Piston ring stuck right after rebuild. Any ideas?

[sledfanatic101]

Rebuilt the engine on my buddy's 2013 polaris pro rmk 800. Broke it in right. 4 heat cycles and then started driving it. 9 miles later a ring stuck and broke. l primped the oil pump before we started it. Also ran 30-1 oil in the tank for the heat cycles and then 50-1 when we started riding it.

 

[Jay]

just curious, what type of pistons?

 

[sledfanatic101]

Kimpex

 

[05rmksteve]

Did the locator pin fallout? I've never used kimpex pistons but if the quality of their pistons are the same quality as other kimpex products that could be the problem. Poor quality.

 

[RHODESIE]

are those keystone rings? or are they perfectly flat. pics make them look like keystone. i saw that happen when a guy had one installed upside down.

 

[05rmksteve]

After looking at the pictures a little more it does look like both locator pins are still in place. Was the ring end gap checked? Was the cylinder re-plated I've heard of some issues with the re-plating company's not chamfering the ports enough and causing rings to catch.

 

[ditch1000]

Go with Wossner pistons and don’t look back..

 

[Jay]

Kimpex

thanks

 

[BeartoothBaron]

+1 on the ring end gap - that'd be my chief suspicion. It'd run fine until you started putting more load on it, then the ring would bind, start grabbing, and break. A ring upside-down could also explain it (incidentally, one fringe benefit of Wossner pistons is I don't think it's possible to get the piston in with the ring upside-down). Also, Kimpex may be the same thing as SPI and maybe another brand or two. If it's made in Taiwan, it probably is, and I hear they can be a decent piston. Probably not what I'd pick though. Whatever the case, It's definitely a bummer to have a new top end go nowhere like this...