# Senft "Poppin" engine



## Brian Rupnow (Mar 11, 2018)

I just finished building the latest flame-licker engine designed by Jan Ridder, and my results were not what I hoped for. I did get it to run--long enough to get a video of it running.--But barely. I found it to be an easy build but a very temperamental and difficult engine to run. I don't think this was a result of my workmanship, as I have 25 other self built engines which all run quite well. It may have been my choice of 316 stainless steel for the cylinder. I tried it with a cast iron piston and valve and with a machinable graphite piston and valve, but the performance was no better with either material. I still want a flame licker engine which starts and runs repeatably, and after doing a fair bit of research have decided to build a "Poppin" engine from plans by Dr. J.R. Senft. I will attempt to post my progress and pictures of this engine as it is built.


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## el gringo (Mar 11, 2018)

nice looking model... I've been whittling on one of and on for a few months. I made the conrod of 2024 aluminum in order to eliminate the bearing in the big end, and not have to do the involved built up version as per drawings. The crank is one piece.

Ray M


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## Brian Rupnow (Mar 12, 2018)

If you really squint hard, and use your imagination, you can see the frame of this engine layed out on a piece of 2" x 1" aluminum bar.--Everything has to start somewhere.


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## Brian Rupnow (Mar 12, 2018)

Well jeez, Louise--How many set-ups did you think there were going to be?


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## Brian Rupnow (Mar 12, 2018)

And some more---


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## Brian Rupnow (Mar 12, 2018)

And a few more---


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## Brian Rupnow (Mar 12, 2018)

And considering that there were a couple more set-ups that I didn't photograph, that is a heck of a lot of work for something so small. I planned on making the cast iron cylinder today too, but I have to stop and grab some lunch (It's 3:00 PM here). I don't know if I'll do amymore today or not.


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## Brian Rupnow (Mar 12, 2018)

I can't think of any good reason not to have a sexy cylinder---


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## JCSteam (Mar 12, 2018)

It would be nice to see an alternative design for the cylinder. I was looking at those plans not so long ago and I'll see how yours turns out first.


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## Brian Rupnow (Mar 12, 2018)

The sexy cylinder is under way. Now I have to make a 5/8" expanding mandrel to mount it on so I can turn the radius on the big end.


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## Brian Rupnow (Mar 12, 2018)

Here we have the sexy cylinder finished except for the tapped holes in each end. It is still mounted on the expanding mandrel in the picture.


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## el gringo (Mar 12, 2018)

I like larger diameter on the hot end...is the reason to provide more fin surface for ambient cooling?
Ray M


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## Brian Rupnow (Mar 13, 2018)

Not really--It's a cosmetic thing.


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## Brian Rupnow (Mar 13, 2018)

This morning yielded a cylinder head. Nothing very fancy compared to some cylinder heads I have made, but it should get the job done. How do you like my cylinder?


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## Brian Rupnow (Mar 13, 2018)

Today I made flywheels. I can't even imagine it, but that's a full 8 hours of my time. These flywheels are somewhat unique, because the hubs will be made as separate pieces. Maybe I'll make them tomorrow.


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## werowance (Mar 14, 2018)

Brian Rupnow said:


> How do you like my cylinder?


 
hope that wasn't a trick question  

but I do like the taper a lot.  it just looks unique


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## el gringo (Mar 14, 2018)

I can't believe how fast you build...takes me months, at the least.
btw, will you be using cast iron piston/cyl as per plans?


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## Brian Rupnow (Mar 14, 2018)

Not a great deal done today, as I had a few hours of "real" work. I did however manage a pair of flywheel hubs and their accompanying nuts. (I cheated on the nuts---took a pair from my tool-chest and thinned them down on the lathe.) I have never seen flywheels made this way before, but it seems to work okay.


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## Brian Rupnow (Mar 14, 2018)

el gringo said:


> I can't believe how fast you build...takes me months, at the least.
> btw, will you be using cast iron piston/cyl as per plans?



I have about $100 invested in a stick of 1" diameter x 12" long machineable graphite that I bought to use on the Jan Ridders engine. I will be using it for the piston on this poppin.


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## Brian Rupnow (Mar 14, 2018)

Not a criticism, but an observation. Nothing shows up worse on a model engine than wobbling flywheels. When I make flywheels I generally leave a bit extra on the width and the diameter so that I can mount the finished flywheel on the correct size of arbor and give them a final "dressing" on the lathe to ensure that they are not wobbly as they revolve. Making flywheels with separate hubs that are not in any way "keyed" to the flywheel doubles the effort required to have the flywheels run true on the finished engine.


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## Brian Rupnow (Mar 15, 2018)

I can't swear to this, but my plan to address the flywheel issue is this. I will probably build the cam and cam washer and install them on one of the flywheels, then mix up a batch of J.B. Weld, coat the hubs with it, insert hubs into flywheels put cam and cam washer on one of the flywheels, then run the nuts down tight, and clean up any squeezed out mess. This should make each flywheel assembly a "composite unit". Then after 24 hours I will mount each assembly on a 3/16" arbor, tighten in place with the set-screws in the hubs, then true each flywheel individually. I am not concerned about balance here, just visual "flywheel wobble".


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## el gringo (Mar 15, 2018)

Was there flywheel run-out in the original Senft engines or did he use JB Weld  to help with any fit problems? He mentions perfectly straight alignment using his built up crankshaft. I haven't used JB except in cases of a need for a filler or cosmetics when I didn't feel it critical to function or when I was too lazy to remake the part, maybe I'll  be using it on these built up flywheels. I suppose making them as a monolithic unit would be a pain? 

