Hello , I built a small little extra-10 3-D plane and it called for a 15 size engine. So I put a OS 15 LA on it and its not enough power for me, So then I got a new OS 15cv-a And my question is this new 15 cv at top dead center the crank shaft moves a little bit and the piston does not. Like a 1/8 to 1/4 of an inch with out the piston moving ! Is this nomal and just needs broke in? The 15LA does not do this. Maybe its a bad engine? Doesn,t OS start and run all there engines before they sell them ? Any one heard of this before ?

Basically, yes. At TDC the piston feels like it's "bound" up at the top of the cylinder, allowing for a small amount of slop in the crankshaft. The cv-a I'm sure has more "pinch" than does the LA.

You're feeling a little bit of "over the center" snap caused by slight flexing of the connecting rod/piston assembly.

Thank's for your input !! Today I took it back to the hobby shop and the store owner kind of chuckled . He said It just needs to be broke in ! Run it rich and I'm good to go ! The 15 CV-A has a bigger carb and more compression than the LA And more RPM's as well. Thank's again.

It is a great engine, feed it it 20 to 25% nitro and run a 8x3 or 7x5 .

don't run it so rich it doesn't get up to normal operating temp. You want it to break in, not wear out the piston / sleeve fit prematurely.

Search around the threads for tips on breaking in ABC or similar type engines.

You have a fantastic engine in the 15 size-maybe one of the best. Don't worry about anything regarding crank slop, conrod bending,ect.... hogwash. Run it slightly on the rich side for a few tanks being sure it transititons and idles well. 15% Nit. fuel and up works well-18%+ oil. Have fun with it-twice the motor of the LA.