I need to replace my piston and rings on my atc. Where can i find a big bore kit for it? Will it make much of a difference? It is air cooled and i am worried about heat. Will it make it hotter the more i bore it? Thankyou for your help.

 

Honda made a 300cc factory kit. I've seen them on EBAY. It'll probably take some time to see another one, but I'd check there regularly. I don't think that there will be any temperature difference from a larger piston, so I wouldn't worry about it. I had an 84 250R and ran it very hard and never maintained it (I was 15). It ran like a champ and I never melted the piston.

 

I am in the process of restoring an 85' atc250r, you might remember earlier post. Well I took my cylinder in and they said they will see what they can do, it will depend on how deep the rust goes, so if it works it will have a bigger bore. Is there any other parts of the motor beside carb and exhust that must be modified to go along with it?. 4 strokes ussually need a new cam and valves.

 

i just bought a couple of 84s one came with a 300 cylinder and head. if you find any good info keep us informed.

 

I also got an 84 ATC 250r. Two years ago I had the cylinder bored 80 over, I had to keep stopping to let it cool for a while. Anything over 40 over is to much for an air cooled motor, at least mine was. It kept sucking in the base gasket.
Since then I have found a brand new 300cc kit for it and love it, I can ride the bike all day with no problems, and I don't take it easy on it.

84 ATC 300r, 86 ATC 200x