Ray M


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## Brian Rupnow (Mar 16, 2018)

Ray--In a perfect world, there would be no run out on the flywheels as designed. But the world isn't  perfect place. My lathe has about .003 to .004 total indicated runout. I use a 3 jaw chuck, not collets. That means that every part that I turn on the lathe has the potential to  be .0015 to .002" "out of center". If I mate two independently turned items, they have the potential of having no runout when assembled, or, if it's an unlucky day, they could be at the wrong end of both tolerances and be .003" to .004" out of center. The more turned parts I assemble, the greater the chances become of having enough runout to be visible. Also, the more faces and shoulders there are interacting with one and other, the more chances there are of visible "wobble" from side to side as they rotate. If I do use J B Weld, it wouldn't be to fill holes---It would simply serve to hold all of the assembled pieces together so that by fixturing on the center bore of the hub I can then do the final "trueing" of the assembly in one operation. One flywheel assembly has the flywheel, the hub, and the nut. The other flywheel assembly has the flywheel, the hub, the nut, the cam, and the cam washer (spacer) all assembled together.


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## Brian Rupnow (Mar 17, 2018)

My ball bearings came in yesterday. They are shielded bearings, not sealed. They should turn more freely than sealed bearings because the shields don't really touch the inner race. I may still have to wash the grease out of them in a solvent bath--will know about that later. Today I hope to make the crankshaft.


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## Brian Rupnow (Mar 17, 2018)

So, here we have crankshaft phase-1. Everything is cut to length and Loctited together. The shafts are not "press fit" into the square bars. They are a sliding fit. After 24 hours set-up time I will and pin all the joints with 1/16" dowels (Loctited into place), then wait another 24 hours and saw out the center bit.


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## el gringo (Mar 17, 2018)

Thanks for the explanation Brian. My old 9" 1947 Southbend run about .0015 TIR +- (on a good day). 
I'll shoot for a interference fit and see what happens...then I'll also see how true my one piece crankshaft is.
I wonder, if needed, I could reface the flywheels on the crank in situ? 

Ray M


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## Brian Rupnow (Mar 17, 2018)

I decided not to use any J.B. Weld on the flywheel hubs. That would have been a bit too barbaric, even by my standards. I made the cam and cam spacer this afternoon, assembled everything and tightened it down as much as I dared, then set the flywheels up one at a time on a stub shaft with their hub assemblies in place and "trimmed" the outer diameter and the sides of each flywheel. It didn't take much, but it did take some. Now the flywheels don't visibly run out or wobble.


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## Brian Rupnow (Mar 17, 2018)

This engine has a very interesting big end on the con rod. I haven't built one like this before. The red con-rod is silver soldered to the pale yellow part on the right hand end. The pale yellow part on the right is fastened to the pale blue part on the right with cyanoacrylate glue before any holes are made. Then both yellow and blue parts are tapped all the way through. A bolt is screwed through both parts and tightened. Then the hole is drilled and reamed for the crank journal on the split-line between the two pieces. Then the bolt is removed and the assembly is heated to release the crazy glue.


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## Brian Rupnow (Mar 18, 2018)

This morning I got up and pinned the crankshaft. In a perfect world, I would have drilled the four holes undersize, then reamed them to 1/16" diameter.--In my world, the smallest drill I could find was 1/16" diameter, so that's what I used. In the foreground on top of the vice you can see the four "pins" prepared to go into the holes. The pins are flat on one end and a small taper ground on the other end, and about 1/4" longer than they need to be. First I tried the pins in the holes for fit and yes, they did fit perfectly. Then a small drop of Loctite on each hole, and the pins are inserted pointy side first and brought down until the top of the pin is flush with the side of the crank journal. In the second picture, the pins have been inserted and you can see the extra length extending below the underside of the crankshaft. If the four pins look a bit like welding rod, that's because they are. I can only buy 1/16" rod as "music wire" which is harder than the devil's horn to work with. However, somebody on the forum suggested 1/16" steel, copper coated welding rod, which is perfect for what I'm doing here.


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## Brian Rupnow (Mar 18, 2018)

Have been building a whole armada of tiny little pieces. Valve shaft bushings, valve cross shaft, valve lever arm. I still have half a dozen little pieces to make. I just realized that I polished the wrong side of the cylinder head and installed it backwards. The taper in the center should face into the cylinder, not outward as I have it. The crankshaft does indeed fit into the engine frame but barely.  I had to order a 0-80 die and a 2-56 die, as I need them and don't have them. I downloaded these plans from the John-Tom site, and while the mechanical drawings are clear enough to see, the pictures are horrible. If anyone has built this engine, please post a nice clear picture of where the spring that holds the valve open goes. I can't tell from the stuff I downloaded. I think I will try to build the roller and roller carrier that goes on the end of the valve lever this afternoon and then call it a day.


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## Brian Rupnow (Mar 18, 2018)

I lapped the cylinder this afternoon, but wasn't terribly impressed with the resulting finish on the bore. I used a home made 5/8" lap that I had turned from a piece of aluminum. I had to take a step back and ask myself "Why am I still doing design work for money?"--It was supposed to be money designated for additional tooling in my machine shop. So---I just ordered a set of five barrel laps from KBC. I have one factory built lap that I bought a few years ago for 15/16" bores, and I was very pleased with the results it gave. I ordered a 1/2", a 5/8", a 3/4", a 7/8", and a 1". Sometimes you just gotta spend some money!!


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## rlukens (Mar 18, 2018)

Brian,
I admire your machining and design skills. Having said that, I have to ask: why do you not incorporate your own thoughts into other's designs? I.e. Mr. Senft's frame and con rod...  alternatives are many. Is it because you honor the original designer by following his design to the tee? 
I like to build my own designs, but of course every aspect is "borrowed" from the past. I don't consider that plagiarism.
Just curious.
Russ


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## Brian Rupnow (Mar 18, 2018)

RLukens--Take a look at my post count. Of the over 10,000 posts I have made over the last eight years, roughly a third of them are from my own original designs. However, I try not to claim other peoples designs as my original work. That's not as easy as you would think. There are only so many ways to make a cylinder--a crankshaft--a valve --a cam, you get the idea.  If I seen something that wasn't right or looked like there was a better way of doing it, then yes, I would make the changes. From what I see of Mr. Senft's designs, there isn't a whole lot that needs changing. There are some ideas, such as his con-rod big end that are a bit different, and I like that. After building 25 engines over the last 8 years, I kind of like to do something a different way.


