Roby

I got this engine 2 years ago , never ran it until I
got it mounted to the airplane it was intended for.

I have about 1/2 a gallon of fuel through it using the typical
break-in procedure. It seems to run fine but one of the
cylinders is off a little on compression as compared to the other.

Has anyone else experienced this ? Or does this engine have a
long "run-in" time as compared to other 4 strokes ?

It has more than enough power to pull the plane around
so maybe I'll just fly it on the rich side for a while and see
what happens.

Thanks to all who respond.
Roby

Waco Driver

I have been running the OS 120 II twin for 13 years and have the same uneven compression situation. I have noticed it on both the OS 160 twins and also the 240 four. It is caused by the difference in location of the ring gaps. If the ring gap on both cylinders is on the thrust side of the piston, or on the other side, or both forward, or both aft, compression will by the same on both cylinders provided that the valves are all seating normally. However since the rings are free to rotate while the engine is running, the ring gaps become staggered resulting in the uneven compression situation. Don't worry about it. It is a normal.

Roby

Thanks Waco Driver

I flew the engine for the first time this weekend and put
an additional 1 hour on it.
It was flawless. At the end of the flying session I had sort
of determined that the compression difference was not going
to be an issue. I do very much appreciate your "validation "on this
subject. As you can understand, I was a little concerned.

Regards
Roby

bigben

My Feedback: (24)

I'm working through the same compression difference and just changed out both rings to improve the low cylinder. Seems to be helping but just getting to the break in stage. What have you learned on your engine since you wrote this post?
Thanks for sharing.

summerwind

i've had 2 of the ft160's and 1 ft240 and ft300 and all were the same.........great compression on one cylinder, mushy on the other when flipped forwards.......flipped in the opposite direction though and the mushy side has strong compression.
Waco Driver descibed it 100% correct......it all has to do with where the ring gaps are.

all 4 engines ran like clocks, and never have i felt smoother running engines than OS twins.

i'd give my right arm if OS would produce an equivilant to my Laser 200V..................their twins are just so smooth.