Any suggestions for fixing a crankcase leak?

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?

it is possible that you have inadvertently installed a closed instead of an open motor breathing loop

if I am interpreting you correctly, you are labeling the oil tank "breather" as an "overflow", which it is not

the motor breathes into the larger diameter hose coming from the motor and going up and into the oil tank

on the top of the oil tank is a smaller metal tube that facing forward, this has a smaller piece or hose on it that it designed to breathe
into "air", as in no restriction

Norton commonly routed this oil tank breather down and into the air filter, but note that this still allowed an open loop

I am suggesting that IF you have connected that oil tank breather to say a bottle and the bottle itself then does not have a hole
cut in it near the top for the air, which is under pressure, to exit into the atmosphere then you a closed loop system, and in such
a set up with no sufficient venting the motor can be strangling and oil is then forced to find some way out, of any seams

years ago I made the mistake of putting the oil tank top breather tube into a plastic bottle in the front of the battery box, it fit nice and tight around the hose, and when I came back from a short ride oil was puking out from everywhere around the motor

I cut a small piece out of the bottle which allowed the air to vent and no more oil leaks

is it possible you have such a closed loop system in place with your "overflow" bottle? just a thought

thanks for the suggestion. It is possible that the airpipe into the bottle is blocked; it is just a little plastic bottle with no lid; so plenty of room for air to escape, but the pipe into it is at the bottle of the so might be sitting on the bottom and restricting airflow. And it is also possible that the pipe has kinked at joint into the oil tank; it had done this previously, and I attempted to fix it by putting a larger piece of hose around it to hold it in position. I think I should check that.

The part you say is leaking is the joint between the crankcase and the barrel, the cylinder head is the bit on top of the barrel. There appears to have been a welded repair to the front LH crankcase half. this will nearly always result in some distortion leading to leaks. You may be able to reduce the leaks by improving the breathing and the Yamaha reed valve would be a good place to start. Fitting it in the back of the timing cover is a good place for it but as you have guessed, there is a nut inside the timing cover. Taking the timing cover off will require the timing being reset. Without stripping the crankcases down you will not know the extent of the fettling required to fix the crankcase leak. Probably not what you wanted to hear.

Ta.

Chris,

I agree with Gripper it looks like there is a repair on the crankcase right were you are describing the leak. Could you post a higher resolution photo?

The one you posted is pretty small.

Dennis

To ID the various leaks best way is power wash then run a few 100 yd then shut down and peer around, in cycles till found. Helps if oil darkened otherwise some put on talc powder to help. Likely no permanent fix until area around the seam repair is blacksmith hammered closer to compensate for weld repair contracture then resealed with natural fiber thread & gap filling vibration absorbing non hardening sealant. In mean time if was mine I'd work off the iso mount then spray with an external sealant then spritz with semi silver alu tone paint and fly with the wind til leaks too much again or something else stops the show. hobot also suggests if following my advise you fib and say just needed nip up a bit more. I don't think ya'd want to dump black pepper in oil to seal it that way. Don't think JBW thin smear would work. If anything of the prior advise applied then it would of puked oil from the get go.

