Randum loose of compretion

"We have a yanmar YSM12 diesel

"We have a yanmar YSM12 diesel in a 1979 hunter 30 (in very, very good shape and well taken care of) we just bought. While moveing it home to NC form Va on the ICW we expernced randum loose of comprretion whish resulted in the engine stoping. after 15 to 20 min of hand cranking and pushing on the decompretion valve it would regain compretion and start. the engine would run four to six hrs with out a problem and then repeat the same problem. Other than that it runs very well. Is the decompretion value or a sticking exhust value the problem? What to Do?"

"if you suspect a sticking val

"if you suspect a sticking valve, remove the cover. (very easy, just one bolt) it will drip a small amount of oil, so put a rag, or oil-sorb below to catch. you can check valve adjustment, springs, and pushrods. loose valve suggests sticking. tight valve may be mushroomed. pulling head not too difficult if needed. make sure you plug exhaust before removing! water can siphon in, and sink your boat. also be carefull overcranking. once waterlift fills, water can fill engine. shut off water intake after 30 seconds with no start. (don,t forget to turn back on once started)"