250-500cc 2009 WR250 Piston replacement

Hi

i was about to buy a spare piston kit with a bulk order from the US. I have a few questions.

1. do i need to remove the head to see if i need a type A/B or C piston in it? if so, will i need to replace head gasket or o-ring?

2. do you guys recommend OEM or wiseco, whats the difference? any good/ bad experiances?

Funny, when I had the 250, I was ordering my pistons from Stefan at R&D down under...

The truly proper technique is to pull the cylinder and mic it. You need to know how the cylinder measures, not the piston. BUT few people do and have no problems. The difference between an A, B and C piston is one thousandths of an inch each. If my cylinder was well broken in then I wouldn't think twice about running a 'C' piston in an 'A' cylinder. I've replaced my 'B' piston in my yamaha with a 'D' piston and no issues.

Wiseco doesn't even sell different sizes. I guess they're not too worried about a few thous either.

I like forged pistons personally. They are less likely to crack or explode like a cast piston can. They also seem to wear better and can be re-ringed to extend the life. I would not re-ring a cast piston.

The stock piston in my 09' wr300 was a cast Vertex, but I hear they also make a forged piston. Wiseco also sells a forged piston for your 250. That's what I would personally buy as I've had great luck with Wiseco.


Always, always, always replace used o-rings and gaskets. It's not worth the time and effort of dealing with a blown head gasket on the trail for $15 worth of parts.

That's my uneducated opinion!

I like Wiesco as well but they only make one size piston, they work but I have an E cyl and it gets looser sooner with the A size piston.
Pro-X makes the different size pistons as well.

how do you know the size of you cylinder other then measuring?

Excellent reply. thank you
I love this website

+1 not sure mate

Anyone used a woosner piston kit (forged) ?
are they good?
here's a link
http://wossneronline.com/forged_pis...ducts_id=455:dbacf1d7f3ae3fa29056d4f85279977e

also do the WR pistons have one or two piston rings?

2 rings for the 250.

The shitty thing, you have to remove the cyl and there is a letter stamped on the bottom.

not necessarily apparently, there are single ring versions for MX racing but they don't last as long i.e woosner single version

here's a pic

Is the CR 250 a single ring piston?

Yes i beleive so.