# Boll Aero - my first engine build



## Roboguy (Nov 6, 2015)

In my introductory post I said I would be starting my Boll Aero build shortly. Well it's taken me a week or so to get under-way, but I finally got started last night.

I have minimal equipment at this stage, and I chose the Boll Aero due to the low part count, and the fact that it can be built entirely with a lathe and a drilling machine. I have a Myford Super 7 lathe and a very budget drilling machine (lesson learned there!) and am slowly amassing the requisite hand tools, drills, taps, dies, reamers etc.







I've spent quite a bit of time already thinking through the machining sequences and how I will hold work pieces. I've written up a series of steps for the first three parts I plan to machine. Those being the crank case, the backplate and the main bearing (nose piece).

One challenge I have been grappling with is how to accurately drill the holes in the three parts given I don't have a mill and my drilling machine is a bit rubbish. The plan I came up with was to make a drilling jig that I would use to position the holes in all three pieces so the line up correctly.

To that end I started with a hole guage for the main bore. This will be used to locate the jig over the crankcase for drilling. This was the first time I had ever used my four jaw chuck. I made the tool post mount for the dial indicator as I thought that would be useful when it comes to squaring up the crankcase and other parts soon.

Turning up the hole gauge





Marking out the drilling jig





First time boring in the lathe!





Testing with the hole gauge





I used the point of the knife tool to scribe the PCD to locate the mounting holes on





And this is where I finished for the evening





So I just have drill the mounting holes in the jig tapping size so that I can spot drill through it later. 

I am going to remake the hole gauge as I screwed up and overshot so that it is now 0.02mm undersize and so is a bit loose in the hole in the drilling jig. According to my digital calipers that is the correct bore size.

Next up the crankcase.


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## edholly (Nov 6, 2015)

Roboguy,

Congratulations, the BollAero is a wonderful engine to start with. I too made that as my first engine and there has been a few more since then.

If you don't have a good Mill, then marking out is crucial and one trick I have learned is to use a simple sewing needle, put it in a drill and as the drill rotates bring the point up to a grinding wheel. In moments you will have the sharpest needle ever, even slightly blued on the end, but when used for marking out in alloy, you can get an accuracy down to almost a thou.

When it comes to your piston and bore fit, I will help you with the process I learned from David Owen, a process that almost guarantees great compression, the secret to a good diesel.

I will watch with interest your progress ... Ed


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## Herbiev (Nov 6, 2015)

Great start to a great engine. Looking forward to next instalment


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## quinette7 (Nov 6, 2015)

Roboguy -

Good start!  First engines always present quite a few problems. Your photos give a good sense of how you are solving them.

Bob
Salt Lake City


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## 10K Pete (Nov 7, 2015)

Off and running! Don't worry about the exact dimensions all the time.
Many of the mating fits will be adjusted to fit as you go. If you make the
bore, for example, .05mm to big then you make the piston bigger to fit.
Those little adjustments we can do when building one-offs and no one
is the wiser except you. And us if you tell us!  

Keep on goin'.

Pete


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## Roboguy (Nov 7, 2015)

Thanks very much for the encouragement everyone!

Ed, I'm definitely interested in any tips for the piston and bore fit. Several others have pointed out this will be one of the most critical aspects of the engine.

Apologies if I show stuff most others would skip out. Before I started I looked around for a Boll Aero build thread and  couldn't find much, so I'm hoping that if I do a decent job of documenting my own progress it might be useful to others - especially first time builders like me. 

Also, apologies for the mixing of units between imperial and metric! I am working from imperial drawings with an imperial lathe, but all my measuring equipment is metric and being from New Zealand metric are my "native" units.

So, some more progress has been made!

I started by cutting some 1" square aluminium to length + a few mm to allow for squaring up the ends. I then chucked this up in the four jaw and faced the first end.






Next, I removed it from the chuck, marked out the exact length 46.86mm (1.845"). I also marked of the amount to chamfer on the top corners of the crankcase. Back in the four jaw this time with some alloy shims (made from an old coke can) to protect the work piece. I used my tool post mounted DTI to ensure that the work piece was exactly centred. 






Setting things up in the four jaw chuck isn't anywhere near as difficult as I had feared. It requires a bit of faffing about, but I plan to make a second chuck key in the near future and that should speed things up.

I centre drilled and supported the work piece with a live centre while I chamfered the corners. The tail stock centre probably wasn't required, but due to the interrupted cuts that were going to be required to chamfer the corners I thought it prudent to provide some extra support to avoid the work piece slipping out of centre.

Finally I enlarged the central bore using a succession of drills ready for the boring bar. 






And that's where I finished for the day, ready to bore to size for the cylinder.


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## edholly (Nov 8, 2015)

OK Roboguy,

Here is my BollAero .. about a couple of hours running now on 2nd piston/cylinder combination after David Owen showed my me how to get a great fit with these components. Video is of one stopping and restart with 1 flick - did this 10 consecutive times !  A wonderful first engine to build .. here running a 10 x 4 wood Turnigy prop at around 5300rpm

[ame]https://www.youtube.com/watch?v=GGVX159QPr4&feature=youtu.be[/ame]


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## Roboguy (Nov 9, 2015)

Awesome, thanks for posting this. That certainly gives me something to aim for! 

It's very humbling when you start building your first engine. So many of the things that other people make look so simple are suddenly quite a challenge, and even just figuring out how to start is difficult sometimes.


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## Roboguy (Nov 10, 2015)

Over the last couple of evenings I've managed to make some more progress. The next step was to bore out the crank case for the cylinder. Before doing that though I realised I should have made a hole gauge for that bore as well. I don't currently have an inside micrometer or telescopic gauge, so a hole gauge that has been turned to exact size is the next best thing.

To avoid messing up my nicely centred crankcase I simply removed the four jaw chuck with the work piece in situ. I then chucked up a bit of scrap in the three jaw and turned it to exactly 0.750" (19.05mm). No mistakes this time and I got it bang on.






I then replaced the four jaw and bored the crankcase for the cylinder. I managed to get a very nice tight fit on my hole gauge, and my digital calipers tell me it's exactly 0.750 











The next task to complete the major work on the crankcase was to bore the through hole for the main bearing and back plate to locate into. I don't have a height gauge at the moment (must get one of those but so expensive!), so I improvised and using the lathe bed as a surface plate and my digital callipers as a poor mans height gauge I marked out the centre.











Back in the four jaw, I used the tail stock centre as a guide to get the crank case close to centred on the punched point.






To fine adjust the position I used my shop made tool post wobbler. It appeared to be pretty much bang on with no movement after some adjustments.






Then I centre drilled, and used a succession of drills to take the hole size out to 12mm.
















Looks like I forgot to take a photo of the boring process again! I think it's because I found that part quite stressful. This is the first part I've done any boring on and I was taking very slow to ensure I didn't overshoot.

It still needs some cleaning up and some holes drilled and tapped, but here is the mostly finished crank case.











Here's where I own up - somewhere along the way I've screwed up and the through bore is off centre to the left by about 0.010". I'm not quite sure how it happened, but I guess the only reasonable explanation is that the rubber in my wobbler is too hard and I couldn't tell that the work piece was still fractionally off centre. 

Does the 0.010" off centre mean I need to scrap the part and start again? Or do people think I can get away with it?

I appreciate all the encouragement and advice you guys bring. If you see me doing something stupid, or if there's a better way to do something please let me know!

Next I'll either do the main bearing (front part), or the back plate. I don't suppose it matters which I do first.

Cheers,
James


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## barnesrickw (Nov 10, 2015)

I think the two bores not being on center by that much is not going to let the engine make a full revolution.  I think you are going to have to remake the part.  But, it will be easier this time.


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## edholly (Nov 10, 2015)

Roboguy,  just had a look at the drawings - 10 thou off centre will be ok in my opinion. You might have to relieve a tiny bit of the inner sidewall bottom of cylinder one side of crankcase for conrod clearance, but this is normal in most engines anyway.

Make sure you mark out front and back bolt holes off the tunnel not the crankcase sides - or better use those components as the template initially only drilling tapping size in them.

If you make two opposing sides 10 thou wider - the dreaded file will aesthetically fix the visual problem and no one will ever know !