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## Brian Rupnow (Mar 19, 2018)

This morning I finished detailing the crankshaft. I used a pair of "flush cut" wire cutters to snip of the exposed ends of the 1/16" diameter cross pins , then used my monster stationary belt sander to clean up both sides. Before I cut the remaining piece of shaft out from between the rectangular bars, I chucked one end in the lathe and with my dial indicator on the unchucked end I measured 0.016" total runout. This didn't concern me too much, as these small shafts (3/16") are really flexible fliers. I took my rubber hammer and applied it to the shaft until the runout was only .002" total indicated runout. after I cut away the shaft between the rectangular crank throws, I measured again and it hadn't changed any. So---The crankshaft is finished.


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## Brian Rupnow (Mar 19, 2018)

Some very delicate work indeed going on here. This is the arm that operates the valve on the front of the cylinder. The arm is 1/16" thick material. The roller that you can see is 5/16" diameter. The axle inside that you can't see is .175" diameter with a .062 spigot that goes thru the arm.--And the roller has to turn freely after it is all assembled. The plans call for "peening" the head of the 1/16" part which extends thru the arm. I have never had a whole lot of luck with peening one part of an assembly while still leaving the other part free to rotate. I wimped out and silver soldered the projecting 1/16" spigot.---And my roller does spin freely!!


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## Brian Rupnow (Mar 19, 2018)

I'm having to retool my shop just to build this engine. So far I've had to order a #2-56 die, a 0-80 die and a tap, and I've found that nobody in Barrie carries 0-80 hex nuts. I'm working below my comfort level, size-wise, but so far it's coming together well.


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## Brian Rupnow (Mar 20, 2018)

Okay, I'd be the first one to agree, at first glance this looks uglier than original sin. Both brass pieces of the two piece big end have been carved out, one being silver soldered to a 3/32" diameter cold rolled steel rod (which I had to turn from 1/8" steel rod because I don't stock anything that small.) They are currently crazy-glued together and later today I will tap them while still crazy glued together, insert a full thread #2-56 bolt thru all, then drill and ream the hole for the con rod journal. Seems like a very strange way to make a con rod big end, and yet it doesn't require anymore pieces than a  "normal" con rod big end does. It does cut down quite a lot on the "swing radius" of the con rod assembled on the crankshaft.--It is setting on a bigger aluminum block covered with saran wrap so that I don't glue it to the big aluminum block with a couple of 0.015" thick shims under them to maintain alignment .


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## Brian Rupnow (Mar 20, 2018)

Oh wow--Christmas just came at my house!!! The laps that I ordered the other day came in just now. No more screwing around with home made laps. This is very timely, because now I can finish lapping the Poppin cylinder before I make the graphite piston.


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## el gringo (Mar 20, 2018)

"_This didn't concern me too much, as these small shafts (3/16") are really flexible fliers_".

My drawings show a 5/32 crankshaft main, I also had that size bearings on hand, although I thought that was quite small. I carved it out of 1144 stress-proof so maybe I'll get away with it...hopefully my flywheels are true and balanced enough not to flex the crank. I can see the headlines now, {cat is injured when chased by flywheel that  broke off  work hardened crankshaft while running engine at high RPM}:hDe:


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## Brian Rupnow (Mar 20, 2018)

The con rod big end does look okay now that it is finished and fitted. I have never made one this way before, so it was a new experience. If you really, really need radial clearance around the crankshaft, then this is probably a good idea. I don't particularly care for this method, as your options are very limited for any kind of adjustment. At any rate, it seems to work, and I've managed to do something "just a little different".


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## Brian Rupnow (Mar 20, 2018)

El Gringo--I decided to use a 3/16" crank because I already had some 3/16" cold rolled steel and I had to buy bearings anyways.


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## Brian Rupnow (Mar 20, 2018)

I used one of my new laps to lap the bore of the cylinder. I only used a single stage of lapping using 600 grit paste. This isn't perfect, but it's good enough for what it will be doing. To be perfect, I would have used grit in three successive stages, using #300 first, then stepped up to 400, then up to 600. There's a little story that goes with this. When I first started machining eight years ago, I bought a number of new, expensive reamers. They would ream a bore and leave it almost flawless inside. Over the years, the reamers have grown more and more dull, not leaving a perfect finish anymore, but that was okay--My 3 stone brake cylinder hone would clean up any imperfections prior to lapping. But--On a cylinder with a 5/8" bore, the hone will not fit into it. The finish after reaming did have scratches and flaws in it, and I had no good way to clean the bore up. I have been contemplating buying a set of expanding laps for a few years now, and this seemed to be the time. I will still probably shop for a smaller diameter hone, but for now the lap has cleaned things up sufficiently. Another factor in all of this is that on all of my i.c. engines, I have been using Viton rings, which are very forgiving of surface finish. If the surface finish isn't perfect, it will be after running for an hour.--The Viton rings will polish the inside of a cast iron cylinder to a mirror finish in about an hours running.-You might have to replace the ring after that first hours running, but Viton rings are cheap.


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## Brian Rupnow (Mar 20, 2018)

I bought a new #2-56 die today to thread the ends of the cross shaft that operates the valve. I have no idea what happened, but after threading down to the shoulder of the shaft and then backing off (by hand), the diameter of the shaft was decreased but no threads were on it. Very puzzling. Then I ran a #2-56 bolt thru the die, and it matched the threads just fine. Then I ran a #2-56 nut down the same bolt and it threaded okay. I had the shaft ends turned to .085". A mystery, and now I have to make a new shaft.


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## el gringo (Mar 20, 2018)

Brian Rupnow said:


> Oh wow--Christmas just came at my house!!! The laps that I ordered the other day came in just now. No more screwing around with home made laps. This is very timely, because now I can finish lapping the Poppin cylinder before I make the graphite piston.



