Author Topic: Boll Aero  (Read 2492 times)

Offline Pete49

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Boll Aero
« on: September 12, 2014, 06:59:20 AM »
hello chaps and chapesses I am attempting to build the Ron Chernich Boll Aero engine and have a couple questions.
1/ contra piston..... what is it for and does it float?
2/ stressproof steel ( for crankshaft) what the devil is it??? They suggest 7/8th HT bolt as a option but not sure if it is easy to turn.
I'm sure I have more to ask but these are the main ones for now  :old:
Pete
I used to have a friend.....but the rope broke and he ran away :(

Offline Jasonb

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Re: Boll Aero
« Reply #1 on: September 12, 2014, 07:40:02 AM »
The contra piston does "float" but should be a very firm fit, you don't want it slack. By turning the screw in the top of the head the contra piston is pushed down, the action of the engine firing will push it up against the screw and it adjusts the compression ratio.

EN24T (817M40T) would be a suitable UK steel though on something this small if its just for display then EN8 (080M40) should do. The option of using a bolt is also OK as its not a big crank. All these are higher tensile steels than your usual EN1A mild steel.

If you have not done so take a look through some of Ramon's Diesel build threads, you will see him using bolts on some of those and also the critical lapping to get teh right piston/liner fit.

J

Online Jo

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Re: Boll Aero
« Reply #2 on: September 12, 2014, 07:44:20 AM »
Chris Boll designed the Boll engine  ;) Ron redrew it in the Cad package so we have some decent drawings to work from.

Jo
Usus est optimum magister

Offline derekwarner

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Re: Boll Aero
« Reply #3 on: September 12, 2014, 08:04:10 AM »
Pete....the shank of an M24 diameter UNBRAKO Grade 12.9 socket head cap screw would be a perfect choice for this application

1. readily available
2. approx. 700 Mpa yield
3. easily machinable with a good surface finish
4. cost effective

Derek
Derek Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Offline Ramon

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Re: Boll Aero
« Reply #4 on: September 12, 2014, 08:30:29 AM »
Hi Pete - Jason has summed up the action of the CP well enough - just like to add that the fit is critical and is difficult to achieve to be 'just' right. 'Difficult' in the sense that's its easy to be too tight or worse too loose - if that happens you can hear the CP going up and down with the piston quite noticeably. Some advocate making the side walls on a very slow taper and the side walls themselves quite thin to allow a degree of spring - personally having tried it I don't favour this method preferring to keep the sides parallel and getting the fit right - As Jason says if you follow the thread on the Eta engines on here and the Eta and Tigre threads over on HMEM fitting these is well covered (and how to reclaim it if made too loose  ::))

Though I haven't made a complete crankshaft for any of these 5cc engines using a cap head bolt in it's entirety I have utilised them to make the inner part of the shaft on the composite shafts I favour. The material has proved relatively easy to machine with HSS tooling but it's better to screw cut it than to use a die - well certainly on these shafts which were 1/4 dia. Your much smaller shaft may prove much easier. The material strength will be more than sufficient to stand up to the stresses involved on this little engine.

Jason am I not right in thinking that the making of this engine (or something very similar) was covered in depth by Ron Chernich and Mike Rehmus in Model Engine Builder magazine?

Good luck with your build Pete, I wish you every success - it's a nice little engine :ThumbsUp:

Regards - Ramon
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Offline Jasonb

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Re: Boll Aero
« Reply #5 on: September 12, 2014, 10:17:44 AM »
You may be right Ramon, I'll have to look back through my mags to check.

They certainly did the Mills 1.3 and Humbug as well as the Lobo Twin.

J

Offline Ramon

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Re: Boll Aero
« Reply #6 on: September 12, 2014, 12:56:59 PM »
Ah - 'Humbug' Jason  ;) - that's the one I was thinking of.

Pete, though not really necessary, if you can get hold of a copy of this article (and it runs to several issues) it describes in great detail every step of the way for a first time builder of a small diesel engine.

Ramon

"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Pete49

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Re: Boll Aero
« Reply #7 on: September 13, 2014, 05:19:37 AM »
Thanks for the replies . I can now continue though I need to wait for some ali to turn up. A bugger when your nearest seller is 300 kms away :( . I have made  the piston, conrod, gudgon pin and now the liner. so far so good.
Jason and Ramon I think MEB is the humbug model and I have only the 1st issue from it but will get the others as they are digitised :D
Derek thanks for the tip will chase it up asp
Pete
I used to have a friend.....but the rope broke and he ran away :(