Try my sharpened needle for marking out on a scrap and see how fine the scratch is and thereby how accurate you can get with it ....good luck - and welcome to the world of subtle changes .... Ed


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## Roboguy (Nov 11, 2015)

edholly said:


> Roboguy,  just had a look at the drawings - 10 thou off centre will be ok in my opinion. You might have to relieve a tiny bit of the inner sidewall bottom of cylinder one side of crankcase for conrod clearance, but this is normal in most engines anyway.
> 
> Make sure you mark out front and back bolt holes off the tunnel not the crankcase sides - or better use those components as the template initially only drilling tapping size in them.
> 
> ...


Hi Ed, 

I had already realised that drilling the crank case mounting holes was going to be a challenge without the ability to do coordinate drilling (no mill), so that was why I made the drilling jig as my first step. I've drilled the jig tapping size, so hopefully it should allow me to get everything to line up. 

I've been dwelling on how I ended up with the crank bore so far off centre and on the way to work this morning it dawned on me. I am using 1" stock, but of course I made an amateur mistake and forgot that 1" stock isn't exactly 1"! I measured it tonight and sure enough, it's 1.008, so there is the best part of my extra 10 thou. Basic error, and one I don't plan to make again! 

Started work on the main bearing tonight but haven't made much progress. 

Cheers, 
James


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## Roboguy (Nov 11, 2015)

barnesrickw said:


> I think the two bores not being on center by that much is not going to let the engine make a full revolution.  I think you are going to have to remake the part.  But, it will be easier this time.


Thanks for the feedback. I am going to forge ahead for now and see how things fit together once I've got the main parts made up. I've prepared another crank case blank, so if it's not looking good I'll remake it. 

Cheers, James


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## edholly (Nov 12, 2015)

Guys, 

Sorry James - just a bit off topic !

Check out this thread and look at the picture adjacent to the HMEM logo !!

http://www.homemodelenginemachinist.com/showthread.php?t=23458

1st photo after the youtube link ... !!!


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## Roboguy (Nov 12, 2015)

edholly said:


> Guys,
> 
> Sorry James - just a bit off topic !
> 
> ...


Nice work Ed! I've just read your thread and there's some interesting learnings in there. 

I just about finished the main bearing last night. Just have to drill and ream for the crank.


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## mattty (Nov 12, 2015)

Where can I find the plans for this engine.
Kind regards Matt


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## Roboguy (Nov 12, 2015)

mattty said:


> Where can I find the plans for this engine.
> Kind regards Matt



Hi Matt,

You can find the plans for the Boll Aero and several other engines on the Model Engine News website here http://modelenginenews.org/plans/

Cheers,
James


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## Roboguy (Nov 15, 2015)

Well I've managed to make some good progress over the last few evenings and now have the front bearing and back plate done (with the exception of the crank case screw holes).

I started with the main bearing. I cut a length of 1" square aluminium and faced it up, then marked out the centre, and the length to turn down at the front. Then I chucked it up in the four jaw and used the tail stock centre as a guide to get it roughly centred up.






I then turned it down to exact diameter and length and used a round nosed tool to produce the fillet in the corner between the mounting flange face and the bearing.






Back in the four jaw chuck with shim to protect the just turned surface, it was trued up and the spigot that will locate into the crankcase was turned with repeated testing for a very tight fit.
















Once the spigot was finished, the hole for the crank was drilled out to 7.7mm (0.303") ready for reaming with a 5/16 reamer.






And that is the main bearing completed with the exception of the holes for the crankcase screws.





















With the main bearing completed the next job was the backplate. I cut a length of 1.5" aluminium to length, plus enough for the cylinder head and a chucking allowance. I then chucked this up in the three jaw and faced the end and tidied up the outer diameter for a short length.






I then marked out the 0.400" to turn down for the spigot that will locate into the back of the crank case and proceeded to turn that down to 0.890", repeatedly test fitting with the crankcase as I got close to the final diameter.


























Happy with the fit I reversed the backplate, protected the turned spigot with some shim and rechucked it in the three jaw. I then faced it to length - exactly 0.150".






The next step I was a bit nervous about. It is a blind bore that leaves quite a thin wall so I didn't want to overshoot in any direction and push through. It's also the first time I had done a blind bore so there was that aspect to figure out as well.































Next up the cylinder I think...


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## quinette7 (Nov 15, 2015)

Roboguy -

You are making good progress.  I'm enjoying following along.

Bob


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## Roboguy (Nov 26, 2015)

I've made a bit of progress with the cylinder. I ended up making it from 1" square stock as that is the only size I had to hand of suitable material. Next week I plan to visit the metal suppliers and pick up some more stock for this and other projects. I had a piece of steel already cut which was a longer than necessary, but I decided to just go with it to avoid wastage.

I started by turning the required length down to the largest O.D. of 0.800". I then made a mistake, which if I had taken the time to think the machining sequence through more carefully would have been easily avoided. I turned the end of the piece down to 0.700" which is the O.D. of the top part of the cylinder. I should have turned the 0.750" for the bottom part so that I could test fit it in the crank case to ensure I got a tight fit. I ended up turning the 0.750 without being able to trial fit and as a result it is probably about 1 thou undersize, but it's not sloppy in the crankcase so I think it will be fine.

I then bored the cylinder 0.500" right through and parted it off. I then re-chucked it in the three jaw chuck and faced the bottom end to length.





















I'm now in the process of drilling the various ports and milling the transfer passages.

Couple of questions:
1. I've read about using lapping paste to lap the piston to the cylinder. Do people use diamond lapping paste for this and if so what grade / micron size?
2. What size prop should I be using with this engine?

Cheers!
James


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## edholly (Nov 26, 2015)

James,

The process I use that I was taught to me by David Owen and is in fact on his Owen Mate plans. For the cylinder you make a simple lap and use diamond paste to lap the inside of the bore.

The lap is machined to about a thou undersize then a blind hole is drilled and tapped one end. A hacksaw cut then divides it and a screw or grub screw wound into the tapped hole. Mount the lap in the lathe at a slowish speed and manually run the cylinder up and down with some fine paste on it. Make sure you cover your lathe and everything around it as the paste will work nicely on all the mechanical parts wearing them out super fast !  The deeper you go with the screw the more it expands to lap the inside of the bore to a fine finish and also the internal shape you need which is ever so fine a taper to the top. You are looking to have a 1 or 2 tenths of a thou taper at the top from the ports - to actually pinch the piston tight there, but not so tight at the bottom of the stroke.

I then - until recently - (I bought a internal bore gauge) used that lap to measure the internal diameter of the bore and to make the piston to that size. By expanding or contracting the screw you can get an extremely accurate feel as to the taper and size that way. Make sure you scrupulously clean the lap first though - I use carby cleaner. It is a good idea to buy a sonic cleaner - they aren't expensive and do a remarkable job of cleaning with degreaser as the fluid. 

I then make the piston exactly to the top of the bore size plus a zillionth - First  I make it about 1/2 a thou oversize then use a flat (a ruler works well) with some fine wet and dry to linish the piston down to a size. All pistons have an internal hole and I have found making a scrap piece of alloy rod that size and pushing the piston on has enough holding power to be able to do this. No superglue etc needed. When I get very close I then make the gudgeon pin holes which will put the piston slightly out of shape and again using the wet and dry against a flat linish the piston exact. Sometimes the gudgeon will force the piston a bit out of shape again so I install it through the scrap alloy mounting rod noting ever so carefully which way it went in and forever that is the way it goes in and out.

The aim is to have the piston so tight at the top of the stroke it squeaks - and most times it will only go 3/4 way up the bore when first assembled. A bit of oil and turning back and forth with a propeller usually beds it all together. Occasionally I have made it too tight and have to disassemble and linish the piston a bit more, better this than to have the piston too slack. It is truly amazing how tight a piston can be in the bore yet the engine will start and run beautifully - and the secret of a good diesel is good compression.

I know this sounds complicated - but really it isn't, and I can tell you it sure beats making several piston/cylinder combos in the hope that one will work !

Keep up the great work .... Ed


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## Roboguy (Nov 26, 2015)

Thanks very much for that detailed explanation Ed!

That certainly gives me a very good idea as to how to complete that critical step.

Novice question - how critical is the width of the transfer passages in these engines? Reason I ask is that I was just about to mill these and realised the plans call for a 5mm slot drill, and the smallest I have is 6mm. Do I need to hold off and order a smaller bit, or would a 6mm suffice?

Cheers,
James


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## edholly (Nov 27, 2015)

6mm v 5mm is a 20% increase which will slow the gas passage down a bit - but in imho I don't think it will matter one iota, the engine is not a fire breathing hodrod, where such things will affect performance.