You have made  an excellent choice and your lapping life will be a much happier experience...I would suggest you store them vertically.


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## el gringo (Mar 20, 2018)

"El Gringo--I decided to use a 3/16" crank because I already had some 3/16" cold rolled steel and I had to buy bearings anyways. "

In any event I believe the 3/16 shaft was the better choice.
Ray M


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## deverett (Mar 21, 2018)

Brian Rupnow said:


> Oh wow--Christmas just came at my house!!! The laps that I ordered the other day came in just now. No more screwing around with home made laps. This is very timely, because now I can finish lapping the Poppin cylinder before I make the graphite piston.



Acrolaps barrel laps are excellent tools.  Now you have the arbor and adjuster, it is quite easy to make your own custom size laps. 
 See http://www.homemodelenginemachinist.com/showthread.php?t=26387&page=3  Reply 30.  I've also made a new arbor/adjuster for other sizes of lap.  

Living where you do, it may not be worth your while making new laps; 'off the peg' laps may be cheaper than the brass required to make them.

Dave
The Emerald Isle


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## Brian Rupnow (Mar 21, 2018)

This morning I have decided to put on my design engineers hat. Mr. Senft did a marvelous job on this engine, But---there are a couple of spots that I see as potential problems. The 1/8" diameter cross shaft which operates the valve was originally designed as having the ends turned down to .085" and threaded #2-56 and the flat arm with the roller on it was sandwiched between the nut and the shoulder on the shaft. There was no key of any kind to make that arm hold it's position, and as expected, it slips. I have been warned of this by my own experience on similar mechanisms and by Nick, a gentleman who has successfully built and ran one of these engines. Yesterday when I tried threading the ends of the rod I had made with a new #2-56 die I had just purchased, it screwed up the end of the shaft and didn't leave any thread??? So--this morning, a redesign. The cross shaft now has plain ends with no turn down. The plate "arm" how has a hub with two #5-40 set screws holding it in position on the shaft. The far end of the shaft which originally held a spring clamped between two hex nuts will receive a similar treatment with a hub and set-screws holding the spring.


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## Brian Rupnow (Mar 21, 2018)

I like that valve arm a lot better now. I added a hub with two set screws to the arm and made a separate hub for the end where the spring goes. I have also finished the brass part that bolts to the graphite piston. In fact, the only thing i have left to do is make the graphite piston and then reassemble everything.


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## el gringo (Mar 21, 2018)

Brian Rupnow said:


> So, here we have crankshaft phase-1. Everything is cut to length and Loctited together. The shafts are not "press fit" into the square bars. They are a sliding fit. After 24 hours set-up time I will and pin all the joints with 1/16" dowels (Loctited into place), then wait another 24 hours and saw out the center bit.



Do you use the different Loctite products for the different applications; slip fit, press fit, wicking grade permanent thread lock, medium thread-lock  etc? 
Ray M


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## Brian Rupnow (Mar 21, 2018)

No, I use 638 for everything. It's expensive as Hell, but it works for everything.
I haven't had time to stop and sort out the die, but I will get to it eventually. I finished the graphite piston, and got a good "sizing" on it. The last couple of thou. were taken off using the back side of my 280 grit sanding strips.


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## el gringo (Mar 21, 2018)

I will try '638'...I use  242,620,290 &  603...they are all expensive, I could save a bunch...I like the  290 thread locker for  its 'wicking' capabilities to allow application after components are tightened in place. 

BTW I thought I was unique by using the backside of the sandpaper for final graphite polishing .:thumbup:

Ray M


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## Brian Rupnow (Mar 21, 2018)

I was mistooken---Got everything back together and then realized I still had to make the valve rod and the valve itself. The engine turns very freely through half of it's rotation, and has a bind in the other half. Tomorrow I hope to get the "bind" sorted out and make the last two pieces.


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## Brian Rupnow (Mar 22, 2018)

So here we are at the almost last stage. Loosening the engine up to absolute minimum friction. If an engine has a slight bind on part of the full 360 degrees of rotation, before I start tearing things down I try this. About 80% of the time, it works. I like to let he engine run for an hour or hour and a half. at around 400 rpm. if the bind isn't gone in an hour and a half of running, then something mechanical is out of whack, and the engine will have to be torn down and "sorted".


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## Brian Rupnow (Mar 22, 2018)

This morning I've been experimenting with my new dies. I have a #0-80 die for threading 1/16" diameter stock and a #2-56 for threading 0.085" stock. On first try, neither die would take hold and start cutting threads. I then forced them to start with lots of pressure, and they threaded about 3/8" of stock before I backed them out. They did an amazing job of cutting the 1/16" and 0.085" stock down to a smaller size, but left no thread. I then tried putting a slight taper on the end of the stock, and tried again.---Same results!!! I've never had a problem threading stock before, but I've never threaded anything this small. Next step was to use the tiny little screw in the die to open the die up a little. This did work, and I have achieved some pretty respectable threads in 1/16" stock.--Of course I don't have any nuts to try on my newly created 0-80 threads--they are supposed to arrive here tomorrow. The 0.085" diameter for the #2-56 thread is not a size I stock, but I will turn some stock and try it again with the die opened a little. (I do have #2-56 nuts on hand to verify if this will work for the #2-56 threads.)


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## Brian Rupnow (Mar 22, 2018)

The last time I saw nuts this size they were on a Bumblebee!!!


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## Brian Rupnow (Mar 22, 2018)

I'm not exactly forging ahead, but I am making progress. The engine has loosened up nicely after an hours running. I think I've figured my dies out now, at least I have them cutting threads that the store bought nuts will fit onto. I have a temporary base bolted to the engine at the moment, as there is no way to hold the engine down without an auxiliary base. I have to figure the spring out next that holds the valve open (the cam closes it.)


