08-22-2011, 07:31 AM #1
- Join Date
- May 2009
- Broadstairs, Kent, England
Another discussion on the rear exhaust valves
Apologies for starting another thread on the early problematic rear exhaust valves, but I have some specific questions that I think are worthy of debate and increased awareness.... For those of you who have been regular readers you'll know I'm currently repairing my second exhaust valve failure on my '04 RXP!
Popular opinion on this forum is that the pre '06 rear cylinder exhaust valves are prone to failure. Most people recommend replacing the valves on these earlier skis with aftermarket Ferrea ones. Opinion is that the earlier valves were hollow and therefore weaker and the later or after market ones are not (and therefore stronger). But I'm not sure the valve strength is the problem, I think it's the valves ability to not rust. what I mean is that I think what causes the catostophic engine failure is the valve sticking open and hitting the piston, not the valve end just snapping. This seems to be the case on my latest ski, the broken exhaust valve stems are corroded, the exhaust valve I took out from the middle cylinder looks fine, apart from some carbon build up. What do you guys and girls think? Is it it the valve stems corroding that is the cause of the problem? If so why are the later valves better, do they have corrosion resistant material?
Secondly, if my theory above is right, why is it always the rear cylinder that goes? Other threads here suggest it's mositure from the water box that causes the corrosion, but surely the condensation would settle in all cylinders? I agree fogging by pulling the injectors after every ride is a sensible precaution by the way.
Like I say, sorry for starting another thread, but It would be good to get every one on the same page on why these valves really fail.
Cheers.... Adrian (hoping for my recondition block and head back in a few days)!
08-22-2011, 06:02 PM #2
- Join Date
- Sep 2009
Well, this topic has been beaten to death recently, so I will keep this short. First of all, both old and new valves are hollow. The early ones were made from an alloy that rusts easily, and is brittle. The new one's are Inconel, which is almost as corrosion resistant as stainless, and it is tough versus brittle.
The valves don't break from sticking, they break from corrosion induced cracking at the weld junction. (Heads and stems are made from different materials and are spun welded together )
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