XR250R max bore dia. stock sleeve

[jjpete86]

I posted this on the xr250/400 thread but no help.

 

I need my cylinder bored, looking to go as big as the stock sleeve allowed. I've seen kits for 77mm but I've seen 78mm Pistons. Will the stock sleeve allow a 78mm?

 

Next question

After I bore my cylinder, does my head need to be milled for the piston?

The Pistons I've found have cutouts for the valves.

 

 

[BOAB]

I have a 2003 with a 77mm bore (277cc).  I would not recommend any bigger on the stock sleeve, as it is the 77mm bore leaves a very thin sleeve.  A thin sleeve will cause your bike to overheat, or at least run very hot.  You do not need to do anything to the head.  After break in run a high quality synthetic to make the bike run cooler, I run Lucas 20W-50 motorcycle synthetic.  I highly recommend Wiseco pistons.

Edited May 1, 2017 by cjjeepercreeper

[jjpete86]

I have a 2003 with a 77mm bore (277cc).  I would not recommend any bigger on the stock sleeve, as it is the 77mm bore leaves a very thin sleeve.  A thin sleeve will dissipate heat slower and cause your bike to overheat, or at least run very hot.  You do not need to do anything to the head.  After break in run a high quality synthetic to make the bike run cooler, I run Lucas 20W-50 motorcycle synthetic.  I highly recommend Wiseco pistons.

Thanks exactly what I needed to know, what oil should I break it in with?

[BOAB]

4 minutes ago, jjpete86 said:

Thanks exactly what I needed to know, what oil should I break it in with?

High quality dino oil, Honda oil, non synthetic, would be a good choice.

[BOAB]

And I actually somewhat misspoke in my original post.  The thinner sleeve doesn't dissipate heat slower, it actually leaves less of a heat sink.  Effect is the same, though.  We were having a discussion about the cooling system in my son's Cherokee and my brain was still there.

Edited May 1, 2017 by cjjeepercreeper