Hello everyone, I have recently cleaned off 20+ years of cobwebs from a 1969 mk3D. After some electrical trouble shooting, fresh oil,carb rebiuld, and my first desmo valve adjustment it is running well. I thought I was ready to do some riding and then I noticed the oil leak coming from behind the countershaft sprocket. It is leaking bad enough to start oiling down the rear tire after a few miles of riding. So far I have re-tourqued the sprocket nut(no improvement),then I took off the sprocket cleaned it and the shaft and used rtv silicoln to seal the sprocket to the shaft and the inner bearing race that it must seal against. It still leaks as bad as ever. All I can figure now is that the oil is leaking thru the sealed bearing or between the outer race and the case.
Does anyone have any experience with this problem? What can I do now?
thanks for any suggestions, Mark
350 D oil leak help
The bearing behind the C/S sprocket is a 1-sided sealed type with the seal (obviously) up against the case. Depending on what's in there, its either a rubber seal or a metal plate that clips into grooves in the bearing races. These seals don't really fail the way a conventional rubber oil seal fails. Nor do they seal as well, especially the metal plate type. Also, this bearing is only oiled by "splash". There is no pressure feed to the transmission shafts. A lot of oil passing through this bearing would indicate that the crankcase vent may be plugged or the engine is over-filled with oil (although both of these situations would make the engine run poorly). Also, the countershaft sprocket is threaded on the end where it slips into the case. The idea is that the threads screw any oil that passes the bearing back into the bearing cavity. I believe there is a drain hole or notch in the bottom of the beaing bore to drain oil that passes the bearing (another possible source of oil if the drain is plugged ). The bore in the case that this threaded spigot on the sprocket fits into must be a pretty tight fit. If the bore in the case has been gouged or damaged such that the threads aren't a tight fit, oil will pass through more readily.
Thanks for the good info. I have changed the oil and and refilled with the proper amount. I have also checked the breather. you can feel a lot of air movement so it isn't stopped up. I was wondering if the engine might have so much blowby that it is just presurizing the crankcase and forcing the oil out,but it seems to have good compression and runs strong. I am not sure what to try next, but if/when I get the bleeding stopped I will post the solution. thanks, Mark