In fact I've just looked at the plans again and the inlet holes determine the gas flow, so 5 v 6 mm will make zero difference.                  .....         Ed


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## Mechanicboy (Nov 28, 2015)

To check the piston/cylinder tolerance is correct: Dry piston/cylinder ---> The piston feel tight into the bottom of cylinder. Oiled piston/cylinder ---> The piston feel loose in bottom of cylinder and more and more tight on way to top of the cylinder. The cylinder/piston must be dull grey (a lot of oil pockets in surface) after lapping is done, also not mirror finished surface.

It is important the cylinder will expanding to "parallel cylinder" and keep compression under running. If the cylinder was parallel then the cylinder will expanding to loose compression and, the engine will stop when engine is up to working temperature.


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## Roboguy (Nov 29, 2015)

edholly said:


> 6mm v 5mm is a 20% increase which will slow the gas passage down a bit - but in imho I don't think it will matter one iota, the engine is not a fire breathing hodrod, where such things will affect performance.
> 
> In fact I've just looked at the plans again and the inlet holes determine the gas flow, so 5 v 6 mm will make zero difference.                  .....         Ed



Thanks for the reply Ed. I've taken a gamble and used the 6mm - I've also ordered a 2/3/5mm endmill pack of ebay today so I can always remake the cylinder if this one doesn't work out.

I've made some more progress this weekend but have run out of time to post an update tonight.


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## Roboguy (Nov 30, 2015)

The next step was to drill the various ports in the cylinder and mill the transfer passages. Because I don't have a mill yet I am doing all my milling operations in the lathe on the vertical slide. I used a dead centre in the headstock spindle to assist with lining up the end mill over the transfer port. 

Before the chorus of "you shouldn't be using chuck to hold a milling cutter" - I know. An ER32 collet chuck and set is on my Xmas wish list! 



























For a change I decided to start working on some of the fuel system parts next. The venturi is the obvious place to start. The plans suggested making this part from 5/16" square aluminium, but I didn't have any. So I turned down some aluminium round to 0.313" for 0.500", then 0.443" for 0.250", and finally back to 0.313" for the final 0.250". The 0.443" is the width across the diagonal of a 5/16" square bar, which left it the right diameter for me to then mill it square in the shop made dividing attachment that I got with my lathe. I then cut a 5/16-22 BSF thread instead of the 5/16-24 UNF thread specified as I don't have any UNF tap and die sets.


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## Cogsy (Nov 30, 2015)

Not using a chuck to hold a milling cutter relates to a Jacobs chuck (drill chuck) as they cannot withstand the size loads of milling and dangerous things can happen. Your lathe chuck should be more than up to the task of milling work I would think.


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## Roboguy (Dec 13, 2015)

Hi all,

I've not had much time to work on the engine over the last week or so - lots of end of year Christmas functions and family commitments!

I have made a little progress though. Firstly I machined up a couple of Jam nuts that fasten the venturi body to the crankcase. These I machined from some scrap round brass I had in my junk box. I turned them to diameter, drilled and tapped 1/4-22 TPI BSF as I have a good quality set of BSF taps. I then used my shop made dividing head to mill the hex nut flats, and finally parted the nuts off in the lathe. I forgot to take photos of the process, but here are the finished products.






After test fitting the venturi body in the hex nuts I felt the thread was a bit sloppy. I'd not set the split die far enough apart and had over-cut the thread on the venturi so I decided to remake it. Once done I drilled and tapped the crankcase, and also drilled the exhaust port in the crankcase while I was at it.






The next part I decided to tackle was the cylinder head. I faced up a suitable length of 1.5" aluminium in the three jaw and turned it to diameter. I then drilled and bored the 0.700" hole for the cylinder. I clearly need a bit more practice with the boring bar as I had it almost exactly to size with the cylinder just about fitting in. I probably needed to take 0.001" off, but managed to overshoot and now the hole is one or two thou to big. I'm going to remake the cylinder anyway as it is also a bit loose in the crankcase, and I now have a smaller end mill to mill the transfer ports the correct size.











I'm about ready to turn the fins now. I ground a HSS tool almost exactly to size. It's 0.145" wide, and the space between fins is supposed to be 0.150" according to the plan.






Slowly making progress...


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## Roboguy (Jan 6, 2016)

Christmas, summer camping holidays and other activities have slowed me down over the last few weeks, however I have finally managed to make some more progress on my engine.

Turning the fins with my specially ground tool worked reasonably well. The square end left a bit of chatter but I'm willing to live with it. This engine is definitely all a learning experience for me at this stage so getting a perfect finish on each part is just not realistic. So, after creating a small mountain of swarf on the lathe I had a pretty good looking cylinder head, and that's when I made my mistake. When parting off I didn't support the part, and it bounced back under the chuck which gave it a decent whack, gouging the bottom fin and bending it back upward toward the fin above.

Question: how do people normally support a part like this when parting off to ensure this sort of thing doesn't happen?





















After I got done wailing and gnashing my teeth for a bit, I straightened it the fin out and took a skim of the circumference of the whole cylinder head. The bottom fin is still not quite straight and has a great gouge in the bottom but I'm going to push on for now otherwise this engine will never run!

I had ordered some fasteners and some nice metric spiral taps before Christmas and they had arrived, so I decided it was time to drill and tap the crankcase. I used a drilling jig I had made earlier to first drill the main bearing and the backplate, then the plan was to drill through these to ensure the holes all lined up. That's when I made my second stupid mistake!

While drilling the *first* hole in the crankcase, I managed to break the 2.5mm drill bit I was using. I think I probably tried to go to fast and the bit caught on the edge of the existing hole in the main bearing part I was drilling through as it was biting into the crankcase material. The shear would have been enough to snap the small bit. 

Lot's of bad words ensued and I took a break for a day. 

Then I remade the crankcase, and this time managed to get a really nice fit for the cylinder, and then went straight into drilling and tapping again. This time round I spotted through the main bearing holes, then removed the part and drilled the crankcase holes on their own. I took it nice and slow, making sure to retract the bit and allow the swarf to clear every now and then. Probably not necessary considering I was only drilling 0.250" deep holes, but I really didn't want to be making a third crankcase! 

Spotting through the fins on the cylinder head had me holding my breath, but it all went well and I now have the crankcase all drilled and tapped. 











The image above also shows the finished tommy bar. The plans suggest 1/8" music wire, but I didn't haven any to hand so just turned down some 10mm diameter 1215 steel I have nearly 4 meters of.

Yesterday evening I made the compression screw. This was a pretty simple turning job apart from the thread. The plans call for a 1/4-32 UNF thread, but I don't have any UNF taps or dies, so I decided to make this a metric thread. I went with 6mm x 1.0 which is a slightly coarser thread (at approximately 25 TPI), but I figure that should be fine enough adjustment. The next challenge of course is cutting a metric thread on a older imperial lathe. My Myford Super 7 has a quick change gearbox, and by changing the final gear on the tumbler assembly to either a 33 or 34 tooth gear you can get very close approximations to most metric pitches (Harold Hall has a handy reference table here http://www.homews.co.uk/page346.html). So, using a 34 tooth final tumbler gear I cut my 6mm x 1.0 thread, and then finished it off with a die. All that remains to finish this part is to cross drill the compression screw and press in the tommy bar.






I'm debating with myself what to tackle next. I'm wavering between finishing off the last remaining parts for the fuel system, or moving on to the crankshaft...


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## 10K Pete (Jan 6, 2016)

I stick a pin/rod in the tail chuck and poke it into the piece. Or for little stuff
I just hold a hex key in there.

Pete


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## Cogsy (Jan 6, 2016)

For tiny stuff that tends to disappear on parting I normally place a rag under it just before parting. Of course I make sure I'm never touching the rag while the lathe is running.


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## petertha (Jan 6, 2016)

If I understand correct, both the chattering & sudden part might be related to the relatively wide parting tool plus it being a rectangular section. It might be better to try: 
- a thinner width blade 
- slight angle (viewed from top) so it parts through at a thin line vs. thick line
- with gummy aluminum, razor sharp stoned edge seems to work for me
- a dowel from the tailstock protruding into center of part to catch the work when parting occurs, keep your fingers out of there
- all the normal other parting tricks, centered tool, perpendicular blade, slower rpm/feed, cutting fluid...

Some thin walled stuff of certain alloys can just be a plain bugger. Sometimes I resort to partial parting & then finish the cut with a jeweler saw just to be safe. You would then need to finish the edge of course. Personally I try not to trust a parting tool for hitting the length in one shot at the best of times. Good luck


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## Roboguy (Jan 11, 2016)

Firstly thanks to Petertha, Cogsy and 10K Pete for your replies to my parting off question.

