piclist 2008\08\18\172338a >
Thread: Jet ski -- possible ways for the water to get inthe engine?
face BY : Carl Denk email (remove spam text)

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:
{Quote hidden}

<48A9E846.2020409@alltel.net> 7bit

In reply to: <d02e69350808181332w32a0319bo8a4268e0e040cf28@mail.gmail.com>
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