I just re-assembled my o.s.18cvr-m and it had some scratches on the piston and liner and now when i turn the crank with my hand I do not have a good tight fit when the piston reaches the top of the liner.

The engine only has a couple quarts thru it and should still have good compresion.
I was told that with the head off when you turn the engine over it should almost push the liner out of the block..

Is this engine now shot.

Terry

If the engine doesn't have any 'grab' when the piston's at the top of its travel, and the engine's cold, then the piston/liner fit is gone. R/C car engines tend to wear out very quickly because they tend to get overheated or dirt-damaged. It's not an inherent problem with the engine, but a result of operation and operating conditions.

Scratches on the liner mean that foreign material has gone through the engine. Mild vertical scratches on the sides of the piston are normal. If the aluminum sides of the piston are a dark gray color, it means that dirt's gone through the engine. If you see a lot of scratching on the crankshaft under the carburetor, it also indicates dirt ingestion. The case inside, under the carb, after you remove the crank, would have a lot of scratches, too.