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## el gringo (Mar 23, 2018)

Brian Rupnow said:


> I bought a new #2-56 die today to thread the ends of the cross shaft that operates the valve. I have no idea what happened, but after threading down to the shoulder of the shaft and then backing off (by hand), the diameter of the shaft was decreased but no threads were on it. Very puzzling. Then I ran a #2-56 bolt thru the die, and it matched the threads just fine. Then I ran a #2-56 nut down the same bolt and it threaded okay. I had the shaft ends turned to .085". A mystery, and now I have to make a new shaft.



When cutting threads to a shoulder with these smaller split dies use the other side of the die to start. If you look closely at the apparent starting side you will see no threads in the opening that is probably smaller than the shoulder diameter you are threading against causing a rough diameter reduction cut .


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## Brian Rupnow (Mar 23, 2018)

When cutting threads to a shoulder, I start the thread with the correct side of the die facing the work and thread as far as I can. Then I back off of the part, reverse the die, and thread again right up to the shoulder.---Brian


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## Brian Rupnow (Mar 23, 2018)

Just a quick and dirty scrawl this morning to see what things would look like with a base and a burner.


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## Brian Rupnow (Mar 23, 2018)

Where do I get a piece of 0.020" diameter spring wire? I'm thinking guitar string---maybe?


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## fcheslop (Mar 23, 2018)

Model aircraft guys use it Piano Wire 24g or beg an espresso machine filter holder spring clip from youre local coffee shop
Or been a tight wads I straightened a spring out and used that bit of wire


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## Brian Rupnow (Mar 23, 2018)

I worked in my office across town today, and managed to score a piece of .002" shim stock for the valve and a piece of 0.026" spring wire that should get the job done.


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## Brian Rupnow (Mar 23, 2018)

There is definitely a degree of "Hinky" to the valve mechanism on this engine. I have hidden one flywheel here to show the "hinkiness" a little better. The angular relationship between the lever with the roller on it and the small 1/16" diameter rod holding the 0.002" thick valve is adjustable.  When the roller is fully "on the cam", the 1/16" diameter rod should be positioned so that the .002' thick valve just covers the hole in the cylinder head and overlaps the edge by about 0.015".--It doesn't in this picture--That was just me placing the 1/16" rod in a perfectly horizontal position when the roller was up on the cam. As you can see, the valve doesn't come close to covering the hole. I can sort out what the angle SHOULD be tomorrow. Then after establishing the correct angle, I have to establish exactly WHEN this event should take place in the cycle of the piston moving in the cylinder. Dr. Senft states that ideally, "Choose a direction of rotation and initially position the cam/flywheel on the crankshaft so that the valve closes the port when the piston has completed about 85% of it's outward motion, that is about 45 degrees before outer dead center."-I've never had so much fun with my clothes on!!


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## Brian Rupnow (Mar 24, 2018)

I arose from my warm and comfy bed this morning and decided that this would be the day to build a proper engine base and start on a burner. Everything worked, everything fit, and now I'm off to a nearby coffee shop for some lunch. Goodwife has taken #2 son to #1 daughters house in Orangeville to repair a garage door, and I am left to amuse myself for the day. After lunch I will decide whether to finish the burner or set it aside and see if I can start the engine on a "borrowed burner" from another project.


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## Brian Rupnow (Mar 24, 2018)

With no nuts on the cross shaft, I had to resort to a little "engineuity" to make a hub that will hold the piece of spring wire to spring-load the cross-shaft to close the valve. I just finished this part, and it's true--the smaller the part is, the more difficult it is to make.--I would have never made it as a watchmaker!!!


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## Brian Rupnow (Mar 24, 2018)

Enough for today. I have the .002" thick valve installed and have set the angular relationship between the valve roller arm and the 1/16" diameter rod that controls the valve. I have "timed" the engine correctly (I think). Senft says to choose a direction of rotation and set the timing so that the valve closes at about 45 degrees before the piston is at "outer dead center".--That confuses me. I have always worked in terms of "bottom dead center" and "top dead center". if anybody would like to clear that up for me, please do. The engine quacks like a duck if I spin the flywheel quickly by hand, so I think that is a good sign. It means that the vacuum in the cylinder as the piston moves towards bottom dead center is pulling the .002" thick valve totally closed.


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## Cogsy (Mar 24, 2018)

Brian Rupnow said:


> That confuses me. I have always worked in terms of "bottom dead center" and "top dead center". if anybody would like to clear that up for me, please do.


 
'Outer' dead centre is just top dead centre but in a horizontal orientation there is no top or bottom as such. So it's outer (away from the crank) and inner (closer to the crank). Just a bit of outdated nomenclature.


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## Brian Rupnow (Mar 25, 2018)

This morning I made a top for the alcohol burner but haven't soldered it on yet. I ordered a set of six 1/8" diameter wicks from Amazon, and I don't want to make the spout that holds the wick until I have the wicks in hand. I've also been looking at what happens with the engine timed the way I have it. When the cylinder is sticking out to the left, I want the flywheels to rotate clockwise. (This keeps from having to run my hand thru the flame after I've flicked the flywheel.) So--piston is at top dead center and valve is wide open. I start rotating the flywheel clockwise. Thru the first 45 degrees of rotation the valve stays open, sucking in flame. During the second 45 degrees of rotation the valve begins to close but hasn't fully closed yet. Thru the third 45 degrees of rotation the valve closes completely. During the last 45 degrees of rotation the valve remains closed and the piston reaches bottom dead center. In the next 45 degrees of rotation as the piston begins to be sucked back up towards top dead center, the valve stays closed for about the first 22.5 degrees, then begins to spring open and by the time it reaches 45 degrees the valve is fully open. The valve then remains open right on thru the top dead center piston position and doesn't close again until the whole cycle repeats itself.


