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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Migration of oil
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<blockquote data-quote="timetraveller" data-source="post: 52905" data-attributes="member: 456"><p>O.K. Well here is one scenario but I hope that I am wrong (it would not be the first time). A leak has developed between the two crankcase halves or the castings have become porous. This would have to be at the front of the gearbox. If the leak, which must be very slow, is at a low level then oil is going from the gearbox into the catchment volume behind the flywheels where oil is flung by the flywheels before being sucked into the return side of the pump. This would then become part of the general engine oil circulation. The discolouration of the gearbox oil would then have to be caused by some of the engine oil which is left in that catchment leaking back when the engine is stationary. In principle the catchment should be empty but perhaps never completely. If the leak is above that level then it almost certainly has to be not much higher as not much further up there is the tunnel which is there to take a left hand kick starter. Oil at that level would probably find some other way out rather than go through two sealed faces and into the engine part of the crankcase. If the leak was above that tunnel then it could only mean that oil splash is getting at the leak, not the stationary oil when everything is just sitting there. A higher leak would also make it difficult for engine oil to get back into the gearbox to cause the discolouration. I can think of a test but it would be a pain to do. Remove the end plug from the oil pump and then rotate the engine so that the oil pump plunger is leaving the passage way from the catchment to the pump open. Then put lots of clean oil into the gearbox and wait to see if it starts to leak out of the rear of the oil pump. You might be able to speed up the test by applying a small amount of excess air pressure into the gearbox via the filler hole. If oil does start to show up then you know you have a leak and at what level. Unfortunately if it does not leak through that might just mean that the leak is only there when the engine is hot. Its a new one on me but there are people in the Club who have worked on far more engines than me so perhaps they can help out. If it turns out to be none of the above then we are all going to learn something new about Vins. Good luck.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 52905, member: 456"] O.K. Well here is one scenario but I hope that I am wrong (it would not be the first time). A leak has developed between the two crankcase halves or the castings have become porous. This would have to be at the front of the gearbox. If the leak, which must be very slow, is at a low level then oil is going from the gearbox into the catchment volume behind the flywheels where oil is flung by the flywheels before being sucked into the return side of the pump. This would then become part of the general engine oil circulation. The discolouration of the gearbox oil would then have to be caused by some of the engine oil which is left in that catchment leaking back when the engine is stationary. In principle the catchment should be empty but perhaps never completely. If the leak is above that level then it almost certainly has to be not much higher as not much further up there is the tunnel which is there to take a left hand kick starter. Oil at that level would probably find some other way out rather than go through two sealed faces and into the engine part of the crankcase. If the leak was above that tunnel then it could only mean that oil splash is getting at the leak, not the stationary oil when everything is just sitting there. A higher leak would also make it difficult for engine oil to get back into the gearbox to cause the discolouration. I can think of a test but it would be a pain to do. Remove the end plug from the oil pump and then rotate the engine so that the oil pump plunger is leaving the passage way from the catchment to the pump open. Then put lots of clean oil into the gearbox and wait to see if it starts to leak out of the rear of the oil pump. You might be able to speed up the test by applying a small amount of excess air pressure into the gearbox via the filler hole. If oil does start to show up then you know you have a leak and at what level. Unfortunately if it does not leak through that might just mean that the leak is only there when the engine is hot. Its a new one on me but there are people in the Club who have worked on far more engines than me so perhaps they can help out. If it turns out to be none of the above then we are all going to learn something new about Vins. Good luck. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Migration of oil
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