For the record, the parting off tool I am using is a standard Eclipse thin blade tool for Myford lathes. You can actually see it in the background in a couple of the photos below.

Over the past few days I have made some progress on the rest of the parts for the fuel system. I've just got to finish remaking the Venturi (for the third time!), as I need to make hole for the spray bar smaller. I ended up making the spray bar slightly smaller than the plans call far as I had to use a 6BA thread  as I didn't have taps and dies for either the 6-32 UNC the plan uses or the 3.5Mx0.6 metric alternative. 

Anyway, here's some progress pics. Hopefully the next lot will have the fuel system finished and in place on the crankcase, and I'll finally be ready to start work on the crankshaft.


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## 10K Pete (Jan 12, 2016)

Lookin' good! You have an audience here.

Pete


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## burkLane (Jan 12, 2016)

Following along and this build has inspired me to make this my first engine also!
Lane


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## Roboguy (Jan 13, 2016)

Hi guys,

I'm glad people are finding this interesting! I realise it's a pretty simple build compared with all the other masterpieces I am following on this forum at the moment, but everyone's gotta start somewhere right?!



burkLane said:


> Following along and this build has inspired me to make this my first engine also!
> Lane



Hey Lane, thanks for following - it's been pretty achievable even for a complete novice like me thus far. However I am about to start tackling the hard parts. As everyone has already pointed out the tough part will be getting the compression right with a good piston / cylinder fit.

Cheers,
James


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## Roboguy (Jan 14, 2016)

So I got a little time in the workshop last night and managed to finish of all the fuel system parts apart from the needle as I need to get some 1/16 music wire for that.

I milled the square section on the replacement venturi and then cross drilled 2.8mm for the correct fit from my slightly narrower spray bar. As per my earlier efforts I used the vertical slide and my shop made dividing attachment for the milling. 











While I had the dividing attachment set up I also milled a short length of brass I had previous turned down, drilled and tapped in order to make a 6BA nut for the spray bar. Here's the finished product.






Next job on the list was to cross drill the spray bar. This required drilling a 1mm hole through a 2.8mm brass tube. That's tricky given my experience level and the tools I have at my disposal. I've not had any luck drilling anything accurately with my budget drill press, so decided to do this on the lathe as well. This way I could accurately position the work piece. It worked out quite well as you can see.
















The final job for the night was going to be adding the counter sinks in the back plate. Boosted by my previous success drilling in the lathe I decided to continue with that approach. I should have heeded the warning voice in the back of my mind that said "that counter sink bit looks an awful lot like a milling cutter...". Naturally on the second hole the Morse taper gave up and the drill chuck spun loose. Luckily not too much damage was done, but one of the holes is a bit wobbly. I swapped the drill chuck out for the lathe chuck which solved the problem. I used a 3mm drill bit to centre the work piece before switching to the milling cutter. It worked well other than the fact that it has highlighted to me how knackered my old 3 jaw chuck is - the run out on that is awful!




































Next up I am going to tackle the crank shaft. The plans call for the crank to be made as three separate parts using a machine screw for the threaded section, and a crank pin made from drill rod. Instead I plan to make the crank as single one piece unit. I'm going to try cutting the M4x0.7 thread on the lathe, and turn the crank pin as an eccentric turn using the four jaw chuck.

Righto - it's off to the workshop I go!


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## Roboguy (Jan 14, 2016)

This morning I managed to get a couple of hours in the workshop and the first thing I wanted to do was check I could cut a M4x0.7 thread reliably. I'm using a bit of an approximation where the 24 tooth tumbler gear and the 36 TPI position on my gearbox works out to a pitch of about 0.69 which is not too bad. 

I turned some 10mm 1215 down to 4mm and then using a 60 degree single point HSS tool I had ground, I tested how well I could cut the thread. The first attempt was pretty shabby. I was reversing the gearbox to return to the beginning each time as you can't disengage the half nuts when cutting a non-native thread (i.e. metric on an imperial lead screw). Obviously there is enough backlash / slippage in the gear train / gearbox when changing direction that the pickup on the thread wasn't reliable and the result was a bit of a mess.

After giving it a little thought I decided to try switching the motor direction instead and run the lathe in reverse to get back to the start each time. This worked much better, although it is a bit laborious as I have to wait for the motor to completely spin down before changing direction. The finished thread is sharp and an off the shelf M4 nut threads on and off beautifully.

I now feel ready to start on the crank shaft. I've cut a 3" length of 1045 steel and am ready to go.


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## kettrinboy (Jan 15, 2016)

Great progress so far , been watching with interest , the only thing i would have done differently is to skim up the main block surfaces to be square and flat because as you found stock material is not to size , and frequently neither is it square or flat , which can cause problems with covers and bearing housings not seating and sealing properly , still hopefully this motor will run and you will know better on the next project.
regards Geoff


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## modelmotor (Jan 16, 2016)

Hallo,

I have followed your work the making from a Boll Aero 1.8 model diesel engine.I made several Boll model engines myself,but after following your thread as well i must really say perfect done man and very great craftmanship it all fits and it all works fantastic.My gratulations for such a nice made and well running model diesel motor.At the moment i just finished the Boll 49 8,02 cc model glow engine.I hope that it will start and run at least.

                                                   Lots of sucess with your great metal working hobby.

                                                                                                       modelmotor-Europe.


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## burkLane (Jan 18, 2016)

Great thread!
I enjoy reading and looking at each of your finished parts. This helps me make the same using completely different tools. Works out nice because your about 6 parts ahead of me. Currently working on compression screw and next is spray bar and thimble parts.  Also had to go back and add the counter sinks on back plate. Somehow I missed those when drawing model and adding those complicated the part considerably doing it with my tools. Didn't even notice until I was looking at your nice screws in place  oops! 3 steps back!
Anyway looking forward to your next update.


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## Roboguy (Jan 28, 2016)

Hi Lane,

Thanks for your post! I was feeling reasonably good about my progress and then I saw the pic of those three beautiful engines in your latest post and I got completely demoralised! 

The speed and repeatability of CNC is definitely impressive. I love the work you are doing and the way you are tweaking the design to make it your own. 

Cheers,
James


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## Roboguy (Jan 28, 2016)

I've made a bit of progress in the last week or so. The crankshaft is close to finished. The 1045 steel I am using is a pig to turn. The drive belts on my lathe are knackered and the steel is so tough that if I took more than about a 10 thou cut the belt would slip and the spindle would just stop. My replacement belts have arrived so once this engine is finished I'll disassemble the lathe headstock and replace them.

Originally I said I was going to make the crankshaft as a single piece instead of the three separate pieces specified in the plans. Unfortunately I didn't think through the machining sequence properly, and so I've ended up having to use a separate crank pin after all, although I haven't drilled the hole for this yet.



























At this stage I couldn't help myself and had to test fit it together to see what the engine would look like with a crankshaft installed.






Next part to make was the collet for the prop driver. This was a pretty simple turning job out of brass. I added a small lip on the backend to assist with removal if it becomes difficult to get off the crankshaft later.






With the collet made and without changing the topslide angle from the 10 degrees used to turn the taper on the collet I started work on the prop driver. I've turned up the body of the part. I now just need to turn the internal taper, part it off and add the knurl on the front face.






Hopefully I'll be able to finish these parts off this weekend and make a start on the con rod. 

Only a few parts remaining now but obviously I still have to tackle the the most difficult part being the piston (in terms of tolerence of fit at least).

Cheers,
James


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## burkLane (Jan 28, 2016)

Roboguy said:


> Hi Lane,
> 
> Thanks for your post! I was feeling reasonably good about my progress and then I saw the pic of those three beautiful engines in your latest post and I got completely demoralised!
> 
> ...


 
Thanks for kind words on my work.  Im a better photo guy then machinist 

Cnc tools have some very cool benefits and some very big drawbacks.
Not much room for errors in process, setup and tools. Only e-stop and by then tools and parts are destroyed. Time it takes to go from design to a part can vary from an hour to couple days. Much like you noted on the spray bar fab were valid and I spent days working out feeds - speeds- tool paths and model designs to make just 1 part with a 3-4 failures. 
  Then comes the cool benefit of repeat your successful setup / process and make a pile of good ones. Kind of the reason for making a couple complete assemblies. After all that effort why not make another in 1/10 the time.

