Persistent Primary oil leak (2016)

I've run up against a problem on my '75 850 that has me stumped and I could use some advice from the collective mind.

A while back it developed an oil leak on the primary side. After taking it out for a ride I'd get a few drips of oil right below the left foot peg. Not a lot, maybe a teaspoon or two. I would find oil dripping from the bottom of the primary case. It would be all over the frame, the left half of the center stand, and the kickstand. There was no oil forward of the foot peg.The oil filter was dry, no leaks there. There would also be a light film of oil on the inboard face of the inner primary case but nothing that pointed to a definitive source of the leak. As far as I could tell it was probably the seal behind the clutch in the inner primary case so I went ahead and tore it down. When I put the inner case back on the bike I made darn sure to not damage the seal and that it was installed facing in the right direction. I also checked to make sure that the seal was concentric with the drive shaft from the gearbox. It looked just fine. Took it out for a test ride and the leak was still there. I know it's not coming from the primary inner case mounting stud forward of the gearbox seal or the seal between the primary and the crankcase. At the end of a ride I immediately check it out, but so far I can't be certain where the oil's coming from because it's been blown all over the areas I've described. I'm just going through a process of elimination and assuming it's the seal.

So here's the problem. It only leaks when I'm riding it. I have cleaned off all the oil and then run the bike on the center stand revving it up like on a ride. I've even leaned it from side to side and it stays dry as a bone.

I'm thinking that it may be that I'm getting some relative movement between the gearbox and the primary case, causing the seal to open under load. All the engine and gearbox frame bolts are torqued correctly and I can't see any signs of movement.

Could bad isolastic mounts cause these symptoms?

Hope somebody's got some experience with this. Any advice will be most welcome and please forgive if this has been discussed on a previous thread. I couldn't find any when I searched. Thanks.

rdleeart said:

I know it's not coming from the primary inner case mounting stud forward of the gearbox seal or the seal between the primary and the crankcase. At the end of a ride I immediately check it out, but so far I can't be certain where the oil's coming from because it's been blown all over the areas I've described. I'm just going through a process of elimination and assuming it's the seal.

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Assuming your "1975 850" is a Mk.3, then there are other areas at the rear of the primary case where oil could potentially be leaking from, such as the gearchange cross-shaft seal, alternator grommet, or, perhaps less likely, the starter motor O-ring.

L.A.b. is correct. However how about something so basic people tend not to think of it......how much oil are you putting into the chain case?? It should be 200cc or 7 fl oz. Filled to the level plug on a friends pre Mk3 and it contained 290cc. Quote Mk3 Workshop Manual section K8.' Note: under no circumstances allow more than 7 fl.oz. (200 cc) of oil in primary case'.
Whilst this instruction was given AFTER the then Service Manager John Nelson had investigated the serious clutch slip problem they had from day one of Commando production so that the chain just touched the chain and created an oil mist for chain lubrication any extra would result in oil being sprayed around in greater amounts which could possibly be the cause of your problem..... Just for a laught go stick your pinky on your primary chain and get a friend to put a boot on the rear chain and note the effect on primary chain tension. It is a pretty good indication of the wear and movement within the gearbox / sleeve gear bushes. On BSA unit singles the oil seal never actually seals all the way round the shaft and can be anything up to 0.010 inch off centre..a problem well known about in the factory and explains why the oil seals are often untouched on one side!! Wonder if the Norton seal is correctly positioned??
DO NOT MAKE THE MISTAKE, AS MANY DO, OF ASSUMING THAT BECAUSE THE CLUTCH IS WITHIN THE OIL BATH CHAIMN CASE THAT IT WAS DESIGNED TO BE RUN WITH OIL ON THE FRICTION INTERFACES. Had you been around, as i was, to talk to people such as Phil Heath who was part of the Norton 1930s oil bath chain case development team you would of learnt that they shoved a designed to be run dry clutch within the oil bath chain case....that the correct oil to employ was a straight SAE 10 or 20 oil and that the CORRECT level was till it was touching the bottom of the chain...just like the BSA Gold Star filling instructions......which also employed a designed to be run DRY clutch within the oil bath chain case.