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## Brian Rupnow (Mar 25, 2018)

I couldn't wait any longer. I had to see if this thing was going to work or not. I have the base cobbled together with a spacer between the base and the engine in order to get it high enough to use the burner from one of my other engines. I kept trying different timing settings until I worked all around the clock and came back to my original setting. I had to tweak the .002" valve a couple of times to ensure that it actually closed the hole in the cylinder head completely, and away it ran. I am feeling Oh so Good about this.
[ame]https://www.youtube.com/watch?v=RhrbGjgaaEk&feature=youtu.be[/ame]


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## Brian Rupnow (Mar 25, 2018)

During my build, someone suggested that I make two cylinder heads.--One as per the original plan, and one that looked like this. Same thickness, same bolt holes, a plain 1/4" hole in the center, and a 0.030" deep slot 0.020" wider than the 0.002" valve plate which seals and unseals the cylinder. This head would bolt right over top of the original cylinder head, and prevent the valve from falling to one side or the other and not covering the hole properly.--I see now that this is a very real possibility, as either the two #0-80 nuts don't hold the valve solidly enough to prevent it, or else the 1/16" diameter rod unscrews itself a bit from the cross shaft. I think this is probably a good idea, and will incorporate it into my build.


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## Ghosty (Mar 25, 2018)

Brian,
Congrats on a runner, will be watching to see what you do next

Cheers
Andrew


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## Johno1958 (Mar 25, 2018)

Very nice Brian congrats.
They would be good on the desk top to run as I guess there wouldn't be much
odor ?
John


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## Brian Rupnow (Mar 25, 2018)

No odour, but there is an open flame. I really can't speak yet on the dependability or repeatability of this type of engine. I really don't know yet if once everything is sorted whether they start and run every time you want, or if there is a lot of fiddling to get them to run.---Brian


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## el gringo (Mar 26, 2018)

You've done it again Brian, two engines and I haven't even finished one. Well done.!!!!!
Ray M


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## Cogsy (Mar 26, 2018)

Congrats Brian, seems like a very good runner. Yet another one to add to the wish list I guess.


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## el gringo (Mar 26, 2018)

non sequitur; I wonder what two of those little guys would sound like would sound  like running nose to nose on a common flame, one 180 deg out... might even be able to rig a common valve?? 
Ray M


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## Brian Rupnow (Mar 26, 2018)

Blogwitch has built a twin. It's on here somewhere.


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## ShopShoe (Mar 26, 2018)

Congratulations on a runner Brian.

I like the modified cylinder head idea and will be waiting and watching for it.

I also like the shape of the cylinder.

--ShopShoe


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## Brian Rupnow (Mar 26, 2018)

I had to go to court this morning for jury duty selection. Sat around for 3 hours with about 60 other people waiting and then we were told the case had been dismissed and we were all excused. I came home this afternoon, built a 1/2" spacer block to go between the engine and the base and mostly finished a burner for it. The burner needs a tiny bit of "fettling" but it was progress.


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## Brian Rupnow (Mar 26, 2018)

When I put the 1/4" deep counterbore in the base to hold the alcohol burner, I put in a smaller diameter and 0.130 deep counterbore in the center to hold a rare earth magnet. The burner body is made from mild steel, and the magnet is epoxied into the small counterbore. This will keep the burner from moving around when I run the engine. I have also given a bit more thought to the double cylinder head to guide the .002" valve. Since the valve only needs guidance in one plane, I may just make a new thicker cylinder head with the valve groove cut into it. The current cylinder head is 1/16" thick. If I made a new one 1/8" thick this would allow a 1/16" deep groove, which would be sufficient to do what I want.


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## el gringo (Mar 27, 2018)

I saw one running (somewhere on this forum) with the two head design and it seemed to do well. I wonder if a thicker valve leaf could be used as well.

On the subject of the Senft cylinder head; I found mine to be leaking.
My 'test' method was to hold a finger on the port as checking the piston fit.
When the piston was pushed toward tdc  it slowly crept forward due to losing compression (which it did not do during the same 'test' by covering the end of the cylinder without the head installed)  . When tested with the cylinder head under water the leak was obvious.  

My fix was Loctite # 518 'gasket eliminator' for aluminum flanges. It is not an adhesive and is easily removable. I have been using it out of the same container for ~ 15 years...some shelf life

Ray M


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## Brian Rupnow (Mar 27, 2018)

I have had a frustrating and dreadful day. My Poppin ran yesterday long enough to get a brief video, and I haven't been able to get it to run again since. I have spent an entire day screwing around with this thing, but no joy. I also found the answer to that age old question "Will a 1/8" wick fit down a 1/8" i.d. tube.--OF COURSE NOT DAMMIT!!! That would have been too easy. I need to get away from this thing for a few days, and I just got a couple of emails about some "real" work, so I'm going to leave this set for a couple of days, before I start banging my head on a rock!!!


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## el gringo (Mar 27, 2018)

Brian, check the cyl head for a leak.... " On the subject of the Senft cylinder head; I found mine to be leaking.
My 'test' method was to hold a finger on the port as checking the piston fit.
When the piston was pushed toward tdc  it slowly crept forward due to  losing compression (which it did not do during the same 'test' by  covering the end of the cylinder without the head installed)  . When  tested with the cylinder head under water the leak was obvious."...

Also, did you try the previous flame arrangement?


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## Brian Rupnow (Mar 28, 2018)

El Gringo--Last evening after reading your post, I did use a Loctite  silicone gasket maker to seal my cylinder head.


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## Brian Rupnow (Mar 28, 2018)

In trying to make an analysis of why I couldn't get the engine to run yesterday, I can think of only a couple of things. I know the timing is correct, because after my first successful run I match marked the flywheel/cam and the crankshaft so I would always be able to find my way back to that position. The only other things that can cause this engine not to run is that either the .002" valve is not sealing the hole in the cylinder head totally, or the machinable graphite piston is worn down to a point where it is not sealing. I don't really know much about machinable graphite but it does seem very soft. I may make a new piston from cast iron. I spun those flywheels  at least 100 times yesterday, with no joy. The most unusual thing was that there was no where at all that the engine picked up a little bit or tried to run. That is quite noticeable when you hit the "sweet spot". I have to also rework the new dedicated burner because the 1/8" wick which came yesterday won't fit down the tube I have soldered into the top of the tank.
EDI--EDIT---
No, it isn't the piston worn down. I just rotated the .002 valve out of the way and tried to rotate the engine with my thumb held over the hole in the cylinder head. My thumb over the hole prevents the engine from turning freely. I can feel the suction and compression.


