Slightly milky Power Valve… Bad Cylinder Head O-Ring?

[Troutfrea]

Greetings,

I think the title is self exlpanatory. Bottom line; I noticed the oil on my PTO side power valve seems slightly milky. Not bad but it does seem different than the mag side. What do you all think? Should I be concerned? Do you think it’s an o-ring? Something else? I really am over this sled giving me issues. This is for a 2012 rmk 600

More detail… I just rebuilt this motor and it has 70 or so miles on it. It shutdown when my daughter was on it over new years. It wasn’t hot (around 130). The motor didn’t want to spin initially but broke loose and my buddies mixed oil in the fuel and dumped oil in the cylinders ( I wasnt there) and she was able to ride it home. It still has 90 pounds in each cylinder so I’m hopeful the motor is okay. Just need to understand what is up with this cylinder.
Separately, I need to figure out why the motor seems to be starving for oil. I’ll start a separate thread for that if I can’t find anything.

Thanks in advance for your help!

 

[BeartoothBaron]

The oil on the shaft in the first photo does look a little milky, but not bad enough that I'd say definite coolant contamination. I suppose it wouldn't be terribly expensive to replace the o-rings; the other possibility, if it is coolant contamination, is the water pump seal. That's a bit more pricey and a lot more work. If you can get to the crankcase plugs, you'd definitely want to open them and see if you get any water. 90 PSI is pretty low; I'd be concerned if that's what I saw, but depending on the tester, methods, and elevation, it's possible you could get that on a healthy motor. The way I do it is pull both plugs, put the tester on, hold the throttle open, and pull the rope until the needle stop rising - then repeat with the other cylinder. The shut-down you describe sounds kind of like a four-corner seizure; did it happen shortly after stopping a while?

 

[Troutfrea]

The oil on the shaft in the first photo does look a little milky, but not bad enough that I'd say definite coolant contamination. I suppose it wouldn't be terribly expensive to replace the o-rings; the other possibility, if it is coolant contamination, is the water pump seal. That's a bit more pricey and a lot more work. If you can get to the crankcase plugs, you'd definitely want to open them and see if you get any water. 90 PSI is pretty low; I'd be concerned if that's what I saw, but depending on the tester, methods, and elevation, it's possible you could get that on a healthy motor. The way I do it is pull both plugs, put the tester on, hold the throttle open, and pull the rope until the needle stop rising - then repeat with the other cylinder. The shut-down you describe sounds kind of like a four-corner seizure; did it happen shortly after stopping a while?

Thanks for the reply. I tested the cylinders the same way you described. I’m around 5000 above sea level.

A four corner seizure sounds terrible. What exactly is that?

The shutdown happened about 10-15 minutes into the ride. They were cruising down the trail around 25-30 MPH.

 

[BeartoothBaron]

Four-corner seizure is the result of a piston that's too tight in the bore, not letting a sled warm up enough before riding it (especially if you jump right into high-throttle riding), or a combination. What happens is the piston expands too much relative to the bore and seizes; with high load on a cold motor, the piston will heat up and expand too quickly relative to the colder bore. It leaves rectangular marks in the bore (opposite the piston pin). Sometimes it does little enough damage that the engine will run fine again, but it's more likely to ruin the motor. What you describe doesn't typically make for four-corner seizure unless the sled was overheating. Do you have the y-pipe off yet? You should be able to get a good idea of what's going on by looking down the exhaust ports.

 

[Troutfrea]

Thank you for that explanation. I know that can be an issue so I always try to let my sleds warm up to operating temperature before taking off on them. The only instance when that wouldn't be true is if the sled sat while we took a break and then my daughter took off without letting it warm back up. However, my thought is there would be enough residual heat in the motor to prevent a seizure as you've described. I have not taken the y-pipe but that's a good idea. If I do, I will report back with what I find.