2002 rmk 800

[CamoKVF700]

Sold my buddy my 800 a few years ago. Ran great for 3 years. He took out the top end this year (detonation) die to running it with last year's gas in it. He rebuilt it and put new 91 pump gas in it. Didn't ride it long and this is what happened. ... Any ideas what caused this?

Both cylinders appear to be the exact same damage. Exhaust valves hanging up? He said he serviced those.

Where's the cheapest place for cylinders and pistons that you know of?

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[andrew3399]

Dirty carbs. Torn intake boots.

 

[CamoKVF700]

Dirty carbs, can you explain why you feel that could be the issue?

Torn intake boot would mean lean. This doesn't look like that bad of a lean condition.

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[timbo]

Looks like pistons are in backwards?Arrows should face exhaust.

 

[CamoKVF700]

Good point there. I overlooked that. I have just the pic. Gotta make it over there to have a closer look.

Do these pistons have a thrust side or a pin slightly off center? That would explain a lot

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[Trashy]

Take the cylinders off, and check the free play on the connecting rods. The piston on the right looks like my old Rev, when the crank bearings let go.

 

[timbo]

Ring ends will catch a port if in backwards and break piston and chip the port.You will see when taking apart.

 

[CamoKVF700]

I sure hope the crank bearings aren't shot. I hate messing with the bottom end

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[CrankShop910]

The pistons were installed backwards, you can see the ring locating pin in the pic..
The arrow allways points to the ext side. That's a ****ty deal.