I just had my engine rebuilt at a cost of $1650. The cases were split, new Superblend bearings, Black Diamond valves, rings etc. The main reason I had it rebuilt was the leaking through the case halves at various locations especially right behind the cylinders on the top. You could actually see the oil weeping through while it was running. Now that the job is done and oil is in the machine, I don't see any leaks on the floor under the engine. Being a machine that was built in 1970, I would imagine that over 45 years, the compound in between the case halves has gone hard and fallen out. As there is no gasket in between this is what happens. The only solution in my opinion is to split the halves and while they are apart, do anything that needs to be done and then apply new modern compound reassemble and move on to the next leak !
Any suggestions for fixing a crankcase leak?
- Thread starter Chris T
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Motoseal. Crankcase breather. :wink:
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Guys, thanks for all of your input. It has been a long time; for various reasons I have been away from my bike most of the year.
Touch wood, I may have now diagnosed the problem and resolved it. Well actually 1up2down diagnosed it. What had happened is that when I installed the hose from the oil tank to a catch bottle - as opposed to just letting the oil tank breath into the air filter as standard - I had bought a fairly flexible lightweight hose; which was all that Supercheap Auto had on the shelf at the time. As the motor ran the hose kinked - inside the air filter cover where it was not visible; which blocked it off, and allowed (presumably) massive pressure to build up in the crankcase; and oil found its way out from whereever it could. The fix was simple; I bought better quality hose and replaced it.
I took the bike out for a ride yesterday. Before I did so, I did one other thing that I have never done before - drain the crankcase and put all of the oil back into the oil tank - which must have been pretty much all the oil in the bike after it had sat for 8 months or so. After about an hour's ride on country roads the bike sat in the garage and over the next hour about 3 drips of oil hit the garage floor; not perfect, but a huge improvement on the stream of oil that was coming out before. There was no leak from the join at the front of the crankcase.
I don't know exactly where the relatively small quantity of oil is coming from; it could be from the crankcase, the gearbox, or the primary; or all three; I will have to keep diagnosing; and probably need to use a mirror; I don't have a lift. I do know that a little came out of the swingarm cradle.
There was a drip of oil on the sump plug; so an easy conclusion is that some is leaking out of that; but I suspect that it is not; I have a relatively new copper washer on the sump plug; and put gasket goo on it; the sump plug is the lowest point of the motor so that is where the oil will drain to; especially when it is pushed by the movement of air while riding. So now I have an annoying issue; as opposed to a disaster.
The hose from the oil tank to the catch bottle did work as intended. And I am pretty much resigned to having to drain the crankcase every time I leave the bike for more than a few days. The increase in crankcase pressure as a result of the large volume of oil that seeks into it must be very significant.
I can certainly see the attraction of putting a valve in the line to stop wetsumping; but I know that solution is not for me; given the number of times I have stopped the bike; turned off the petcocks, then started again without remembering to turn on the petcocks, I know that any wetsumping valve system that was not fully automated (like being linked to the main ignition system) would be fatal for me.
One other possible benefit of draining the crank case. Normally after the bike has sat for some time it can take a good few kicks over several minutes to get it running. This time it started on the third kick. I am wondering if taking all that oil out of the crankcase allowed the crank case to spin faster on the kick; so that it was easier to start.
Touch wood, I may have now diagnosed the problem and resolved it. Well actually 1up2down diagnosed it. What had happened is that when I installed the hose from the oil tank to a catch bottle - as opposed to just letting the oil tank breath into the air filter as standard - I had bought a fairly flexible lightweight hose; which was all that Supercheap Auto had on the shelf at the time. As the motor ran the hose kinked - inside the air filter cover where it was not visible; which blocked it off, and allowed (presumably) massive pressure to build up in the crankcase; and oil found its way out from whereever it could. The fix was simple; I bought better quality hose and replaced it.
I took the bike out for a ride yesterday. Before I did so, I did one other thing that I have never done before - drain the crankcase and put all of the oil back into the oil tank - which must have been pretty much all the oil in the bike after it had sat for 8 months or so. After about an hour's ride on country roads the bike sat in the garage and over the next hour about 3 drips of oil hit the garage floor; not perfect, but a huge improvement on the stream of oil that was coming out before. There was no leak from the join at the front of the crankcase.
I don't know exactly where the relatively small quantity of oil is coming from; it could be from the crankcase, the gearbox, or the primary; or all three; I will have to keep diagnosing; and probably need to use a mirror; I don't have a lift. I do know that a little came out of the swingarm cradle.
There was a drip of oil on the sump plug; so an easy conclusion is that some is leaking out of that; but I suspect that it is not; I have a relatively new copper washer on the sump plug; and put gasket goo on it; the sump plug is the lowest point of the motor so that is where the oil will drain to; especially when it is pushed by the movement of air while riding. So now I have an annoying issue; as opposed to a disaster.
