Do I need a bigger piston to rebuild my 300 ex

[synctothebeat]

I finally got my 300ex running after it sat for like 4 years. It starts up and runs fine, it just smokes horribly all the time. I'm guessing it probably the rings. I want to rebuild it as cheap as possible, and would prefer to do it my self. I just wanted to know if I needed to get a bigger piston like .20 over or if I could just Use a stock bore piston. Thanks, any comments or advice would be appreciated.

[JIMFROMTEXCO]

you wouldnt be able to tell untill you tore it down. if the cylinder isnt all messed up you could prolly get away with a fresh hone.

[TRX-330]

What he said^

OR it can be a number of things the color of smoke will determine the problem.

Black- Gunked carb from sitting to long. Disassembly and a good cleaning should take care of it.

Blue- Valve stem seals may be the most logical starting place.

Grey or White- Bad rings, new rings and fresh hone should do the job. Unless cylinder is worn then bore it or re-sleeve and new piston with rings will take care of it. Id say to go the smallest amount over with a bore job. Your cylinder might be worn but not BAD enough to bore, you could get by with 1/4-1/2 over rings and file the ring gap down to where Honda requires it to be at.


Hope that helps some.

[JIMFROMTEXCO]

if it was the carb it wouldnt smoke constantly. it would eventually clear up.

i personally woulndt buy just new rings if i had it apart i would go with standard bore wiseco piston 11:1. it makes the bike wake up

[bwamos]

I'm betting he's got bad valve seals.

I'd do a leakdown test. Pretty easy to find the leaks when you do that.

Could even be a torn head gasket in the small areas between the cylinder and the oil returns.