I need help

[levi400ex]

do I need to bore out my cylynder if I put new rings in my 400 ex as long as the cylender is not bad.
I ask this because this would be my first top end rebuild and I should no this but I do not.
I just want to make shure I am doing every thing right.
thank you

[BLEEDRED]

You probably don't have to bore the cylinder if it's within the service limit. But you HAVE to have the cylinder honed so the rings will seat properly.

[Silverfox@C&DRacing]

I would take it to a machine shop and have them measure the cylinderwall to piston skirt clearance, if it is with in spec I would have them rehone it and replace the rings. if its not with spec its time for more power :p :blah:

[wilkin250r]

Wow, this is a funny question I've never dealt with on a 4-stroke. Of the few 4-strokes I've rebuilt, I was always overboring.

The 2-strokes will go through several pistons in a single bore. It is very common on a 2-stroke to hone the cylinder and replace the piston (and rings) without overboring.

Is it common on 4-strokes? Do you go through multiple pistons on the same bore? I don't see any reason why not, the aluminum piston will obviously wear much faster than the iron cylinder sleeve.

[RiderTRX400ex]

while your going as far as tearing it down that far.. just get it bored with a new piston... wont hurt anything.. cheap.. and some gains

[wilkin250r]

Maybe that's the answer right there. With less frequent rebuilds, available overbores aren't quite as valuable, so wasting bores isn't a big deal.

I can't imagine overboring a 2-stroke every time I rebuild. I'd be spending a fortune on re-sleeves, spare cylinders, and porting!