briansgi,
I know you're a very knowledgeable person concerning the R as I've read many of your posts on the 250R forum. If you're like me, you don't mind being told you're wrong if you are, 'cause I like to learn an be updated.

The only way that you can be running .100 / .110 over on an 88 cylinder is if you had the jug bored and resleeved. That way it is possible to continue to get larger bores, all the way to a 310 cc motor; that is also the only way to get any R cylinder up to that size.
Just 'cause you run an 86 piston in an 87-89 jug won't let you bore larger; there just isn't the material in the stock sleeve to allow it.
Look at it this way; if an 88 cylinder can only go .080 over running a 88 piston, why would it suddenly be able to go up to .140 just because you want to run the 86 piston? Please tell me.

Anyway, from my experience, I've run with all years of Rs, and as far as power is concerned, I've not seen a noticable difference in any of the years. It's all what is done to them aftermarket that makes the difference.

 

Not to beat a dead horse here but to back up what Trapper is saying, check out these web sites that sell Wiseco pistons for the R:

http://www.carbidesmotoworld.com/cgi...wisecoatv.html
http://www.moto-man.com/cgi-bin/mtm/search?Nn2M7nIV;;3

Notice the largest piston offered for the '87 - '89 cylinder is .080"!! Like Trapper said, the only way you can run a larger piston in a "true" '88 cylinder is if it's been punched out and been resleeved.

 

You can bore a 87 through 89 250R cylinder to .140" over and use a 86 style piston in it with a spacer plate and the factory *long* rod , or , if you use a *short* rod you can leave out the spacer . Holding a head gasket on one is best done by machining a solid metal gasket I.D. to match the bore .

On any year cylinder by the time .140" over comes around things are getting thin . On an 85-86 the intake skirt is what is most apt to failure (it will break off) , on an 87 - 89 the intake bridges are most apt to chip and cause the engine to fail .

Big bore sleeves for all years have the same O.D. dimensions If you decide to install one in an 85 - 86 you will have the most success using the 87 - 89 style sleeves . The added intake ribs will keep the piston more stable and less prone to cracking .

 

machwon and RickRitter,
Well, I gotta admit it!
You two were correct! I was wrong.
You can bore the 87-89 up to .140 over.
You are correct that using the 86 style piston is the only way you can run cylinders bigger than .080 over because no one makes them for 87-89 for some reason, and only the 86 style is available.
I own an 86 and an 87, I knew about the differences such as the rod length/piston style. I just thought that you were limited on bores on the 87-89 models.
Thank you.

 

hey its rick ritter. good to hear from you. are the 86trx cranks the same as 86atc cranks?

 

The rod length is the same . The only differences I can recall are a PTO end length change in the later year quad cranks .

Please correct me if I am wrong .