1982 250R pic of jug.. need piston size?

[wpginterceptor]

OK, I just purchased this jug for my 82 250R and it looks great.. just need to know what piston size I need to put in there etc? does it need to be bored out still? YES im currently rebuilding the top end!
PS: the inside of the bore looks great, NO scoring or anything. CLEAN AND SMOOTH. should be able to drop a piston and go! BUT WHAT SIZE?? do I have to bore it out to next size for a good fit?

[82 250r]

Weisco makes a forged piston for that 82 but they are getting expensive. Don't "drop a piston and go". Spend the $65 and have it bored to the next size up. The machinist will tell you what size to get.
70mm is the stock bore size so don't be afraid to do it right. Just imo.
When you get the right size from the machinist, ebay has the best prices for the piston kit.

[wpginterceptor]

So what is the next size? like it shows in the pic 70.40mm is the current size now

do I go with a 72MM piston? is that the next bore size?

[82 250r]

Don't know.
They USUALLY make them 70mm, 70.50mm, 71mm, 71.50 etc.
You need to know the clearances, bore condition, available piston sizes etc. That's why you take it to the machinist.
If you drop in a piston, get the stock 70mm, but like i said, they are expensive. You will have too much clearance for a stock piston and the rings will not seat without a hone.

[wpginterceptor]

mine sounds like a 70.50mm piston should work!

[82 250r]

How do you figure?
Do you know the clearance for an 82 to be .10mm?
btw...you don't measure a bore with calipers. That only gets you in the "ball park"

I'm not trying to be a dick, but you are lucky to have a stock bore jug and it sounds like you're about to waste money on a piston and later a bore that takes out 2mm just to fix your mistake.
Just trying to help.

[toki]

bores can wear out funny as well. you have to remember that the top of the bore doesnt see the same forces as the middle and bottom. measuring side to side can change compared to front to back measurements. best to take it in, have a machinist measure it with a bore gauge, snap gauge and mic, whatever they do. air s kick ass by the way.

[wpginterceptor]

relax, lol.. I haven't done anything yet... that's why im here to find out! and yes I don't have a proper guage to measure the bore.. was just using this as a ballpark!

My old jug bore I measured with same caliper and got almost 72mm

[DohcBikes]

This is the second time you have posted a thread about this engine. The first time you said.....

Took apart my 82 250R today to order a new top end..

question is..

What is standard size? I measured the piston I took out and got 71.70mm (by the skirt)

Please put the Very Near caliper back in the case. There are zero reasons to use it when building an engine.

There's so much going wrong here that I think it's best if you just pay somebody to build it.

[wpginterceptor]

don't need it built.. just need it bored! don't have the equipement, and yes im just gonna send it to the shop and they will bore it.. Rest I can handle