clocker Posted November 4, 2010 Share Posted November 4, 2010 Hi all. This bike is a 1992 YZ80D and it blows crank case oil out of a bypass hose when it's under load. Anyone hazard a guess as to what the fix might be before I start taking things apart? I've never had one of these apart, but will have to shortly if my daughter wants to keep riding this thing. I have an owners service manual, but it lacks a diagram that might reveal how pressure is building in the crank case under load to blow out oil. It's getting worse so I'll have to do something about it this winter to have it ready for spring. Any insight people here might have to offer would be welcome. Ian Edit - Crank case... not crack.. save me! Link to comment Share on other sites More sharing options...
bob-c Posted December 6, 2010 Share Posted December 6, 2010 Hi all. This bike is a 1992 YZ80D and it blows crank case oil out of a bypass hose when it's under load. Anyone hazard a guess as to what the fix might be before I start taking things apart? I've never had one of these apart, but will have to shortly if my daughter wants to keep riding this thing. I have an owners service manual, but it lacks a diagram that might reveal how pressure is building in the crank case under load to blow out oil. It's getting worse so I'll have to do something about it this winter to have it ready for spring. Any insight people here might have to offer would be welcome. Ian Edit - Crank case... not crack.. save me! Check oil level , if not overfilled then it is likely to be a worn crankshaft seal , you may as well do both sides . OEM Yamaha ones are expensive but better than pattern ones. Bob Link to comment Share on other sites More sharing options...
clocker Posted December 6, 2010 Author Share Posted December 6, 2010 Check oil level , if not overfilled then it is likely to be a worn crankshaft seal , you may as well do both sides . OEM Yamaha ones are expensive but better than pattern ones. Bob Thanks Bob. Got it on the oil level. Link to comment Share on other sites More sharing options...
blackhat250 Posted December 6, 2010 Share Posted December 6, 2010 Hi clocker" the piston rings must be worn also "crankcase pressure" is caused by blow-pass [ compression] down side of rings, better inspect while stripped, rebore might be on the cards, measure at skirt of barrel. [you need sizes from workshop manual] ,,, Link to comment Share on other sites More sharing options...
clocker Posted December 6, 2010 Author Share Posted December 6, 2010 Hi clocker" the piston rings must be worn also "crankcase pressure" is caused by blow-pass [ compression] down side of rings, better inspect while stripped, rebore might be on the cards, measure at skirt of barrel. [you need sizes from workshop manual] ,,, As I understand it the two chambers have no connection, but if they do and it continues to spew cankcase oil I'll be sure to check the rings and bore, thanks. Link to comment Share on other sites More sharing options...
blackhat250 Posted December 6, 2010 Share Posted December 6, 2010 As I understand it the two chambers have no connection, but if they do and it continues to spew cankcase oil I'll be sure to check the rings and bore, thanks. Ah" its a little two-stroke " Link to comment Share on other sites More sharing options...
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