Ringed engine compression both directions
 

I've never started a thread on here before but I've noticed that on several of my ringed engines, the amount of compression they have feels different if the engine is turned counter clockwise compared to turning the prop clockwise? I have my own idea's as to the cause but I would like to hear some other thoughts on this?

I have three identical Custom Lee K&B 61's two of them have better compression if turned counter clockwise and the other is just the opposite. All three run fine.

I have a Magnum 120 4 stroke that has excellent compression if turned counter clockwise, but almost none if turned clockwise. These engines are all relatively new. I also have two Magnum 61 four strokes and they are both the same either way.

For you real guru's, I have some ST 40, 51, 61, & 91 engines that are the same either way. This should tell you why?

Ringed engine compression both directions
 

the only theorie that i have is maybe the piston/ring assembly enters the sleve at a slightly different angle depending on the direction that the crankshaft is turning..

if the engine is broken-in in a certain direction.. the little abrasions on the piston and sleeve will fit one way.. but not in another??

Compression
 

I believe this is due to the ring, ring land and piston skirt wearing differently on the exhaust side, the rod angle pushes the piston toward the exhaust side on the compression stroke and away from the exhaust side on the combustion stroke. It's not the timing because the cylinder is full no matter which way you turn the crank. You won't notice this difference on a non ringed engine.

Thoughts
 

Well, my thoughts on this are that the ring gap is towards one side of the piston and the piston skirt will seal the compression in one direction but not in the other because the piston will actually rock back and forth as it moves up and down in the cylinder... Depending on which direction the connecting rod is pushing on it. But it does seem to also be an indication of ring gap?

The Super Tiger engines have a pinned ring that the gap is most likely in the front quadrant unless someone put the piston in backwards. So it will have the same compression either direction.

GelCell and hobbsy have reinforced my suspicions and were the responses I was looking for.

Thanks,

Jim