overheating damage

[rsumney]

last race my 06 yz450f overheated due to losing all my coolant. I got the bike started for a bit and then shut it down and pushed it out of the woods. when i put new fluid in the radiator it all leaked out where the radiator hose goes into the head. I just got a new o-ring for that fitting and am concerned that i may have done damage to the head. Anything else i should worry about or just replace the o-ring put fluid in and ride?

[mikedabike]

I had a buddy do this. The entire motor was shot. You need to tear it down and look at it. When my buddy did it the piston got so hot it seized like a two stroke would. The piston was actually melted.

[ttr250dude]

I had a buddy do this. The entire motor was shot. You need to tear it down and look at it. When my buddy did it the piston got so hot it seized like a two stroke would. The piston was actually melted.

i had the same thing happen on one of my snowmobiles. The rings were literally melted in the piston, you could see were the ring stopped and the piston started.

As for the rebuild, look at it this way: a top end rebuild is the perfect opportunity for a high comp piston

[STROKEDIESEL]

have you done a compression test yet?

[grayracer513]

have you done a compression test yet?

This is why Yamaha doesn't publish compression test numbers:

https://www.thumpertalk.com/forum/showthread.php?p=9556238#post9556238

[xr650r2000]

the cylinder would be scored

[STROKEDIESEL]

This is why Yamaha doesn't publish compression test numbers:

https://www.thumpertalk.com/forum/showthread.php?p=9556238#post9556238

i am aware of this! i would think that a known good bike decompressed compression reading to compare to his would work ok. its also hard to decipher from just words without seeing first hand exactly how long/hard the bike was run after initial boil over. only the OP would know this. if in doubt though inspect and swap it out. it will be cheaper that way in the end if it does fail.. all that being said i can kick my bike over with out the auto decompression working(it hurts though)

a roll down the driveway would also work.

[grayracer513]

A leak down test is far more useful.