Rebuilding Guide?

[LocoParaHonda]

I was just curious if there was a guide online somewhere about how to completely rebuild a Honda Aero/Elite/Spree 50cc motor?

Couldn't find anything in the tech docs, seems like there should be somewhere. I know it would be a lot of steps.

[Kenny_McCormic]

Off the top of my head.

Tear it down
Check the big end rod bearing, if loose crank will need replacement/rebuilding.
If bore is scored deeply, it will need to be bored.
Replace piston if scored/overbore is required, if piston/bore looks good, just re ring.
Check oil pump, replace oil seal if needed
New crank bearings and seals
New little end rod bearing

[noiseguy]

Above list is great. I'll add a bit to expand on it:

Frankly, few people will completely rebuild a motor like this, unless they're doing a complete custom job (new crank, etc.) It's rarely warranted to do a full rebuild, unlike, say, a Chevy smallblock, where you pretty much replace all the stuff at the same time. You just fix the issues as they arise. Instructions are in the factory service manuals.

If compression is shot, pull the jug and take a look to see what the problem is. You can inspect the lower end bearing for play at this point, or by measureing if you remove the piston. Frankly, if the lower end rod bearing is shot it will be cheaper to find a complete used engine in better shape most of the time. The lower end bearing is difficult to replace and most guys will run down a different block or used crank. Of course that's only true if what you buy is really in better shape than what you have

While we're inspecting things, did you hear bearing noise in the engine before teardown? Hard to say if you don't know what it's supposed to sound like. If so, remove the sidecover, grab the front pulley and see if there's fore-aft / vertical play. If so, you need new crank bearings. This is more difficult than jug/piston work but still easier than replacing lower end rod bearings.

Checking oil pump operation is very important. I'd do it before teardown if the engine is still running, otherwise 1st thing after rebuilding.