I can safely say I have learned more in the last month building an engine or any design by someone else for that matter then in the previous year doing my own projects. It was easy for me to get in a rut of making my stuff with setups that are proven and not learn or challenge my skills and tools.
Also looking at threads like this to inspire me to take on the challenge.

You mentioned demoralized  "don't be" I want to inspire like you and others have done. I have no doubt this project is going to test my metal! Might need to work out a trade with you  or other builder on some parts best made on a lathe.  I don't know if I can make useful or functional crankshaft / piston / cylinder. Thinking this might be only way to get one running . 
Anyway great thread and always enjoy the updates and pictures.
Lane


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## Roboguy (Feb 4, 2016)

After drilling a  0.250" hole through the prop driver to I needed to cut the internal taper to mate to the brass collet I had previously made. The issue was that the 0.250" hole was going to be way too small for any of the boring bars I have, so I was pondering how best to grind a small boring tool from a piece of HSS. Digging through my odds and sods of HSS tool steel I came across a small hand ground boring tool I didn't even realise I had. It was in amongst the dozens of odd custom ground tools that came with the lathe when I purchased it. 






This worked perfectly and I was able to easily cut the internal taper to mate to the collet. The next challenge was that the plans called for the face of the prop driver to be knurled with a straight knurl. I only have one knurling tool with fixed wheels to cut a diamond knurl. With no other option, I mounted the knurling tool face on to the workpiece and plunged it into the part. The result actually turned our really well and looks just like the prop drivers I have on a couple of vintage diesels I have from years past.


























The next part I decided to tackle was the con rod. I had some 0.240" thick alloy plate which I needed to reduce to 0.160". With no mill I need to do any milling operations in the lathe, so I cut a section, mounted it in a vice attached the vertical slide and milled it to thickness.

With that done I cut a blank 0.340" wide, and mounted it in the four jaw chuck. I centre drilled the end and using a live centre in the tail stock for support, started turning the shaft.





















That's where I ran out of time last weekend. I'm off out to the workshop now to see if I can make some more progress on the con rod.

Cheers,
James


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## Roboguy (Mar 1, 2016)

Wow - it's been a while since I've had time to update this thread. Lot's of family commitments have meant I've not had much time in the workshop over the last few weeks. I have had a couple of failed attempts at producing the conrod though...

My first approach which I had started on in the previous post was to turn a section of flat aluminium and then mill the radius' on either end. At first this looked like it was going to work out reasonably well. I had turned the centre of the rod and drilled and reamed the pin holes and was reasonably happy with the result.






I had then planned to emulate an approach I'd seen on another website where a clever chap had built a modified version of the Boll Aero which he has called the Nelson 2cc. At the bottom of that page is a picture what I thought was a rather clever approach to turning the conrod. The next sequence of photos show my attempt to replicate that approach.


























As the last couple of photos show, my result was less than ideal. My setup clearly had way to much flex and play in it and the conrod bounced about during milling. It felt a bit dodgy, and eventually the mill bit and twisted the conrod and gouged the shaft. 

I wasn't feeling to optimistic about this approach so decided to try an new tactic. I had seen an alternative way of making conrods as described by Ramon Wilson in his 5cc Super Tigre build. 

This time I started with a length of aluminium bar and used a radius tool I had made from some scrap flat steel I had to hand. The radius tool turned a reasonably decent looking ball. I then turned the shaft and parted the work piece off with enough material left to turn the ball at the other end. Next I drilled a hole through the centre of another short piece of alloy rod the same diameter as the conrod shaft. I sawed the alloy rod with the hole length wise, then used this to clamp the shaft of the conrod and hold it in the 3 jaw so I could turn the ball at the remaining end. Unfortunately as the final picture shows stress of turning with the radius tool snapped the shaft of the conrod.


























I feel like this approach has merit. There are a couple of things I plan to try next. I will turn the blank to close to finished diameter before any other operations. This will dramatically reduce the amount of material the radius tool needs too remove and therefore the amount of sideways stress placed on the conrod in the final operation. Secondly, I plan to rework the radius tool slightly to remove the width on each side of the radius. The profile is far to square on either side of the half circle. If these were sharper shapes, they would cut more easily and reduce the side loading on the work piece.

Unfortunately it's going to be a few more days before I can get the time to try all this, but having some time to think about it may unlock some more ideas.

I always expected the conrod, piston / contra piston and lapping to be the most difficult aspects of the engine. 

Of course if I had a mill and a rotary table this would be so simple... but where's the fun in that


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## edholly (Mar 2, 2016)

Without a mill you do have some difficulties

Maybe an approach you might consider is to bore the big end and little ends to size in a piece of suitable diameter rod with some overhang each end, then machine the central part of the rod using the chuck one end and a live/dead centre the other end. Small cuts so as not to overload the weakened end where the hole is. Then use the dreaded hacksaw and linisher/grinder to get the rounded shape of the ends of the conrod. I am not too ashamed to say I have done this many times .... Ed


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## quinette7 (Mar 4, 2016)

Roboguy -

The "MLA Diesel" uses a connecting rod that has some similarities with the one you are making.  I built my "MLA Diesel" with the help of a milling machine and rotary table, but the instructions that came with the kit tell how to make everything on a lathe.  I sent an email to Andy Lofquist, who designed the "MLA Diesel" and markets the kits, asking for permission to post his copyrighted text, drawings, and photo of his approach for making this part, for your possible benefit.  He graciously agreed.  I have no ties with Andy, but I feel it is appropriate to thank him for his assistance by posting his website of lathe accessories and Diesel kits here.
http://www.statecollegecentral.com/metallathe/





[/URL]





















I hope this gives you some more ideas on how to proceed.

Bob


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## joco-nz (Mar 5, 2016)

The method Bob documents reads well.   I did some snooping and youtube spat out [ame="https://www.youtube.com/watch?v=4kVnTZ3eaVw"]this approach[/ame].  While its done using a mill I would think it could be adapted to a lathe with vertical slide.  This guy gets his fingers a bit close to "high speed spinning things" for my comfort levels. However I would think the use of needle-nose pliers or some other tool could be used to get fingers out of the way.  Anyway it is another approach to consider.

Cheers,
James.


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## Roboguy (Mar 6, 2016)

Thanks for all the replies guys. It certainly helps with the motivation to post if you know that someone out there is reading your rambles!

Who knew there were so many challenges and so many solutions for making what seems like a very simple part. Those replies have all taught me something more. I intend to have another crack at my last method although I will improve my radius tool as per my last post before trying. I also intend to try some slightly different alloy bar which I think will have a higher tensile strength and is probably better material for the conrod anyway. 

I had always intended to mill the faces of the rod ends using exactly the approach illustrated at the end of Bob's post, so it's encouraging to see that I am following a tried and true approach there.

If my next attempt doesn't work out then I'll probably do as Ed suggested and fall back to a file to get the radius on the ends.

Will keep you posted!

Cheers,
James


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## Roboguy (Jun 14, 2016)

Hi all, I haven't given up or fallen of the face of the earth. I've been super busy with work family etc and haven't had much time out in the workshop for the last couple of months. After about four failed attempts at making the con-rod I probably needed a wee break anyway to recharge my enthusiasm.

I decided to go low tech with my last attempt to make the con-rod and although the result is not perfect, I think it will be good enough for my needs for this engine.

I started out with some alloy rod which I turned down to 0.300". This was a mistake which you will see later, but hopefully won't effect the overall functionality of the finished part. I then turned the centre section of the rod to 0.156" for the correct length. Having something that now looked like an odd shaped bar bell I needed to mill flat both ends of part.











Next I drilled and reamed the gudgeon and crank pin holes at each end. With that done I was back to forming the dreaded radius on the ends. This time I turned up some 1215 steel filling buttons and sandwiched one end of the rod between them.






I then carefully filed the radius using the filling buttons as a guide.











Here you can see the results of my earlier mistake in turning the rod to 0.300" along the length at the start. Each side of the radius on both ends of the rod has a second radius along the same axis as the rod. I don't think this will be enough to materially affect the strength though, and as I've said before this engine isn't likely to see a whole lot of running so I'm going to forge ahead and hope this con-rod holds out.

So, almost there. Last major steps are to lap the cylinder, and turn the piston and contra-piston and lap those to the cylinder.

To that end the next thing I plan to make is a lap for the cylinder. I plan to replicate one like this.