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## Brian Rupnow (Mar 28, 2018)

In case you missed it--I had to change the alcohol burner wick tube. It didn't work as well as I thought it would. I had to open the bore of the wick tube up to about 0.153" so I could persuade the 1/8" wick to go into it, and it didn't seem to work very well with the tube running all the way to the bottom of the tank like I had shown it in a previous post.  So--I cut the wick tube off just under the top. Lesson learned--I'll know better next time.


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## Brian Rupnow (Mar 29, 2018)

Today we have one small success to feel good about. I reworked the alcohol burner as per the newest drawing posted, and it appears to work like a charm. I am running 99% medical alcohol in the burner. The flame looks very large and very yellow, but that may just indicate that I need to trim the new 1/8" wick. I see a few videos on YouTube where the flame is mostly blue and has very little yellow corona. I wonder what those guys are burning? I also picked up some 0.003" material to make a new valve.


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## Brian Rupnow (Mar 29, 2018)

Well, I guess I have to acknowledge that my butt has been kicked on this one. I've tried everything I know how to do, and no good results. Timing is good, flywheels are free to spin, and the flame is good but no joy. I've tried pre-heating the cylinder but it doesn't make any difference. This is very unusual for me, but for now, I'm whipped.---Brian


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## Brian Rupnow (Mar 29, 2018)

I have watched about a hundred videos of Poppin engines in the last week. In a number of cases, the spring which holds the roller in contact with the cam is a tension spring connected to the 1/16" diameter arm which supports the valve. It runs vertically from the arm down to a screw tapped into the sub base. This is not what Dr. Senft calls for on his drawings of this engine. I'm curious as to why people do this. Does it put less load on the flywheels? Does it make the engine spin more freely? Is it part of a set of plans similar to Dr. Senft's?--Or is it just that some guys had a tension spring and not a piece of 0.020" music wire to make a spring like Dr. senft calls for?


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## ninefinger (Mar 29, 2018)

Brian,

don't make the spring too strong, one of the unwritten items on the Poppin is that the vacuum holds the valve shut as long as it need to be with a weak spring, too strong and it opens prematurely reducing the effectiveness of the engine and / or making it hard to run. This is why the timing on a Poppin is usually not critical- the exhaust timing is somewhat self regulating and you are only really controlling the intake closure.

Mike


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## Cogsy (Mar 29, 2018)

From what I understand, isopropyl alcohol (likely your 'medical grade') does not burn as hot as denatured alcohol (ethyl alcohol) and your running issues may be as simple as that. I use methylated spirits which is about 96% ethyl alcohol with a dash of methanol to make it undrinkable. Burns nice and blue, with or without a wick.


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## fcheslop (Mar 30, 2018)

Assuming you are using the same fuel when it last ran. I cannot see how it would be a problem
The spring only needs enough tension to keep the follower in light contact with the cam anymore and you are wasting some of the little energy it makes. It wont make any difference to the type 
One though comes to mind as youve changed the valve simply make sure in the closed position there is very little overlap as it alters the timing if theres to much. It should only need to cover the port by a 1/64 or less
If the valve is to thick it will prevent adequate exhausting although Iv used 4 thou and prefer to use feeler gauges the metal just seems that bit better
The cylinder head with the groove in for the valve will make it crack very quickly as I found out on my second Poppin
Out of curiosity have you or anyone else come across the water cooled drawings Iv been looking for years to no avail
Well thats my two bobs worth
cheers


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## Blogwitch (Mar 30, 2018)

Frazer,

The only ever water cooled one I have come across is the large Gert Litty # VST 45, which as far as I can remember I sent you the plans for a while back.

Brian,

The fuel that I used for flamelickers was the same as the one Cogsy uses, it burns with a clear light blue flame. I also used industrial methylatd spirit which is basically the same as the purple couloured meths you can buy in the shops over here except it is clear and doesn't have the anti drinking ingredient.
I have also tried using gas to very good effect on my Jan Ridders double one and also this one, a Scott, which is destined to become finished in the near future. The only problem with the Ridders one is that it started to carbon up after about 10 minutes, maybe because I didn't make a clean enough burner, just a hole in tthe end of a pipe, but it did run well on it.

[ame]https://www.youtube.com/watch?v=Mi_T60n52jg[/ame]


John


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## Brian Rupnow (Mar 30, 2018)

The sun is shining---the birdies are singing--All is well at the Rupnow house!!! I finally got my Poppin to run the way I wanted. What did I do to make this happen?  First of all I disconnected the valve mechanism completely and removed the con rod and piston. A flip of the flywheels would only make them run for about 15 seconds.---What?--That can't be right. I loosened off the two #2-56 bolts that clamp the straps on top of the bearings and tried again. Flywheels would now spin for over 60 seconds. I remounted the con rod and piston, and then the flywheels would spin for about 12 seconds. I remounted the valve mechanism and a flip of the flywheels would only make it free-wheel for about 3 to 4 seconds. I wasn't happy with the piece of 0.026" spring wire I had mounted as per Dr. Senft's instructions. (actually he called for 0.020" spring wire, but I was only able to get 0.026") I made up a hub for the "off" side of the cross-shaft and hooked up a very light tension spring to replace the .026" spring wire. At first the tension spring was too weak to totally open the valve, but I kept cutting off coils until it was just strong enough. that seems to have done the trick. Engine fired right up as you see in the video. I don't know what the honking and squealing noises are, but I put that down to the 0.002" thick valve. I don't care if it honks a bit.--I've got a runner!!!!!
[ame]https://www.youtube.com/watch?v=UXn6zJBG1h8&feature=youtu.be[/ame]


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## el gringo (Mar 30, 2018)

"If the valve is to thick it will prevent adequate exhausting although Iv  used 4 thou and prefer to use feeler gauges the metal just seems that  bit better"
Would be interesting to know if anyone out there has tried heat treating shim stock to stiffen it up a tad? When I heat it to a high blue, ~ 600 f, it seems to stiffen but warps because I don't have a controllable heat source. 