https://www.google.com/?gws_rd=ssl#q=spray+on+sealer

https://www.google.com/?gws_rd=ssl#q=hy ... racer+blue

"Blacksmith hammered"? Jeeeeez

I'm somewhat confused about what you did with the oil piping. The metal tube that protrudes from the top of the oil tank, (it can be either on the top of the oil tank directly or in the 'top hat' thingie, there are 2 versions of the central oil tank) is actually the input to the oil tank from the timed breather port. It just dumps oil pumped out of the timed breather back into the oil tank. The real oil tank breather is internal to the oil tank. Looking at the front of the oil tank, there is a hole that's actually in the air filter area. There's an internal tube that goes from that hole curves up and into that 'top hat' thingie, I look at it as a sort of separator, but it doesn't keep oil vapor out. The only way to keep oil from getting into the air filter area is either plug that hole which will end up closing off your oil tank breather or add a hose to that hole and dump it into a catch bottle. Some people insist that they never have oil coming out of that hole, but I was not that lucky. I drilled a hole through a 5/16 stud, tapped it into that hole in the front of the oil tank and ran a hose out of the air filter into a catch bottle between the trans and engine. It's just a large pill bottle with a plastic T fitting on the end of the tube into the lid of the pill bottle and another hole in the top so it can breathe to the atmosphere. That helped my oil issues a whole lot. You could also add another hole in the top of the oil tank for another breather tube and plug that hole in the air filter area. But I also have oil coming out from the crankcase flange areas due to my lack of experience putting crank cases together. I've pretty much mitigated that leak by adding a cut off valve in the oil feed line (now don't everyone get excited here) and an ignition cut off so the valve has to be open to run the ignition. That helped a whole bunch too, I'm convinced because it limits the wet sumping while standing around for weeks at a time. but I still have small amounts of oil coming out of the crankcase flanges. There's no gasket in there, it's just sealed with your favorite brand of sealer.

I'm not sure I'm helping you much here, but I'm of the opinion that the crankcase flanges need to be sealed very good in order not to have leaks and that most likely can only be done by breaking the crankcases apart. There was a thread a year or so ago about producing a vacuum in the engine by some method and trying to suck some sort of sealing compound into the areas that leak around the flange. That sounds too good to work to me, but it may be worth a try if you could ever get the residual oil off things. I'm sure a good breather would also help a lot, but that again involves taking the engine apart, drilling new holes ala Comstock and adding a breather off the timing cover. At least you have a blanking plate, my bike is a solid casting there.

I toy with the idea of breaking the engine down and re-sealing the flange. It probably really wouldn't take more than a couple days if I had everything ready but it doesn't sound like you want to do that yourself and that puts you at the whim of someone that may or may not do it right, unfortunately.

Good luck and let us know how you proceed.

Dave
69S

Duh yep blacksmith hammering is a common past era mean skill to get weld distorted cases undistorted enough seam closes back up for normal sealing. Its usually done with a flux chipping hammer's sharp end which peckers up the surface like tooth pick into wax. Peel seams had 1/16"+ gaps in waves around the case with like 1/10" up top behind the barrels. Sealed oil tight even after insane over rev event. The mostly now late bunch on UK NOC and Brit Iron told me what I had to do and it about did me in doing the deed over a week of hours at a time. Btw the only reason I got to be intiated Commando mechanic was d/t the 13 leak sites pre-peel had. The couple feet of welding pre-peel needed was cases had cracks DynoDave found at microscopic beginings and then welder uncovered some more melting down into stress riser areas so did the basic old school case reenforcement that saved Peel cases when nothing on DS or TS survived crankwhiplasting rpms.

Could still just be front rocker covers drooling down to the bottom. Best thing going for the rockers is the breast implant soft thick sillycon gaskets.

Thats the problem with getting someone else to rebuild your motor, you don't know what repairs they do, what sealant they used to join the crank cases together or if they used any at all, the mount of oil that is coming out of your motor is way to much and if its spraying all over your rear tyre is so dangours, do what Steve ( Hobot) said give your motor and bike a good clean, if its leaking as much as you say it is it won't take long to trace the leak, if its coming from your crank cases then the only best way to fix it is to pull the motor down, find out what the damage is that has caused the oil leak, maybe all it needs is resealing with non hardening sealer, you might be lucky, but fix it properly if you want trouble free ridding.
If you intend to keep your Norton, them pulling it down yourself will be the best way to learn about your own bike, its not hard to do, have a good workshop manual, take your time and if you have any problems then there are a lot of member here that will help, I had to pull my rebuilt motor down after the rebuild because of crackes around the crank seal that was rewelded but didn't work so had to replace the crank cases, I replaced the cases without to much troubles by leaving the pistons, rings and rods on the crank, I was lucky that I found a good set of crank cases with little milage on them and after 6 years now they have never leaked.
When I first rebuilt my motor in 1980 I had no experance with motor rebuilds, I did a few high performance inprovements to the motor and when reassembled it fired up first kick, so don't be put off doing it yourself, its the best way to learn about your motor, but fix it properly and you will never look back, doing quick fixes will just prolong the orginal problem, but find where the oil is coming from first, it could just be a simple fix if your lucky.

