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- Aug 18, 2008
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I am looking for advice regarding a leak in my crankcase, which I am hoping will not require a complete tear down to patch.
After I had the engine and gearbox professionally rebuilt a few years ago my bike’s motor was beautifully oil tight. I have only done a few thousand miles on it since, but it has now developed a very significant leak – as well as the annoying ones like from the tappet covers and the spindle plates (spindles fixed with new gaskets; I will do the tappets soon).
At first I thought that I must be dropping a lot of oil out of the overflow from the oil tank into the airbox; so recently I connected a drain pipe to the oil tank overflow which I run to a catch bottle mounted on the Z plate. That appears to work fine, and there is very little oil in the catch bottle.
The leak remains, and has got worse. After a ride the underside of the engine and gearbox is covered in oil; as is the centre stand, and even the rear wheel and tire. Oil drips from each low point of the motor and gearbox. It does not inspire me with confidence to know that I am riding through my own self created oil slick. When I stop after a ride within seconds the ground is covered with about 10 decent size drips of oil, and the side of the back tyre – especially the right hand side - and wheel is slick with oil (presumably oil is under the tread too, but the pavement wipes it off).
I have spent some time trying to identify the source. At first I thought it might be the gearbox; and that remains a possibility; certainly the underside of the gearbox is covered in oil when I stop, and I found that the breather hole in the gearbox inspection cover was blocked; I have opened it up again with a thin wire; I have been checking the oil level and it does not seem to be reducing markedly.
I have also checked the sump plug; I have recently fitted a new copper washer which I coated liberally with gasket goo; and have tightened it when the motor is warm. There could be a leak from here, but that does not account for all of the oil on the underside of the motor in front of the sump plug.
I think that the real fault is a leak at the front of the crankcase, where the head connects to the crankcase, right above the front isolastic. I have attached a photo. I have run the motor and seen oil leaking out from here. I don’t know if it is visible but at some point the crankcase has been damaged and rebuilt at this point; you can see that additional aluminium has been put here on the right hand side of the crankcase (the right being viewed from front on in the photo; if you were sitting on the bike it would be the left hand side of the crank case). The oil seems to be exiting the crankcase mostly from the horizontal join between the crankcase and the cylinder head, but is also leaking from the vertical join between the two crankcase halves; for about a centimetre down from the cylinder head. It then runs down under the motor; and I assume is then blown onto the gearbox and under the bike.
Some oil leaks might just be a fact of life with these old bikes, but I don’t think that this one is acceptable; especially given the amount of oil that seems to be flowing down from the leak, under the bike, and being thrown all over the back wheel and tyre. It doesn’t feel safe (but I have not lost traction as yet), and I’m not sure that it would pass a warrant with that much oil on it after even a short ride.
So the question that I have is – how to fix it? I am scared that I have to take out the motor, and completely disassemble it (or probably get someone else to do that; I have yet to go take apart the motor) and regasket and fix it, and maybe have the crankcase surfaces ground down, or built up; or at worst replace the side of the crank case that has been repaired (and that is the one with the engine number – matching; I would like to avoid that if possible).
That seems to be a really extreme step to take for a motor that is otherwise running beautifully and has only been recently (in mileage) fully rebuilt. And super expensive given that I think that a complete strip down and rebuild is beyond my skills.
Is there an alternative? Any sort of external gasket goo?
Will better crankcase breathing assist a leak in this position?
This is a 1970, with the timed breather. I can’t fit Jim Comstock’s sump plug breather because of the brace in the 1970 frame. I have purchased a reed valve (the aftermarket Yamaha one) that I had intended to install onto the timing case blanking plate; but have not done so yet.
This is partly because I am unsure of how effective such a breather would be attached to the timing case as opposed to the crankcase proper, and Jim’s suggestions that the oil holes might need drilling in different positions, so that the oil level is not too high and the oil not too churned by the effect of the breather – again only possible with a complete strip down.
Having read all that I could on that subject I do think that it probably was worth connecting the reed valve notwithstanding that it is not a complete solution, and leaving the timed breather in place on the other side of the crankcase – surely both working together will be better than just one - even if neither is as good as a proper Comstock breather?
My first attempt came unstuck a while ago when I attempted to take off the blanking plate. I found that I could not unscrew it. The two top screws came out easily, but the bottom one just turns; I think that this one is a bolt and nut rather than a screw that attaches to the a thread in the crankcase (that seems to be the situation according to the Andover Norton exploded motor diagram – but their diagram has the nut on the outside; mine looks like an identical screw on the outside; it must have a nut on the inside.) At the time I did not want to use force and wreck the gasket, and risk having a nut drop into the timing case, and I had not discovered the extent of the leak then, but I will probably go through the exercise now.
So – what to do?
Although I am seeking advice and input I suspect that there is a limit of the advice that people can give – it will be a matter of seeing what works. In my own mind I am now committed to trying the reed valve breather to see if that relieves pressure and helps. I intend to leave the existing timed breather in place as well upon the assumption that the reed breather from the timing case without new holes drilled between the crankcase and timing case will not be fully effective on its own.
Is anyone aware of is some sort of external goo or high tech duct tape that can be applied to the leak itself? Any other sort of process to attempt to repair this short of a complete motor strip down, removing the head and splitting the cases, so that the faces of the join can be examined and built up or ground down, and new gaskets put in place?