You can see more about how the lap works in the build thread here http://modelengineeringwebsite.com/Super_Tigre_6.html

Question - if my cylinder is 1.402" long, would I be correct in assuming my lap needs to be a little bit longer than that? I am guessing that using a shorter lap than the length of the cylinder would be a bad idea as it would be difficult to get a consistent finish along the whole length, or is this fine as long as you move the cylinder up and down the lap as you are lapping?

Cheers!
James


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## AlbertdeWitte (Jun 15, 2016)

Great built!

I like your milling technique in the lathe!


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## Roboguy (Jun 25, 2016)

Over the last week I've managed to get a couple of nights out in the workshop to make the lap for lapping the cylinder. I decided to try my hand at drawing it up in CAD first. I've never really done any CAD before and so thought it about time I learn the basics. I used FreeCAD which seems a little rough round the edges but appears to be being actively developed. If anyone has any suggestions for good (preferably cheap or low cost) CAD packages please let me know. 

I've learnt a bit with my lap design already. The thin end of the taper on the mandrel is just to narrow meaning I had to use a very very thin boring bar. I actually ended up making one from an old HSS drill bit as I didn't have anything suitable, but it simply had too much spring in it and it was very difficult to get the internal taper to match the taper on the mandrel.

Here's the lap components and then the assembled lap.











I then mounted the lap in the 3 jaw chuck and turned the lap to size. A final test fit with the cylinder has it pretty much bang on and ready to go.











Tomorrow  I plan to try my hand at lapping!


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## petertha (Jun 25, 2016)

Looks great. I remember seeing that lap design in the Super Tigre link. One thing maybe you can explain I never quite understood. The removable segment closer to the chuck [1] I assume is to allow the sleeve to extend over the lap length. But why does this [blue segment] have to be removable & bored to same mandrel taper? Couldn't you just turn that portion down from the same stock, reduce as necessary to accommodate bore ID & start the tapered portion from the end to suit the lap segment? Hopefully this question makes sense. Attaching sketch. 

Also if its not too late, it would be interesting to measure your lap barrel before/after lapping to see what amount gets consumed during the operation.


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## Mechanicboy (Jun 26, 2016)

Roboguy said:


> Question - if my cylinder is 1.402" long, would I be correct in assuming my lap needs to be a little bit longer than that? I am guessing that using a shorter lap than the length of the cylinder would be a bad idea as it would be difficult to get a consistent finish along the whole length, or is this fine as long as you move the cylinder up and down the lap as you are lapping?
> 
> Cheers!
> James



Length of lapping tool for cylinder must be 3-4 times longer than length of cylinder to preventing "bell" formed cylinder.

Lets take a look at a typical lapping job - that of producing a fine finished bore and piston for an IC engine. In fact, piston and bore are both lapped in separate operations (NOT both together). All of these operations will be carried out in the lathe (and I need hardly mention the importance of keeping lapping compounds off the machine, particularly the chuck and slideways). For the bore an expanding lap is ideal, and this should be some 3-4 times the total length of the bore. The first grade of abrasive would be mixed with light machine oil (10W or lighter) and liberally coated on the inside of the workpiece. Similarly, the slurry would be added to the outside (and inside assuming it is of the ventilated type) of the lap. The lathe would be started at about 300rpm (for a nominal 1" bore) and the lap passed rapidly through the bore, keeping it moving back and forth without it coming out the bore. How to hold the lap? well, perhaps the best way is with a 'floating' tailstock holder, and failing this holding with the hand is a method as good as any. Be careful when holding the lap by hand as it's possible it may jam, hold it lightly and expect the unexpected. Remember also that unless the lap is maintained dead parallel with the bore (an almost impossible task) it will tend to bell-mouth the bore a little - hence the reason for making the work a little longer than finished size and trimming to length later. When the inside of the bore has achieved an all-over grey appearance, with the fine scratches appearing even and criss-crossing both ways, and with no evidence of any deeper scratches (as might be left by the reamer) it's time to move onto the next finer grade. The work will have to be removed from the chuck to clean it properly, and this should be done with clean paraffin oil followed by hot soapy water. The same procedure applies to the lap and all traces of the abrasive must be removed. The process continues until you reach the 'flour' grade of abrasive by which time the finish on the workpiece should be very fine indeed. A final polished finish, should this be deemed necessary, can be achieved using metal polish (diluted Autosol, or some liquid chrome cleaner). The lap should be a separate 'finishing' lap so there is no chance of contamination with the coarser grades of abrasive which might be embedded in the main lap. The piston is treated in a similar way except of course the lap is female. Work will continue with the coarse abrasive until (using the un-trimmed bore as a gauge) the piston will not *quite* enter the bore. At this stage finer grade abrasives are used and work continues until the piston will just enter the bore tightly. At this stage, it is usual to finish mating the two parts by using metal polish and briefly using the piston to lap the bore directly. Great care needs be taken but this method ensures that the fit is good for the entire length of the bore. 

To check fit is correct: dry piston/cylinder --> piston goes tight into cylinder. Oiled piston/cylinder --> piston is loose in bottom of cylinder and tight in top of cylinder. Also cylinder is tapered to make good compression and easy to start engine. Parallel cylinder will loose compression very soon under working temperature. The tapered cylinder will expanding under working temperature to parallel cylinder without loose compression.


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## Roboguy (Jun 26, 2016)

petertha said:


> The removable segment closer to the chuck [1] I assume is to allow the sleeve to extend over the lap length. But why does this [blue segment] have to be removable & bored to same mandrel taper? Couldn't you just turn that portion down from the same stock, reduce as necessary to accommodate bore ID & start the tapered portion from the end to suit the lap segment? Hopefully this question makes sense. Attaching sketch.



Hi Petertha,

The removable section you have highlighted in blue is used to knock the lap sleeve back of the mandrel if you want to loosen the lap (or replace the sleeve). If you have over expanded the lap you can just back off the screw and loosen the chuck and tap the screw which will cause the sliding section to push the lap sleeve back down the mandrel taper. Apologies for the clumsy explanation, hopefully the attached plan will help clarify things

The mandrel isn't actually tapered all the way up, pretty much as far as your green dashed lines go, then it is parallel. The sliding section is just a loose fit over the parallel part of the mandrel.

Here is my plan - apologies for all the drawing rules I've broken - I'm just finding my way here!








petertha said:


> Also if its not too late, it would be interesting to measure your lap barrel before/after lapping to see what amount gets consumed during the operation.



I measured the lap sleeve, but of course as you expand the lap during lapping the sleeve gets bigger. I should have measured the inside of the cylinder bore but didn't think of that until after I'd done the lapping.


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## Roboguy (Jun 26, 2016)

Mechanicboy said:


> Length of lapping tool for cylinder must be 3-4 times longer than length of cylinder to preventing "bell" formed cylinder.



Hi Jens,

Thanks so much for your detailed reply! Unfortunately I'd already done the lapping by the time I saw this so I may have a bell in my cylinder. Oh well, it's all a learning experience so I'll see how this one goes and if it doesn't work out I can always make another one!

Cheers,
James


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## Roboguy (Jun 26, 2016)

Well, my first attempt a lapping is done. I'm pretty sure this is a long way from perfect, but this whole engine is just a skills development / learning experience so if I can get it to start and the end that will be a win!

Lap after lapping





Inside of the cylinder bore now looks pretty good.





In this photo you can still see some very slight scratch marks. To be honest the photo looks worse than reality. 





Next step will be turning up the piston and contra piston.


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## Mechanicboy (Jun 26, 2016)

Roboguy said:


> Hi Jens,
> 
> Thanks so much for your detailed reply! Unfortunately I'd already done the lapping by the time I saw this so I may have a bell in my cylinder. Oh well, it's all a learning experience so I'll see how this one goes and if it doesn't work out I can always make another one!
> 
> ...





No problem to relap with a longer lapping tool, it must be same resistand in all ways in whole length of cylinder under lapping. Never stay in same place under lapping, move in both ways while you are lapping the cylinder ---> you are creating cross hatching wall in cylinder. Wash and check, there is not tool marks and dull gray. Also it's very bad idea to lap the cylinder/piston to a mirror finish. Do it same with contrapiston but with tight fit into cylinder, still movable with compression screw/by pressure of compression.


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## goyeng (Jul 21, 2016)

roboguy..please reply my private message


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## gus (Jul 21, 2016)

Mechanicboy said:


> No problem to relap with a longer lapping tool, it must be same resistand in all ways in whole length of cylinder under lapping. Never stay in same place under lapping, move in both ways while you are lapping the cylinder ---> you are creating cross hatching wall in cylinder. Wash and check, there is not tool marks and dull gray. Also it's very bad idea to lap the cylinder/piston to a mirror finish. Do it same with contrapiston but with tight fit into cylinder, still movable with compression screw/by pressure of compression.