J. M. Leadbeater said:

DO NOT MAKE THE MISTAKE, AS MANY DO, OF ASSUMING THAT BECAUSE THE CLUTCH IS WITHIN THE OIL BATH CHAIMN CASE THAT IT WAS DESIGNED TO BE RUN WITH OIL ON THE FRICTION INTERFACES. Had you been around, as i was, to talk to people such as Phil Heath who was part of the Norton 1930s oil bath chain case development team you would of learnt that they shoved a designed to be run dry clutch within the oil bath chain case....that the correct oil to employ was a straight SAE 10 or 20 oil and that the CORRECT level was till it was touching the bottom of the chain...just like the BSA Gold Star filling instructions......which also employed a designed to be run DRY clutch within the oil bath chain case.

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Please could you TRY to STAY ON TOPIC, and not use every available opportunity to turn things into a CLUTCH discussion.

A Mk.3 (as this model appears to be) needs more than the minimum amount of oil in the primary, otherwise the hydraulic tensioner will not work correctly, so while filling the primary until the oil "touches the bottom of the chain" may be perfectly acceptable for pre-Mk.3 Commandos I wouldn't recommend it for a Mk.3. Even with what could be considered an additional amount of oil in my Mk3's primary case the standard bronze plate clutch doesn't slip-so could we now perhaps get back to the original subject.

Guys,thanks so much for your comments. My apologies for not mentioning that it's a Mk3 Commando.

Many times have I checked the alternator grommet, crossover shaft, and starter. Dry.

As far as fill level goes, I have always filled it by allowing the excess oil to drain out of the drain plug while the bike is on the center stand. Always seemed to be ok til now. Maybe I need to reevaluate that.

rdleeart said:

As far as fill level goes, I have always filled it by allowing the excess oil to drain out of the drain plug while the bike is on the center stand. Always seemed to be ok til now.

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Reducing the amount may slow the rate of leakage, but I doubt it's actual cause of what would seem to be a relatively recent problem.

I agree but will give it a try just to cover my bases. Ain't holding my breath though.

A point to consider is the rear main seal. Can you drain excess oil from the primary after riding the bike. If the oil level in the primary appears to be the same, then your main seal may be ok. If the oil level increases, then suspect the main seal is leaking, and that will cause oil to come out the main shaft seal area on the clutch when the primary become overfull. Sorry, I don't have a mkIII so I my be barking up the wrong tree here. Happens with the earlier commandos.
Dereck

kerinorton said:

Sorry, I don't have a mkIII so I may be barking up the wrong tree here. Happens with the earlier commandos.

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Yes, you could be right, as the Mk.3 has a 'fixed' oil seal instead of the sliding felt seal on a pre-Mk.3 Commando. If the sleeve gear bushes are worn then perhaps the sleeve gear is getting pulled out of alignment far enough for oil to get past the seal?

Here is my two-cents worth on leaking primary chain cases.
I've owned 'Pa' my MKIII since new and have chased many oil leaks on the primary side;
. the grommet for the alternator wires
. the seal for the shift rod (both inner and outer case)
. the seal for the transmission shafts
. the welch plug on the inner cover fell out leaving a 1/4 inch hole that oil virtually poured out of
. the support stud had oil leak past the washers

A lot of these leaks were caused by the engine main seal that had been blown out from starting a wetted sump and causing the primary chain case to fill with engine blow- by pressure and pushing oil out any place it could.

I also added a vent to relieve the pressure build up inside the cover, the vent is similar to the vent used on the transmission case.

Another problem is that the inner case with the seal for the transmission is NOT self locating! If the case is simply installed and tightened down the shaft and seal will not be properly aligned and oil will pour out at the transmission shaft.
Another Norton friend and I have developed a two part spacer, the first part saves the seal as the case in installed over the shaft, the second part fits over the first to locate the case to the shaft.
I'd show you a picture but I'm not computer savvy enough to do that.
Ride On
Dave

The Buckeye Rider said:

Here is my two-cents worth on leaking primary chain cases.
I've owned 'Pa' my MKIII since new and have chased many oil leaks on the primary side;
. the grommet for the alternator wires
. the seal for the shift rod (both inner and outer case)
. the seal for the transmission shafts
. the welch plug on the inner cover fell out leaving a 1/4 inch hole that oil virtually poured out of
. the support stud had oil leak past the washers

A lot of these leaks were caused by the engine main seal that had been blown out from starting a wetted sump and causing the primary chain case to fill with engine blow- by pressure and pushing oil out any place it could.

