I just bought a 1981 ATC 250r. Previous owner melted the piston, I took it in to have it fix and found the sleeve is for a 75mm piston.
Biggest Wisco I found is 72mm. NE1 know of a big bore kit that would use a 75mm piston?

 

I don't know of any off hand for the older R's. If it was me I would have it resleeved though. I don't know how good an that air cooled engine would do with that big of a piston. I am sure it would run but I just don't know for how long running with higher temps. All you have to do is look at the piston that is in it and you will see how the story will end.

 

Would it be possible to re-sleeve it back to stock? I totally would if possible, where would I look for that?
Thanx for your help too!

 

Sounds like it has a 300cc kit? I'm in the same boat.
There are no 300cc pistons avalible. I know a place that has one, but there $220.
The honda 300cc kit has a seven stud head instead of six. Then the fins on the cyl and head are huge.
heres a poor pic of one. You can see how the head is different than a stock 250.300cc pic

 

Contact L.A. Sleeve. They should be able to hook you up.

 

You might call this place in Milwaukie, OR
link

 

Took the cylinder to another machine shop today to see if I could get some more help. Turned out the dink at the first shop measured wrong. Its only a 71mm piston. Kinda bummed I dont have a big bore, but getting my $50 250r running looks a whole lot easier. Thanx for the help!