After I had the engine and gearbox professionally rebuilt a few years ago my bike’s motor was beautifully oil tight. I have only done a few thousand miles on it since, but it has now developed a very significant leak – as well as the annoying ones like from the tappet covers and the spindle plates (spindles fixed with new gaskets; I will do the tappets soon).
At first I thought that I must be dropping a lot of oil out of the overflow from the oil tank into the airbox; so recently I connected a drain pipe to the oil tank overflow which I run to a catch bottle mounted on the Z plate. That appears to work fine, and there is very little oil in the catch bottle.
The leak remains, and has got worse. After a ride the underside of the engine and gearbox is covered in oil; as is the centre stand, and even the rear wheel and tire. Oil drips from each low point of the motor and gearbox. It does not inspire me with confidence to know that I am riding through my own self created oil slick. When I stop after a ride within seconds the ground is covered with about 10 decent size drips of oil, and the side of the back tyre – especially the right hand side - and wheel is slick with oil (presumably oil is under the tread too, but the pavement wipes it off).
I have spent some time trying to identify the source. At first I thought it might be the gearbox; and that remains a possibility; certainly the underside of the gearbox is covered in oil when I stop, and I found that the breather hole in the gearbox inspection cover was blocked; I have opened it up again with a thin wire; I have been checking the oil level and it does not seem to be reducing markedly.
I have also checked the sump plug; I have recently fitted a new copper washer which I coated liberally with gasket goo; and have tightened it when the motor is warm. There could be a leak from here, but that does not account for all of the oil on the underside of the motor in front of the sump plug.
I think that the real fault is a leak at the front of the crankcase, where the head connects to the crankcase, right above the front isolastic. I have attached a photo. I have run the motor and seen oil leaking out from here. I don’t know if it is visible but at some point the crankcase has been damaged and rebuilt at this point; you can see that additional aluminium has been put here on the right hand side of the crankcase (the right being viewed from front on in the photo; if you were sitting on the bike it would be the left hand side of the crank case). The oil seems to be exiting the crankcase mostly from the horizontal join between the crankcase and the cylinder head, but is also leaking from the vertical join between the two crankcase halves; for about a centimetre down from the cylinder head. It then runs down under the motor; and I assume is then blown onto the gearbox and under the bike.
Some oil leaks might just be a fact of life with these old bikes, but I don’t think that this one is acceptable; especially given the amount of oil that seems to be flowing down from the leak, under the bike, and being thrown all over the back wheel and tyre. It doesn’t feel safe (but I have not lost traction as yet), and I’m not sure that it would pass a warrant with that much oil on it after even a short ride.
So the question that I have is – how to fix it? I am scared that I have to take out the motor, and completely disassemble it (or probably get someone else to do that; I have yet to go take apart the motor) and regasket and fix it, and maybe have the crankcase surfaces ground down, or built up; or at worst replace the side of the crank case that has been repaired (and that is the one with the engine number – matching; I would like to avoid that if possible).
That seems to be a really extreme step to take for a motor that is otherwise running beautifully and has only been recently (in mileage) fully rebuilt. And super expensive given that I think that a complete strip down and rebuild is beyond my skills.
Is there an alternative? Any sort of external gasket goo?
Will better crankcase breathing assist a leak in this position?
This is a 1970, with the timed breather. I can’t fit Jim Comstock’s sump plug breather because of the brace in the 1970 frame. I have purchased a reed valve (the aftermarket Yamaha one) that I had intended to install onto the timing case blanking plate; but have not done so yet.
This is partly because I am unsure of how effective such a breather would be attached to the timing case as opposed to the crankcase proper, and Jim’s suggestions that the oil holes might need drilling in different positions, so that the oil level is not too high and the oil not too churned by the effect of the breather – again only possible with a complete strip down.
Having read all that I could on that subject I do think that it probably was worth connecting the reed valve notwithstanding that it is not a complete solution, and leaving the timed breather in place on the other side of the crankcase – surely both working together will be better than just one - even if neither is as good as a proper Comstock breather?
My first attempt came unstuck a while ago when I attempted to take off the blanking plate. I found that I could not unscrew it. The two top screws came out easily, but the bottom one just turns; I think that this one is a bolt and nut rather than a screw that attaches to the a thread in the crankcase (that seems to be the situation according to the Andover Norton exploded motor diagram – but their diagram has the nut on the outside; mine looks like an identical screw on the outside; it must have a nut on the inside.) At the time I did not want to use force and wreck the gasket, and risk having a nut drop into the timing case, and I had not discovered the extent of the leak then, but I will probably go through the exercise now.
So – what to do?
Although I am seeking advice and input I suspect that there is a limit of the advice that people can give – it will be a matter of seeing what works. In my own mind I am now committed to trying the reed valve breather to see if that relieves pressure and helps. I intend to leave the existing timed breather in place as well upon the assumption that the reed breather from the timing case without new holes drilled between the crankcase and timing case will not be fully effective on its own.
Is anyone aware of is some sort of external goo or high tech duct tape that can be applied to the leak itself? Any other sort of process to attempt to repair this short of a complete motor strip down, removing the head and splitting the cases, so that the faces of the join can be examined and built up or ground down, and new gaskets put in place?