I am rebuilding my trainer after plowing it straight into the ground. I didn't think the engine was damaged (no binding or sticking), but after I mounted the motor I realized it spun too easily like the compression has dropped. Any idea what has happened?

balsacrackerx10:

Check the glow plug and the head screws. Have you checked to see if the piston moves? While the plug is out hold a toothpick in the plug hole, turn the crank and be sure the piston does move. Very rare but I've seen a crank break cleanly at the intake port, prop turned nicely but the piston didn't move.

Most likely it's just dry from your cleaning it. Try starting it and see what happens.

Bill.

It still has fair resistance but it will not come around and smack my finger hard like it did before the crash. I thought that if it was damaged it would probably be harder to spin.

BC:

As I said, just run it and see what it says.

Also, if you are running synthetic, try the Omega 15% nitro - it's part castor oil, helps seal things when they get a bit loose.

If that last flight was a lean run, the engine could be damaged and have the damage bear no relation to the crash.

Just use some castor, run it and see.

Bill.

When your plane crashed, how much dirt/debris did the engine ingest? You may have had some lodged in the valve seat or your valve lash may need adjusting?

Happy Fly'n....

I lost compression once......glow plug was broke. It looked ok but the center "pole" was broken away from the housing.