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Boll Aero

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Graham Williams 519/06/2018 10:34:42
98 forum posts
9 photos

Does anyone know if there are errors in the published plans for the 1.8cc Boll Aero engine. Finished one some time ago and just got around to try to run it but not a peep out of it. Both piston and contra-piston fit are really good and I've stripped it down to re-measure everything and it looks ok, any ideas????

cheers Graham W

geoff walker 119/06/2018 15:20:43
412 forum posts
159 photos

Graham there is another thread in this forum, have you read it, may help you.

Keywords Bollaero glow plug engine


Graham Williams 519/06/2018 16:04:36
98 forum posts
9 photos

Hi Graham. That's a different engine altogether, its an approx. 8cc glow engine, mine is a 1.8cc diesel engine, both called Boll Aero..


Graham W

LADmachining19/06/2018 16:24:52
103 forum posts
10 photos

Does it draw fuel to the carburettor if turned over with a finger covering the air intake?

Do you get any signs of life if you prime it (sparingly!) directly into the exhaust port?

From the number of completed examples that were shown on Ron Chernich's website ( I don't think there were any show-stoppers in the plans. What date/revision plans do you have?



daveb19/06/2018 17:13:34
622 forum posts
10 photos

Small compression ignition engines can be difficult to start, an electric starter motor would make life easier. I still have the scars from the one I had over 50 years ago.

Graham Williams 519/06/2018 17:40:05
98 forum posts
9 photos

Difficult to see if the fuel line is filling as its a black one, primed the engine to see if it'll fire if not run a number of times and avoided flooding it but there's nothing there. Turned a spinner and tried an electric start, which I always think is a bit dodgy with a diesel, but nothing, changed the fuel as well though it runs an ELFIN perfectly well. Plans are dated 17th August 2009. Just not seeing what's wrong with it.


Graham W

Old School19/06/2018 17:45:29
335 forum posts
29 photos

For little diesels you need new fresh diesel fuel if you are going to have any chance of starting it

Howard Lewis19/06/2018 17:52:10
3267 forum posts
2 photos

LONG time since I had anything to do with small two stroke C I engines, but just a few thoughts.

Are there no leakages? (Presumably the carb feeds into the crankcase, so if there are leaks, it is unlikely to draw fuel into the crankcase. Crankcase must be airtight, as must the crankshaft/main bearing fit

Is the transfer port a) in the right place (Rude!)

Is the piston flat top, or curved? If curved, is it fitted the right way round?

But if it does not try to fire, is the compression ratio too low? Which implies either the contra piston is too short, or the compression height of the piston is too short.

It ought to start and fire by flicking the prop over. YEARS ago, my Mills 0.75 did.

Since your ELFIN runs OK, the fuel is not the problem.

Let us know how you get on.


Mike Blankley19/06/2018 17:55:45
14 forum posts
12 photos

I have built this engine and it ran ok. You should not use an electric starter on a Diesel due to a possible hydraulic lock. Does the piston completely uncover the exhaust port on the down stroke and uncover the inlet port on the up stroke? You need a really good piston fit with no ovality which should give a really good compression. Good luck.

Graham Williams 519/06/2018 19:00:00
98 forum posts
9 photos

Howard. Crankshaft lapped into front housing and both front and back-plate are sealed with gasket cement so no leakage that I can detect. As near as I can measure all the dimensions to the plan are accurate so I was expecting it to be ok. The piston doesn't uncover the exhaust port completely though. The conrod length, crankpin to crankshaft centre, piston height and gudgeon pin centre all to plan. The only thing I haven't checked is the crankcase top deck to crankshaft centre, will check that in the morning, had enough for today lol.

Cheers Guys.

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