The original poster was Vitaliy. (And it doesn't bother me as long as good info gets back to Vitaliy). :) I concur with what's said below. One of the possible valve stem failures causes if stress reversal fatigue. In general there needs to be stress reversal (back and forth between tension and compression). One of the stress reversals is due to loose valve guides (could either be valve stem undersize, or valve guide bore oversize). With the valve stem cocked to one side, the valve head hits the seat on one side. If the stem wobbles to the other side (possible since the bore is loose), the head strikes on the opposite side and where there was bending tension first, there now is bending compression. At a few thousand RPM, it doesn't take long for fatigue failure to take place. Probably the valve guide clearance should be checked. The valve stem can also stretch if high RPM's are used. The stem diameter can be reduced due to either/both erosion/corrosion and stretch. Valve stem/guide wear can also occur with wrong fuels. When unleaded fuels became common, some engines had valve guide issues. One can buy a lead (or look alike) additive for the gasoline, added to the tank each fill up, commonly used on 50's and earlier engines. On many (most) piston aircraft engines, it is required to replace the exhaust valves at overhaul which for revenue service is required usually between 1400 - 2000 hours of use (flight). The water in the cylinder, as said below, also could have been a long term (maybe not that long) leaky head gasket as I noted previously by the gasket surface color. Does this unit have a sealed cooling system, or circulate sea water? If sealed, this type leak in a car is usually noticed by loss of coolant, but no external leaks. The complaint is having to add coolant, of the less than good maintenance driver, suddenly overheats the engine, usually warping the cylinder head. Richard Prosser wrote: > Woops, > Sorry, I'm not sure who the original poser is, but its not Carl. > RP > > 2008/8/19 Richard Prosser : > >> Carl, >> >> I really can't figure out how an engine "going hydraulic" would do >> that sort of damage. It looks to me more likely that >> >> a) The valvestem broke, probably a fatigue failure. >> b) The valvehead rattled around the combustion chamber for a while, >> damaging the top of the piston, the head & the spark plug and possibly >> other valves. >> c) At some stage the valvehead got sufficiently jammed to stop the >> motor and posiibly displaced the head enough to allow water in through >> the head gasket. (IIRC there was water in the cylinder when the head >> was removed. It could have seeped in later anyway from the >> waterjacket. >> >> See if you can get a closeup photo of the break in the vavestem. >> Fatigue breaks are quite characteristic and if that's the root cause, >> you're off the hook. What you would be looking for is a series of arcs >> across the surface of the broken metal caused by crack progression. >> I'm sure there's some photos on the web somewhere >> (http://en.wikipedia.org/wiki/Metal_fatigue shows an aluminum piece >> with fatigue crack growth). >> >> Just an opinion of course!. >> >> RP >> >> 2008/8/19 Stephen D. Barnes : >> >>> Vitaliy wrote: >>> >>>> Hi All, >>>> >>>> This is a continuation of the [EE] thread with the same subject. >>>> >>>> Carl Denk said: >>>> >>>> >>>>> Pictures would be worth a 1000 words. :) >>>>> >>>>> >>>> http://www.maksimov.org/jetski/ >>>> >>>> Would love to hear your thoughts! >>>> >>>> Sincerely, >>>> >>>> Vitaliy >>>> >>>> >>>> >>>> >>> Dude, that is one kick a$# jet ski motor! ;-) >>> >>> -- >>> Regards, >>> Stephen D. Barnes >>> >>> -- >>> http://www.piclist.com PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist >>> >>> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist