and wringing off bolts. I call it "getting greedy," but for some folks I think they just don't have the right karma, or whatever you want to call it, and maybe never will.  For me, I always end up paying the price for getting greedy.
> Lloyd


I'm going with the idea that she had a better feel for the drill than I, her 'day job' was working in a clerical position while I was in a machine shop.


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## Lloyd-ss (Sep 9, 2022)

Diesel Injector Dilemma

After much effort and many "almost works," prototypes of a unit injector, I am about ready to admit defeat and compromise on the issue by marrying an off the shelf injector nozzle with an off the shelf injector pump. The parts will need to be modified to remove excess size and weight.

I think I will be going with the GM (Detroit Diesel) HV6 injector nozzle, and the Yanmar injector pump from their line of LA single cylinder engines (199 to 406cc).

The HV6 nozzle has much smaller holes and the internal spring can be changed to achieve different injection pressures.

Here is a pic of the 2 nozzles (GM HV6 and Yanmar LA series.) I listed some comparison specs from both stylesof injector nozzles.




What baffles me is that the Yanmar is for a much smaller cylinder volume, and operates at over 2,000psi, but has fairly large nozzle holes.
The GM operates at below 1,000 psi, has has a much larger cylinder volume, but its nozzle holes are much smaller. So much to learn, LOL.


-----------------------------

Here is a pic of the HV6 nozzle and the Yanmar injector married together.  I hope they are compatible. The design of the nozzle and the pump are fairly straight-forward (famous last words, Ha)
There is still a LOT of excess weight and material on the Yanmar pump, but I will eventually get around to putting it on a diet to make it suitable for the model I plan on making.




Testing is next. At first glance, it seems to offer resistance against the plunger from the pressure build-up, just like it should.
This is just a proof of concept prototype, unless it works, that is.  
Lloyd


x


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## ajoeiam (Sep 10, 2022)

Lloyd-ss said:


> Diesel Injector Dilemma
> 
> After much effort and many "almost works," prototypes of a unit injector, I am about ready to admit defeat and compromise on the issue by marrying an off the shelf injector nozzle with an off the shelf injector pump. The parts will need to be modified to remove excess size and weight.
> 
> ...


Very interesting!!!!!!! 

I'd say you got some good progress going!! 

Any chance you would get a measurement on the holes in the nozzles?

TIA


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## Lloyd-ss (Sep 10, 2022)

ajoeiam said:


> Very interesting!!!!!!!
> 
> I'd say you got some good progress going!!
> 
> ...


Joe,
Here is a picture of the Yanmar nozzle with a bare copper wire .006" in dia, and a silver plated copper wire of.008" dia. The .006 fit in without much trouble, but the .008 took some effort. Both wires came back out of the holes without getting stuck.If you look at the picture in post #121, you can see that the GM HV6 nozzle has holes that are significantly smaller. I did not attempt to fit a wire into those holes.
Lloyd


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## Lloyd-ss (Sep 12, 2022)

*GM nozzle and Yanmar pump. A marriage not made in heaven. Test Video.*

This video is from a few days ago after I got this proof-of-concept set-up built. *Proof-of-concept* is a handy euphemism for putting something together quickly and enthusiastically without too much attention to detail because that would just take too darn long! 

It is still too big and bulky, but it works better than the last build, the stroke length and timing need to be worked with (plenty of adjustability built into this version), as does the cam profile. And the excess fuel volume and air agitation at higher rpm needs to be addressed. So little time and so much to do! Right now I feel like I am just throwing stuff at the wall to see what will stick, but that is fine and I am enjoying it. I hope it is entertaining, or laughable, too.


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## Lloyd-ss (Dec 9, 2022)

*A UNIT INJECTOR THAT FINALLY WORKS.
With Video*

It's been 3 months since I posted in this thread, but a lot has been going on. Especially the number of so-so results.
But I might finally have something. It is a diesel "unit injector", where the pump and injection volume control, and the injector nozzle are all in a single unit, like those used in the old Detroit Diesel 2 stroke engines. It is pumping, and injecting, and there is a plan in place for the fuel volume control, which will be managed by a governor.

I did cheat a little and use the Yanmar nozzle housing (with the holes), but not the needle. All the other parts are mine. It is set up with an adjustable rocker so that the length of stroke and its timing relationship to the fuel inlet port in the pump/plunger body can be fine tuned.  It is fairly fussy about the timing and how much stroke remains after the port is closed. This information should be helpful when it is integrated into the engine.

The test set-up is fairly awkward and the unit injector is only a tiny portion of it. The injection seems to be working well. The nozzle has 4 holes although it only looks like two in the video.


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## Steamchick (Dec 10, 2022)

Video didn't play for me, but "we'll done" on your success.
I understand modern common rail injectors follow a similar principle but with a feed at a few bar pressure, with the injector pumping the high pressure from an electrically powered piezo pump in the body, to give precise metering and timing.
The second part you will need to develop will be an equivalent injector mounted powered pump perhaps?
K2


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## Lloyd-ss (Dec 10, 2022)

The video plays for me. I will try putting in as a YouTube link.

Video added and it seems to work ok.

The injector pressure needs to be increased and shimming the internal spring should take care of that.


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## Lloyd-ss (Dec 10, 2022)

This picture shows a few more details of the unit injector. A low pressure supply pump might be needed, but right now, the gravity feed is sufficient.


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## minh-thanh (Dec 10, 2022)

Hi Lloyd-ss !
Looks great !
  Please update ...


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## Lloyd-ss (Dec 11, 2022)

I tried adding a .010" shim to the internal spring, but I think that used up all of the travel and put the spring into coil bind. Time to take it apart, take some measurements and see if I need to make a new, stronger spring that still has enough travel.


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## Lloyd-ss (Dec 12, 2022)

This is the spring I had to replace. The new spring had to fit around a .078" tube and inside a .148" hole, and used .033 dia wire x .240 long. I still had to grind the O.D. just a tad to get smooth action. AND, it fixed the problem. I will get a picture of the internals next time I take it apart.

The internal parts are already in place to control the volume of each stroke. Adding the external parts (rocker and adjustment and drive pin) will be next. As it is now, it is mainly a single stroke pump with a differential pressure discharge poppet,


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