YSB12 Head Overhaul - valve seals??

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Henry Weber

Does anyone know if the Yanmar YSB12 (1977) in my H30 uses valve seals on the valve stems of the head. Am in the process of overhauling engine. Took head to machine shop to have new valves and guides installed. Mechanic insists that he needs to install seals on the valve stems. However, both the Yanmar parts book and service manual do not show any seals. If anyone can shed light on this I would appreciate it. It seems to run fine without seals but if they should be there I want to install them. Thanks a lot, Henry Weber
 
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Gordon Torresen

Valve seals

Not all engines have umbrellas on the valve stems. Yours is one that doesn't. The valve stem seals are less critical on a diesel because there is less vacuum within the manifold as compared to gasoline engines. Your mechanic should be commended for looking after your interests.
 
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john renfro

seal

i know little about diesel engins, but the umbrella type seals on a gas engin work like majic. if you replace them you can go from spark plugs fouling every two weeks, to not fouling once in three years. john
 
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Henry Weber

YSB12 valve seals

Thanks Gordon and John for the quick answer. Henry
 
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