The hose from the oil tank to the catch bottle did work as intended. And I am pretty much resigned to having to drain the crankcase every time I leave the bike for more than a few days. The increase in crankcase pressure as a result of the large volume of oil that seeks into it must be very significant.
I can certainly see the attraction of putting a valve in the line to stop wetsumping; but I know that solution is not for me; given the number of times I have stopped the bike; turned off the petcocks, then started again without remembering to turn on the petcocks, I know that any wetsumping valve system that was not fully automated (like being linked to the main ignition system) would be fatal for me.
One other possible benefit of draining the crank case. Normally after the bike has sat for some time it can take a good few kicks over several minutes to get it running. This time it started on the third kick. I am wondering if taking all that oil out of the crankcase allowed the crank case to spin faster on the kick; so that it was easier to start.
Hi Chris
It's good to hear that you solved the problem.
As the owner of a 70 model with welded crankcases, my story may interest you.
I bought the bike as a basket case in 1983. Amongst a lot of problems I faced, the crankcases were in 5 pieces. I had never restored a motor cycle before, but I saw it as a test of my skills as an amateur mechanic.
Local bike shop owner Brian Clarkson knew a very good welder named Kiwi. He did the job well. I had to re-drill the oil drain to the timing case as one of the welds went through that hole. The barrel face of the cases was good, but I noticed a large gap between the halves at the top rear. I fixed it by aralditing a thin piece of aluminium there and filing it to blend in. Don't laugh, the only oil leak on the bike ended up being a slight weep from the kickstart, which I fixed by fitting a thicker "o" ring (metric 25 x 4 mm). I didn't use any sealing compound anywhere on the bike, except of course between the crankcase halves. I never gave much thought to engine breathing at the time, although the small size of the timed breather ports seemed strange.
I used the bike regularly for some years but then it languished for a lot of years until in 2010 I decided to celebrate its 40th birthday by using it again.
But it punished me for neglecting it by refusing to run. So I stripped it right down again to do the job on a better budget this time. That was when I discovered this forum and got to thinking about those small breather holes.
In the end I chose to do the timing case breather mod, but not to route the outlet to the oil tank. I just don't like the idea of having the engine breathing into its oil unless it's necessary, and it didn't seem necessary with timing case breathing. It breathes through an XS 650 reed valve and then into a home made catch tank which nestles into the plates between engine and gearbox.
That allowed me to use the original engine breather port on the oil tank as a vent to atmosphere, and to plug the tube that lets oil drip into the air filter.
So far, albeit with only low miles on this setup, there has been no oil in the catch tank.
Cheers
Martin
It's good to hear that you solved the problem.
As the owner of a 70 model with welded crankcases, my story may interest you.
I bought the bike as a basket case in 1983. Amongst a lot of problems I faced, the crankcases were in 5 pieces. I had never restored a motor cycle before, but I saw it as a test of my skills as an amateur mechanic.
Local bike shop owner Brian Clarkson knew a very good welder named Kiwi. He did the job well. I had to re-drill the oil drain to the timing case as one of the welds went through that hole. The barrel face of the cases was good, but I noticed a large gap between the halves at the top rear. I fixed it by aralditing a thin piece of aluminium there and filing it to blend in. Don't laugh, the only oil leak on the bike ended up being a slight weep from the kickstart, which I fixed by fitting a thicker "o" ring (metric 25 x 4 mm). I didn't use any sealing compound anywhere on the bike, except of course between the crankcase halves. I never gave much thought to engine breathing at the time, although the small size of the timed breather ports seemed strange.
I used the bike regularly for some years but then it languished for a lot of years until in 2010 I decided to celebrate its 40th birthday by using it again.
But it punished me for neglecting it by refusing to run. So I stripped it right down again to do the job on a better budget this time. That was when I discovered this forum and got to thinking about those small breather holes.
In the end I chose to do the timing case breather mod, but not to route the outlet to the oil tank. I just don't like the idea of having the engine breathing into its oil unless it's necessary, and it didn't seem necessary with timing case breathing. It breathes through an XS 650 reed valve and then into a home made catch tank which nestles into the plates between engine and gearbox.
That allowed me to use the original engine breather port on the oil tank as a vent to atmosphere, and to plug the tube that lets oil drip into the air filter.
So far, albeit with only low miles on this setup, there has been no oil in the catch tank.
Cheers
Martin
o0norton0o
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Early model commandos with the timed breather on the end of the camshaft need a breather modification. I own a '70 commando and it always had minor leaks until I modified the timing chest and added a reed breather.
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