View Full Version : YSM12 runaway

08-17-2009, 12:29 AM
"I have a YSM12, vintage around 1982, recently rebuilt after it ranaway and ended up with salt water in the crankcase. Since the rebuild, we are having the same problem - the engine revs and won't quit unless decompressed. There is a stream of oil coming from the air intake tube, as if there is too much oil pressure in the crankcase and no relief for it except to go through the blow-by tube. I see in the manual that there is an oil pressure regulator valve - could this be the culprit? Second, if so, how do I get one. The guys that rebuilt the engine claim the part is no longer available. Thanks for any advice!"

10-14-2009, 06:44 PM
"Hi Richard,
This valve is a waffer thin metal and is opposite the piston and head side. It is the cover place to the engine crank case. Removed you can see the big end of the conrod. What happens is it is put back upside down and therefore oil will feed into and by pass and valve and go into the engine intake via the hose Get your self a workshop manual
Get a picture of this part, the valve should sit on the top end of the cover. The hose travels down then up to the intake pipe. Also sailing and with the engine running and the vessel underway, the yaw of the vessel will cause lub oil into and past the waffer valve and hose and cause run away. Water in the base was prolly caused by a failed head gasket or exhaust elbow failure.
Take Care, Ron"

10-15-2009, 01:11 AM
Thanks. The manual I have does not reference this valve at all,though it is the shop manual for this engine.

Rich Borton"