Ashley

Does the bike wet sump? How is the oil return? Is the leak worse at start up or stay the same. If you are starting out with a crankcase full of oil it will try to find creative ways to escape. A leaking base gasket between the barrels and cases can piss a pretty good stream. You can pull the top end off on the bike without removing the gearbox or primary. Worth a close inspection.
If you run ATF in primary you should be able to identify it by color.
Gear lube in gearbox should have a distict odor.

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.

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If the oil is coming from there and you say the motor was professionally rebuilt years ago, then you got to ask yourself why did they put it together with that damage in the first place, maybe they did but looking at that pic maybe they didn't and bodged it up to last awhile after getting your hard urned money, maybe you should ask them, you got grounds to ask even after a few years.

Ashley

The horizontal join you are refering to is the joint between the cylinder block, not the head and the crankcase. This is sealed by the base gasket I was refering to. It can be a real leaker if it goes bad. I had one let go on a Triumph and I went through 2 quarts of oil to go about 20 miles. Time to do some careful diagnosis. Fixing a leaking base gasket is going to be a heck of a lot easier than fixing a leak between the cases. Most amatuer mechanics can do the base gasket with no problem. The fact that it started suddenly sounds to me more like a gasket failing than damage to the surface of the cases. I would have thought damage to the cases would have leaked from the startup.

Base gaskets are taboo to me d/t fairly rapid failure so learned ya can undo the barrel fasteners and head steady and carb boots to lift up enough to get another leak prone gaseket in over the studs or apply a good sealant and crank back down.

Yep that's how I fixed my Triumph. Just took the base nuts off and lifted cylinders and head as one unit. Make sure pistons are at top dead center so rings aren't exposed. Cut the gasket in two, lite coating of Hondabond on both sides, extra smidge at the cuts torqued everything back down. Seven years later and still no leaks. Was wondering if that would work on a Commando. Hobot, how did you deal with the pushrods? On a Triumph they are easy to pop in and out. But they are another leak source

I left the head on especially to avoid the push rod painful puzzling. I used the head oil bolts to zip tie the mass to get goop in but didn't put a gasket in. Unless the rockers very ends ground back its a prisoners puzzle for me, no freedom til solved. With the end ground off almost as close as Dunstall > push rod go either way first time every time. I do hate oil leaks and with all the clutter in life having at least one clean machine is so comforting.

So how is this dangerous leak gonna be tackled first? If surface spray don't do it and its a too wide a gap issue then I'd JBW the seam with good side greased or just razored off while pliable or filed flush once set up. Could be a crack or porous spot finally breaking through. I learned the hard way about stress riser fractures arising deep inside via microscopic grain interface grain by grain till pop goes the weasel.

ChrisT - if you decide to pursue the sealant approach you might want to review the following discussion as there was considerable counsel offered there regarding sealant use for oil leak control.

http://www.accessnorton.com/there-way-t20487.html

As said by others don't be frightened of having a go these motors are not hard to work on and about as simple to understand for a beginner as a four stroke engine gets.

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haha-haha - that's what I was told too last century and stil trying recover. Once ya take engine apart beyond just resealing expect to find about everything needs renewing and a bunch of extra tools or sending off to those that do. Don't sweat slicking a base gasket as there is only low pressure to even vaccum in there, which implies may have oil return passage blocked so wet sumps and dpo stuck in a rough lifter so a cam lobe errorded and was over rev'd in frustration so crank a bit bent and bearing bores loose so a few threaded holes failing on next use. ...