I was just wondering if anybody has had any cooling problems since they bored there 400EX to a 426? That is the only thing holding me back on buying that piston, I don't want to get an expensive sleeve just to keep it cool.

 

Talk to some engine builders, the cylinder wall is getting very thin with an 87mm (416) piston, yet alone the 88mm. I believe the reputable shops are sleeving 426's

 

It cost me $500 for a 453cc kit withg LA Sleeve, your better off sleeving it. $500 was everything including Weieco Piston and rings, LA Sleeve, Cometic gaskets, and even labor. I though it was a good deal! MIne is trail ridden and never gets hot on even the hottest days.