Ray M


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## Brian Rupnow (Mar 30, 2018)

Ray--If you want stiffer shim stock, cut up a set of feeler gauges. I have had a bit of a chance to calm down since this mornings run, and set the engine up on an old textbook . That cuts down on a lot of the noise generated by the desk it is setting on (Like an echo chamber). The audio pickup on my camera is super sensitive, the engine runs much quieter than it sounds in the video. Most of the honking and squealing sounds have gone away.
[ame]https://www.youtube.com/watch?v=frwkskWA1ZU&feature=youtu.be[/ame]


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## el gringo (Mar 30, 2018)

Brian Rupnow said:


> the engine runs much quieter than it sounds in the video. Most of the honking and squealing sounds have gone away.
> 
> The appraisal of the  honking and squealing sounds belong in the domain of the eye of the beholder....:hDe:
> 
> ...


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## Brian Rupnow (Mar 30, 2018)

So, Ray--are you building one of these, and if so, what stage are you at?---Brian


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## ShopShoe (Mar 31, 2018)

Brian,

As always, I knew you'd get there. That is a pretty and pretty-well-running engine.

Congratulations and thanks for posting the whole build thread.

--ShopShoe

P.S.:  If I don't get around to building a whole one of these engines someday, I might copy just your tapered cylinder: I like the look of it.


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## el gringo (Mar 31, 2018)

Yes Brian, I am starting to mess with the valve & timing... any day now I'll put the fire to it.


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## Brian Rupnow (Mar 31, 2018)

Some of the flame eaters I seen on you-tube (Big Nick for example) have exhaust stacks on the cylinder. What's that about? Has anyone knowledge of why. Obviously it must help from blowing out the flame, but I would like some more information. Thank you in advance, Brian


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## el gringo (Mar 31, 2018)

Brian Rupnow said:


> Some of the flame eaters I seen on you-tube (Big Nick for example) have exhaust stacks on the cylinder. What's that about? Has anyone knowledge of why. Obviously it must help from blowing out the flame, but I would like some more information. Thank you in advance, Brian


Cosmetic?


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## Brian Rupnow (Mar 31, 2018)

No, not just cosmetic. They do help the engine run. I'm not certain yet how they work, but I'm getting replies on other forums saying the help the engine to run more stably.


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## rlukens (Mar 31, 2018)

Brian Rupnow said:


> Some of the flame eaters I seen on you-tube (Big Nick for example) have exhaust stacks on the cylinder. What's that about? Has anyone knowledge of why. Obviously it must help from blowing out the flame, but I would like some more information. Thank you in advance, Brian



I'm interested in that too. I assume that the "vacuum" in the cylinder changes to pressure somewhere mid stroke. The exhaust port is basically a check valve that relieves that pressure when the intake valve is partially close. Makes sense to me.


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## fcheslop (Mar 31, 2018)

It is a relief valve for the exhaust gasses instead of blowing the valve of the port
You can see it clearly on this Bengs video just a nitrile ball that shuts off on a seat like a clack valve.
You adjust the amount of lift on the ball to regulate speed.This system is used on a lot of flame gulpers including the lanz Bulldog
https://youtu.be/0G4OuBVb7NY


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## Brian Rupnow (Mar 31, 2018)

Ohhh--I do like that!!!


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## fcheslop (Mar 31, 2018)

I plan on building one with a 50mm bore once Iv finished other projects
well thats the plan
There is a lot of flamefesser designs knocking about mainly European 
Here is a link to the build of the kit
http://www.bengs-modellbau.de/magazin/2988-baubericht-flammenfresser-jarne/
cheers


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## el gringo (Mar 31, 2018)

"So, Ray--are you building one of these, and if so, what stage are you at?---Brian"
Did you receive the answer to your query?

               __________________


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## Brian Rupnow (Apr 1, 2018)

Yes Ray, I did. It looks as if you are pretty well finished. If anyone liked my sexy cylinder, here is the drawing of it.--Brian


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## Brian Rupnow (Apr 1, 2018)

I got an answer on the poppet valve exhaust. There should never be positive pressure build up inside a flame eater engine. The Poppin gets away without an exhaust stack because if the piston moving towards top dead center causes any positive pressure, the .002" thick valve flexes enough to release this pressure. On larger flame eaters where the sliding valve is mechanically driven and does not flex, you need the exhaust valve which is indeed a poppet valve to release this pressure. This type of valve is basically a small ball setting in a cone. It will let pressure out, but seals automatically when the piston is creating suction to pull the flame into the engine. Some engines have a stack, although it is just for show. Other engines just have the exposed valve setting on top of the cylinder at the end opposite to the crankshaft.


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## rlukens (Apr 1, 2018)

fcheslop said:


> I plan on building one with a 50mm bore once Iv finished other projects
> well thats the plan
> There is a lot of flamefesser designs knocking about mainly European
> Here is a link to the build of the kit
> ...



That is a fantastic little engine. I know now whose design I'm going to follow.
I notice there was little attention given to reducing moving mass and I don't think I saw any bearings. Yet it took off with a twist. 
Thanks for posting

Russ


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## Brian Rupnow (Apr 5, 2018)

What a lovely little engine this is. The more it runs, the better it runs. I fire it up a couple of times a day when I'm setting at my computer and it makes me smile. No need for a battery or an air compressor. This engine is pure fun!!!


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