I also added a vent to relieve the pressure build up inside the cover, the vent is similar to the vent used on the transmission case.

Another problem is that the inner case with the seal for the transmission is NOT self locating! If the case is simply installed and tightened down the shaft and seal will not be properly aligned and oil will pour out at the transmission shaft.
Another Norton friend and I have developed a two part spacer, the first part saves the seal as the case in installed over the shaft, the second part fits over the first to locate the case to the shaft.
I'd show you a picture but I'm not computer savvy enough to do that.
Ride On
Dave

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Ok here is the link to the pictures of the seal protector/locator developed by Milfodite and I.

Ride On
Dave

The Buckeye Rider said:

Ok here is the link to the pictures of the seal protector/locator developed by Milfodite and I.

MKIII primary alignment tool

My pal Dave Mathers and I were trying to come up with a way to keep the primary case from leaking at the mainshaft seal. When Dave was putting his bike back together after a rebuild due to a malfunction of the check valve in the oil line, it became apparent that the inner case was not lining up...

www.accessnorton.com

Ride On
Dave

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Hi Lads,

I know this discussion is from 2016!

does anybody know of a commercially available seal locator/protector for the transmission shaft seal?

I think I’ve seen one for up to 1974 which I presume will not work on a MK3 as it uses a different seal.

Trying to trace a primary leak myself, my mates just say at least I know there’s oil in it!!! But I’d like to keep most of it inside the bike!

Additional question: how important is it as to which type of oil you are using? How different is the Mk III
situation from the early models?

click said:

does anybody know of a commercially available seal locator/protector for the transmission shaft seal?

I think I’ve seen one for up to 1974 which I presume will not work on a MK3 as it uses a different seal.

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I see no reason why one would be necessary. The Mk3 seal is fitted to the outside of the inner primary case and locates against a shoulder in the case but with the seal lip to the 'oil' (primary) side.
As long as there are no sharp edges on the sleeve gear then (with a little oil or grease applied to the seal lip) the seal should slide over the sleeve gear without damage.

L.A.B. said:

I see no reason why one would be necessary. The Mk3 seal is fitted to the outside of the inner primary case and locates against a shoulder in the case but with the seal lip to the 'oil' (primary) side.
As long as there are no sharp edges on the sleeve gear then (with a little oil or grease applied to the seal lip) the seal should slide over the sleeve gear without damage.

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True, assuming that the seal is perfectly centered on the shaft. Using the tool that Buckeye Rider and I built, I had to loosen all mounting points, and use ratcheting straps to pull the engine and gearbox into place to get it centered perfectly. Then try to get everything tight without it moving around! No easy task. I suspect that all other seals and gaskets are in good shape, this seal causes most of the MKIII primary leaks.

milfordite said:

True, assuming that the seal is perfectly centered on the shaft. Using the tool that Buckeye Rider and I built, I had to loosen all mounting points, and use ratcheting straps to pull the engine and gearbox into place to get it centered perfectly. Then try to get everything tight without it moving around! No easy task. I suspect that all other seals and gaskets are in good shape, this seal causes most of the MKIII primary leaks.

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I did have the entire primary, stripped about two years ago chasing the same leak, put in new seals on the gearbox drive shaft & gear change crossover rod + a new grommet for the alternator cable but the leak was still there, possibly worse!!!

I can't remember for sure but I don't think I used any sealant on the crankcase to inner chain case gasket which I think is the cause of my leak (just used some grease). I can't see any oil further down near the gearbox drive shaft seal area. It looks to me that it's coming more from the front. I'm pretty sure the outer case is sealed well. I have chased other leaks before & it's amazing how oil can move around the outside of an engine in a totally counterintuitive way!!

Thanks L.A.B. for your reassurance about the gearbox drive shaft seal, I know when I did the original strip & re-assembly this part of the job seemed simple.

I also note what Milfordite has said & when I get around to stripping the primary again over the winter I'll pay particular attention to how centered the seal is!