Bored Cylinders

I was wondering if anyone has bored their bikes when they did the top end? The reason I ask is that I have an extra cylinder, and to have it bored and re-lined is the same as getting a new one. I know that wisco sells an 80cc over piston for it. Any input would be appriciated.

Later- The Fireman

Sure would be nice to know what bike we're talking about.


MX Tuner

Originally posted by MX Tuner:

Sure would be nice to know what bike we're talking about.

I would think, assume rather, that since this IS the YZ426 forum, he *might* have a YZ426...but that is just an assumption...

This is the YZ400/YZ426 forum.

Tuner's 420 and my 444 are not covered in this group.

I installed a 420 kit in my '99 400 and love it. Yes it is same cost as original 399 cc. Reliability may be better as aftermarket replating tends to be more durable than stock. I would stay away from a sleeve, a re-chrome will give better performance for heat transfer and reduced friction.

An 80cc over piston? Hummm....

Seems like a big step for a bore job. Wouldn't that make it a 506cc bike? Yikes!

Could this have been an .080 over piston instead?


He said 80cc over. Does this mean an overbore for a YZ 80? Does it mean .080" over? Does it mean he wants an 80ccs over a 400? a 426? I was just trying to get some facts to work with.

Oh, and Hick, I also have a 97mm slug in my WR. No cheesy little 95mm piston for me.


MX Tuner


Do you have the 13.5:1??

I think he means .080" over, or 2mm.

During my heavy days, it was a common practice to match a bore job to an exact piston size, since all pistons varied in size, slightly.

I'm talking very small amounts of course, but in V8 engines, you assigned a piston to each cylinder and bored respectively.

Do they still do this?


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