Hi Jens,

I have same engine half done 10 years ago. No lapping experience. No height gage to mark cylinder ports. Will be following this thread. 2 stroke engines are not easy to build and run. Thanks for the tips.


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## goyeng (Jul 25, 2016)

Some one please give me, your blacbarry id..
to give me tutorial build ball aero


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## Roboguy (Oct 31, 2016)

Hi guys,

So I got close to finishing and then life got in the way! Work has been absolutely manic, I'm in the midst of a bunch of home renovations, and my third child arrived safely a couple of weeks ago, so there hasn't been too much spare time to get out to the workshop!

I did manage an hour here and there over the last few months, but all I managed to do was destroy several parts I had already finished :wall:

I ordered a ER32 collet chuck and collet set from RDG tools in the UK and after a bit of fiddling got it mounted up to the lathe with about 0.0005" run out which I thought was pretty decent. 







I had previously made a piston lap which I planned to use once I had the collet chuck. 






I was a bit reckless with my piston at one point and in my haste I broke the skirt. After a string of bad words and a couple of days of brooding I remade the piston and got to lapping.





















The last photo above is just to show how I held the piston lap by hand while lapping the piston. I ran the lathe at 290rpm and used ~400 grit and then ~800 grit diamond paste to lap the piston. I know people have reservations about the use of diamond paste vs a silicon compound, but I couldn't find the later in NZ and as this engine will likely only run a few times and won't see extended use I figured I would make do.

I'd obviously left way too much extra on the piston and ended up taking nearly 4 thou off by lapping (which took forever!) before the piston just started into the cylinder.











That's about as far as the piston will go at the moment, and I am just about finished making a T-handled tool to use to lap the piston to the cylinder to finish the process. I'm following the process described at the bottom of this page http://modelengineeringwebsite.com/Super_Tigre_12.html

I also managed to stuff up my spray bar and needle thimble when I tried to solder the needle into the thimble. I had a bit too much clearance in the hole in thimble in my first version and the flux and solder flowed down the needle and very effectively soldered the thimble and spray bar together. :wall:

Lesson learned! I remade the parts and this time made sure the hole in the thimble was a tight slip fit for the 1/16" brass rod I was using for the needle (I was supposed to use piano wire but it was hard to come by and I had the brass rod to hand). 






One other little job I had to do was loctite and press the crank pin into the crank.






I've also made and lapped the contra-piston, although it appears I didn't take any photos of that.

So, all that remains now is to finish lapping the piston to the cylinder, and test fit and assemble the engine and I should be close to attempting a first run!

Cheers,
James Fitzsimons


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## bruedney (Oct 31, 2016)

Woohoo - workshop time - Looking good James

See you Wednesday

Cheers
Bruce


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## joco-nz (Oct 31, 2016)

roboguy said:


> ... And my third child arrived safely a couple of weeks ago...



congratulations!
th_wav


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## bruedney (Oct 31, 2016)

Roboguy said:


> and my third child arrived safely a couple of weeks ago,



Got so caught up in the engineering that I totally missed this statement

WOOHOO :thumbup:

Congrats James and Mrs James


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## Roboguy (Dec 29, 2016)

So, over the last month or so I've managed to grab an hour here and there and get the engine to a completed state. Here are some pics of the final parts collection and the assembled engine.

The last remaining job before assembly was to finish lapping the piston to the cylinder. I did this by making a t-handle tool and carefully lapping the piston into the cylinder with a very small amount of fine grade lapping paste.






Part way there:










All the way in:





Then it was time for a clean up and some family shots before final assembly:











Testing fitting some parts:





Today I finally had some time to finish assembly and try a start. After putting it all together I lashed up a crude test platform using an old saw horse:











Righto - time for the magic!

...

Bugger! It doesn't run. :wall:

My worst fears have been realised. I don't think it has enough compression and it appears to be leaking past the contra piston as I can see spent fuel and small bubbles around the base of the compression screw. Here is a (pretty rough) video of some attempts to start. It was difficult taking the video with one hand and attempting to start it with the other!

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


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## Roboguy (Dec 30, 2016)

Bit more detail on what I've tried so far:

- tightened all the screws holding the block, main bearing and back plate up snug
- made a paper gasket for the back plate as felt that it was leaking too much
- screwed the compression screw all the way down to see if I could get a seal but no luck

Been thinking about what next.

I think I'm going to try making a new contra piston and making sure it's really tight in the top of the cylinder. Hopefully that might solve the leaking out the top of the cylinder. The other joints seem to be ok now as there is no fuel leaking out anymore. 

I'm still keen to try and get a runner out of this engine, but I'm not about to remake a bunch of parts for the umpteenth time. I think if the contra piston doesn't get it running I'll probably be chalking this one up to experience and moving on.

I've realised now that this was not a great first project - take note any budding model engine machinists - small diesels are not a best first project!


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## bruedney (Dec 30, 2016)

Hi James

What about making a starting mandrel for a battery drill it might run once it has been spun a bit quicker

Cheers

Bruce


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## edholly (Dec 30, 2016)

Roboguy,

Don't give up - I am sure I heard a few pops when you were flicking... if that was the case then you should be able to get it to run.

The first start of a new motor is always the most difficult, settings unknown and piston / contra / cylinder fit unhappy as no running to bed it in even slightly.

I would try this .... 

With around 40% ether content say a mix 40 / 30 / 30 ether kero caster oil turn the engine on its side about 45 degrees so you can get raw fuel into the crankcase by priming with the fuel bottle, 3-5 drops maybe more, then a good prime into the exhaust. Turn it over without flicking about 5 -6 times holding the prop but with the contra backed off. Now with the needle valve a bit more than what you think is running position, start flicking as hard as you can. 

What you are doing is using the fuel as a means of just not making the engine run, but also the extra fuel will help seal anything that isn't fitting too well in its present state.

Be careful not to get a compression lock, although finger flicking shouldn't hurt anything, an electric starter can however.

Don't give up, when you are flicking using this procedure each 2nd or 3rd flick just turn the compression screw down a bit more, eventually you will feel it wanting to stop before tdc as the mixture fires, when this happens just leave the comp screw where it is or back it off by about 10 to 15 degrees only. If that wanting to stop goes away, keep the comp screw going down. Be careful not to get it so far down that it contacts the piston though.

When it starts you will need to be fairly quick to up the comp screw as the extra fuel helping seal everything burns off. 

Believe me we have all been where you are presently, and when it does get going it is a terrific thrill.

GOOD LUCK .... Ed


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## Roboguy (Dec 31, 2016)

Thanks for the encouragement Ed!

I'm going to remake the contra piston today and see if I can't get a much tighter fit. I feel like that is probably the main contributing factor to the lack of compression. Once I have that done I will follow your steps to attempt the start.

Unfortunately I don't have control over the ether content of the fuel I am using. It is an older bottle of commercial fuel, and even worse some of the ether has probably evaporated with age. To make things even more difficult you can't purchase model diesel engine fuel in NZ anymore, and you also can't buy ether as it is now a controlled substance (thanks to nefarious types who use it to manufacture illicit substances!).

Right - off to make a new contra piston - will report back soon.

Cheers,
James


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## bruedney (Dec 31, 2016)

Hi James

CRC Engine Start is a mix of petrol and ether etc. I wonder if you hold the can upside down (like a paint can) you would express all the propellant out and then be able to puncture the can to get the fuel out.

Is the ether more there for starting or is it there to aid running as well?

Cheers

Bruce


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## /// (Jan 1, 2017)

Hi James,
Are there any hobby shops in NZ that stock 'Hot Stuff' branded fuels by Ozzie Traders? If so, they may be able to get you the Ozzie Traders diesel.
Alternatively you could contact Ozzie Traders to ask if they have supplied anyone in NZ.
Apparently another option is visiting any Control Line Aero clubs as these guys still prefer CI engines.(this will be my first option when I get my CI built)
Regarding 'canned' starter mixes as sources of ether, from what I have researched, only John Deere brand is worth the trouble as it is 80% ether and apparently the remainder is mostly propellant, whereas the other brands are typically only 20-30% ether.

http://www.ozzietraders.com/Hot_Stuff_Fuel/Aircraft_Fuel/aircraft_fuel.html


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## Roboguy (Jan 1, 2017)

Hi guys. 

