1st rebuild on 2 stroke ?'s

[mbaird]

I just tore my 03 CR250 down yesterday and took the clyinder to the shop. They told me I should replace the piston
when I do a rebuild. I am OK with that as the skirt looks a
little worn. My cylinder is an A, so he got a Pro-x piston (a)
off the shelf , inserted it into the cylinder and kind of eyeballed it.
I know that when I build a 500hp V8 piston fit is crucial.
But I am new to 2 Strokes. Is this OK ? Or should he be
measuring the bore.

Also, any advice on piston brands etc... I mainly trail ride,
( at a fairly aggressive rate !) and dont want to have to tear the bike down 4 times a yr.

Thanks for your input

 

[mandark1967]

Fit is, indeed, important when rebuilding any internal combustion motor, regardless of how many strokes it was.

Maybe the piston the shop guy grabbed was a special order that someone put a deposit on and didn't pay for so the shop had one available in stock that was for the same bike? (just a guess...but sometimes you get lucky that way)

You do want to use a mechanic who actually measures the bore and then determines the proper piston.

I'd call the guy and ask him if the piston he eyeballed was made for your particular bike.

If you are a trail rider (and an agressive one at that) you should be able to go a couple years before rebuilds.

I'm particularly biased towards using wiseco brand pistons myself, but there are other good makers out there so have a look around at some of the websites like dennis kirk (to get brand names) then do some research on the ones that interest you most.

 

[mbaird]

I got my cylinder back and a new piston (pro-x A ) . There is
.004 clearance between the piston and bore. I am not sure if that is too tight or not. The guy used a rigid hone on the cylinder, which I am not happy with. I assumed he knew to use a ball hone , he say they catch the ports .

Any feedback on this would be appreciated.

 

[Oldman125]

...a ball hone , he says they catch the ports .

Any feedback on this would be appreciated.

That is correct.