Boll Aero and Russian Factory Built

[byawor]

Engines are about the same size but obviously quite different. I have some questions or problem with the Russian engine.
1. The piston is very tight in fact won't pass completely through the cylinder. It feels like the cylinder was made with a very slow taper so the piston starts but tightens as it is pushed in. In the back of my mind I remember reading that this is the proper way to make it??
2. The contra piston is very small and a very tight fit in a recess in the head. Not sure there is enough adjustment to make any difference in the compression ration.
3.The rotary valve is not attached to the crankshaft?? There is a very fine slot in the face of the valve and in the crank maybe there is supposed to be a pin inserted to join the two parts. Can't see it working but maybe

 

[Mechanicboy]

No fault with tapered cylinder due expansion by heat. Hence the piston feel tight in TDC. The contrapiston must be tight in cylinder, but movable by compression/adjustingscrew. No, the rotary Valve is not fasten to crankshaft. Also no fault with russian engine.

 

[byawor]

Piston is so tight engine can not be turned past tdc. I think I will hone cylinder just a bit. I don't understand the rotary valve. If it does not turn with the crank how does it function?
Bob

 

[byawor]

Contra piston also very very tight if it is forced into recess screw will not move it

 

[Mechanicboy]

No, do not hone cylinder! Clean up the contrapiston with steelwool due old castoroil and mount into cylinder + oil on surfaces. The crankpin is rotating the rotary valve who has recess for crankpin.

 

[Mechanicboy]

Mount propeller and flip the engine and piston will go past TDC. Not with fingers on crankshaft.

 

[byawor]

Got the piston fitted. I see the pin for rotary valve. Should the slot in valve be pointed to the pin or away from it?

 

[Mechanicboy]

The crankpin must have same fit in the slot. No wide and slopppy. It can be 2 slot for forward or reverse direction of rotating. The rotary valve into the backcover with carburator.