Thanks for the ideas re fuel. I had read about people trying to make their own from starter fluid. Perhaps that might be worth a try to boost the ether content in the fuel I already have. 

I made a new contra piston today and got a really tight fit. It's no longer leaking past the contra, but still no closer to starting. If anything it feels less like popping today. I can hear leaking past the piston under compression when I turn the prop slowly. It looks like the piston is a fraction loose now. I don't think I can face making another one though! 

Cheers 
James


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## edholly (Jan 2, 2017)

Roboguy, Don't discard the piston yet - if you are convinced it is too small there is a way of redeeming it called cherry bombing. 

BUT if you are getting popping then it wants to run, maybe the John Deere extra ether if you can get it will help - if you don't have enough ether you won't get a start. You really need a minimum of 33% but 40 is better. Leakage at the piston/cylinder interface is common especially on unrun engines - they need to run to bed in.

Re the saving of a piston ... 

I have used this process maybe 20 times now and it mostly works. I used it on my own pistons when I have made one a tad small, and on many worn out diesels bought on Ebay etc.

What you have to do is heat the piston on its own to a cherry red then drop it in oil. I usually go for a bit less than cherry and remeasure. Usually at this stage nothing happens I've even seen it regress slightly. If it grows great, if not - next time take it just a tad hotter and always drop in oil. 95% of the time it will grow, by the sound of things you are very close so you would be aiming for a 1 thou growth but I have seen them go 3 thou. 

I then make a simple push on mandrel and push the piston onto that then using a fine emery backed by a ruler, linish it down to the size you want on the lathe. Be careful this process removes metal when you are talking tenths of a thou pretty quick, also have a good speed on the lathe to try to keep the piston round, I use 770 rpm at least. You are aiming to get it into the bottom of the bore up to the exhaust by hand, but no further. It isn't till you assemble it that you work it back and forth to bed it in with some oil that you will get it to go over the top, sometimes takes a couple of minutes just a little bit more up the bore each back and forth movement, not too much pressure though as you don't want to make the conrod ends oval, so plenty of oil here too. If you feel it isn't going to get there then disassemble and take off another 1/10th thou.

BollAero's are great little motors - you will get it to go, just have to learn the tricks .... I think I remade both the piston and liner twice before I got it to run - that was about 3 years and 15 motors ago !


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## bollaero (Jan 11, 2018)

I do not look very often at this website, have only just read this thread.
People worry too much about things like the accuracy of marking out screw holes, Just a rule and felt tip pen for marking fluid and a scriber is ok provided you always do the one part first and spot drill through to the mating piece, you do not need interchangeability like on a mass production engine.
The easy way to make conrods is to use square bar, Drill the 2 holes then chuck one end and support the other, and turn the round centre section, also start to shape the big and little ends in the lathe. Then mill the ends down to required size, finally cut off excess length and file to shape. Never had one fail yet and have made a 7.5cc diesel using this method. BollAero 750 on youtube.


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## veedub (Feb 16, 2018)

I have read this thread over the last couple of days but alas, no photos.  Perhaps the photo hosting service is off the air.
Is there any chance these photos/videos can be resurrected and republished?
I too have built most of the Boll Aero but am totally hung up on the piston/liner fit.  My original cast iron contra piston actually had air going through it as the metal was so porous.
Perhaps the moderator can assist with recovery of the photos.
Cheers Peter


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## Herbiev (Feb 16, 2018)

Veedub, the problem with the photos is extortion by Photobucket. The owner has to pay around $400 to retrieve their pics or lose them.


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## veedub (Feb 16, 2018)

Sounds like extortion. Would the original Roboguy still have them on his phone or camera?  I need all the help I can get in my attempts to complete this project.


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## Pigi_102 (Feb 17, 2018)

There is another option.
If you use chrome there is an extension called Photobucket Embedded Image Fix that can be freely installed from chrome extension menu, that make the photo appears.
The problem is not that the author have to pay but that the viewer have to pay. 
Using this extension you can avoid the problem. 
Not sure if it is legal, but is in the chrome store, so it should not be our problem, eventually 

Hope this helps ( until it works ) 

Pigi


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## pengxing10 (Feb 17, 2018)

Pigi_102,Thanks for the tips so that I can see the photo


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## bollaero (Feb 18, 2018)

One way to help starting with a slightly poor piston fit is to inject a drop of  thin oil into the exhaust port, which helps the seal.
It will not work miracles, but helps in marginal cases.
I have kept diesel fuel for several years in metal cans a nd found it still works ok.

Do not give up, it is not unusual to have to make more than one piston on a first engine, it gets easier with practice, and  bigger engines are not so tricky as small ones, hence my idea to design a larger engine  based on the idea of  the ML Midge .

I am now up to a 7.5cc engine which turns a 12x6 prop happily and ran first time, l still had to adjust the contra piston fit a bit by whacking a brass spinner nut into the top of it to expand it slightly so it did not run back when running.


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## veedub (Feb 20, 2018)

Thanks for the assist with Chrome and the Photobucket extension.  Works very well!

Well it did up to page 6 or so and then it would not let me copy the photos which are the most informative part.


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## Stieglitz (Feb 21, 2018)

Hi Roboguy, Would love to see your photos,seems photobucket needs to be unlocked.
Will keep track on your progress,will inspire me to take the leap.
Cheers
Allen.


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## Roboguy (Feb 22, 2018)

Hi all,

Neat to see some interest - it looks like photobucket have gone a bit nuts. I don't have time to move all the photos to a new hosting site and repost the links here at the moment, but I think if you visit my album on the photobucket site directly you should be able to see the images.

http://s604.photobucket.com/user/wlgjafi/library/Boll Aero build?sort=3&page=8

If that doesn't work and anyone desperately wants to see them PM me and I'll figure something out.

Unfortunately I haven't had much time to spend out in the workshop for the last 12 months or so. I just can't get diesel fuel or the ether to make any locally, so I intend to try replacing the diesel head with a glow plug head to see if I can get this engine running. If and when that happens I definitely post some updates!

Cheers,
James


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## ixb1 (Feb 22, 2018)

Hi Roboguy
For sharing photos i like Pixhost. Its reliable,no missing links.
I was problems with buying ether too.This was reason why i start making glow engines only.


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## Stieglitz (Feb 23, 2018)

Hi Roboguy,Checked out the photos via your link,thanks for that, Like what your doing And will follow your progress with interest.
Love the Super 7 I have restored one myself over a period of time and will be putting it to good use.
Cheers
Allen.


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## veedub (Feb 23, 2018)

Hi ixb1,  what engine are you holding in your photo?  Did you build it and are plans available?


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## ixb1 (Feb 24, 2018)

veedub said:


> Hi ixb1,  what engine are you holding in your photo?  Did you build it and are plans available?


This is my latest finished baby MP3.2 which i designed some time ago.You may look at "finished projects".


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## joco-nz (Feb 25, 2018)

Roboguy said:


> ... I just can't get diesel fuel or the ether to make any locally, so I intend to try replacing the diesel head with a glow plug head ...



Yeah the collateral damage in NZ due to certain illegal drugs is ether is now a controlled substance. So unless someone has some bright ideas, from what I can tell the model "diesel" engines using ether based fuel are a dead duck in NZ.

Such a pity.

Looks like IC's ignition is going to have to be glow plug, Hot Bulb, true Diesel or Spark.  Of course if someone has some cunning plan on the ether front I would love to know about it as I am sure would James.

Cheers,
J.


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## Stieglitz (Feb 25, 2018)

Hi joco-nz, On the subject of etherless fuels I follow an Oz Model Aero Engineer (he writes for several magazines goes by the name of Brian Winch)that has done a fair bit of testing on model compression ignition engines.
Very interesting findings,he also has tested the different oils that are blended in the fuel.
Try his E-Mail : [email protected]
Cheers
Allen.


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## Stieglitz (Feb 25, 2018)

Hi joco-nz, On the subject of etherless fuels I follow an Oz Model Aero Engineer (he writes for several magazines goes by the name of Brian Winch)that has done a fair bit of testing on model compression ignition engines.
Very interesting findings,he also has tested the different oils that are blended in the fuel.
Try his E-Mail : [email protected]
Cheers
Allen.


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## Stieglitz (Feb 26, 2018)

Hi joco-nz, There is a a guy here in OZ a model engineer that has been doing research into etherless diesel fuel,has come up with some interesting findings.He proof runs the fuel mixes through a common test engine the results look promising.
He writes articles in many aeromodelling magazines.
Cheers
Allen


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