How can you tell when a motor needs a rebuild?

[davetfft]

I've got a couple motors I think need rebuilding because they simply do not run or start reliably. They start incredibly hard (compared to my newer engines) and when they are running they stall easily. No amount of tune seems to alleviate the problems as well and I do believe I've gotten tuning figured out. My other x4.6 will start instantly, rarely stall, wheelie all day, puffs light smoke and runs great so I think I understand that aspect.

I do feel some compression resistance when turning it over but how can I confirm a rebuild is needed?

Thanks!

Dave

 

[Chumlee]

I always go by the "pinch"

You can tell a big difference in compression from a new engine and a worn engine. I also check the top of the piston to make sure it has been burning right. Air leaks and improper tuning can cause a "varnish," to build up on the top of the piston. I use after-run-oil but I try to keep the engine clean too. The oil will build up and cause issues too if it is not cleaned out of the engine properly. I like dipping my engine's in alcohol or putting a few drops in the carb and a few on top of the piston and turning it over to make sure the oil doesn't gum things up.

Hope this helps,

J.T.

 

[davetfft]

I'll give that a try, thanks!

 

[Macguyver]

just dont leave alcohol in the engine ...alcohol attracts moisture and could rust the inside...i use WD40 ...it wont gum up and will remove any moisture