Hello friends,

Yesterday I bought an NIB OS 25FX from a local hobby shop. When I came home instilled some after run oil drops and installed a prop.

I begin to turn the prop by hand, but when piston is in up position, there is a lock something like a short stroke, then I need to apply some force to complete the turn.

I did put apart the cylinder head and cover plate and inside the engine seems to be new. When I release the cylinder head screws, this lock or short stroke disappear.

There is something wrong with this engine, should try to break in or should to return to store?

Thanks in advance.

Javier