Leaking Primary Cover

Hello. This seems like a simple problem, but I replaced the primary cover o-ring with a new one from Andover Norton on my '71 Commando and it drips abou half a teaspoon of oil after a short ride. I read about shimming the center mount for even gap around the cover without the gearbox, but not sure how to do that. Going to pop it off and check more closely for an obstruction like grit or a burr, or a crack. But figured twenty other people probably had the same problem so checking in with the pack. Any thoughts? Thanks in advance.

Don't over tighten the centre mounting bolt on the cover, over tightening will warp the cover and it will leak, lot of new owners get this wrong, some learn quicker than others, if the shimming is wrong behind the inner primary case you will know about it as not much room between the chain and inner cover.

tried a new o-ring, checked the groove and flat surface, both clean. checked with no o-ring and cover touches primary case all the way around. torqued to 25 ft-lbs per access threads, ((seemed a little much). used a little smear of hylomar on the flat surface of the primary, per internet suggestion, but maybe a mistake, because it still leaks. very frustrating. Will try slathering the o-ring with gasket glue on the next (third) attempt. If that doesnt work perhaps a belt drive.

I think they were vacum cleaner drive belts .

youve checked theyre both FLAT ? the faces / surfaces . Dress with sledge hammer , lightly . On wooden blocks .

A ' tip ' for older tin Norton primarys was to tip boiling tallow in , with the bottom run level , to seal it .

Mine always had a drop or two . stops things rusting . Be a Man and like it ! .

Big Red said:

tried a new o-ring, checked the groove and flat surface, both clean. checked with no o-ring and cover touches primary case all the way around. torqued to 25 ft-lbs per access threads, ((seemed a little much). used a little smear of hylomar on the flat surface of the primary, per internet suggestion, but maybe a mistake, because it still leaks. very frustrating. Will try slathering the o-ring with gasket glue on the next (third) attempt. If that doesnt work perhaps a belt drive.

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Are you sure it's leaking from the O ring and not from the sliding plate behind the clutch?

The big o-ring needs to be fitted with it's casting mark to the top to avid leakage at that seam . Also : smear the whole o-ring heavily in grease . Shimming the support correctly is critical , so that no warpage occurs between inner and outer cases . Flat to flat .

I have never used grease or any sealant on that rubber but I did learn a very long time ago not to over tighten the centre nut for the outer cover, mind don't leak a drop from the primary cover, but its also been a very long time since I been inside my primary.

Thanks for the replies and advice. It looks like the outer cover deflects a bit as the center but is tightened, so I am questioning if it was shimmed right. Does correct shimming mean taking off the entire primary to shin behind the inner cover and bring it out relative to the center post? I was considering trying shims on the center post to prevent the outer primary pulling in so much to avoid pulling the whole primary apart. Is that a bad idea?

ashman said:

I have never used grease or any sealant on that rubber but I did learn a very long time ago not to over tighten the centre nut for the outer cover...

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Exactly!

In fact, I clean both the inner and outer chain cases with denatured alcohol and if reusing the O-ring, it too. If the O-ring is flattened, I replace it. I tighten until there is an even gap between the covers of about a scant 1/16" (about 1.5mm). They don't leak unless something is bent/warped/chipped.

All I've work on that had sealer leaked until I cleaned it up and replaced the seal. I did have to replace one outer cover because it was warped due to over tightening, and I could not convince it back to flat and it was too warped to flatten.

Big Red said:

Thanks for the replies and advice. It looks like the outer cover deflects a bit as the center but is tightened, so I am questioning if it was shimmed right. Does correct shimming mean taking off the entire primary to shin behind the inner cover and bring it out relative to the center post? I was considering trying shims on the center post to prevent the outer primary pulling in so much to avoid pulling the whole primary apart. Is that a bad idea?

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Shimming is done while installing the inner chaincase. Unless under shimmed and the back is resting on the swingarm which can warp it, it has nothing to do with your problem. There are no/must not be any shims between the inner and outer chain cases!

25 ft-lbs seems way high for the center fixing bolt. I recall the Old Brits torque tables showing 15 ft-lbs for it and thinking that seemed more than needed.
I use gasket sealant (automotive black silicone or polyurethane?) between the outer cover flat edge and the siide of o-ring it contacts, none in the groove of inner cover.
I run ATF F in primary so a leak is more easily distinguished from an engine, swing arm or gb leak.

As Greg has said you only tighten the centre nut till there is pressure on the rubber seal then just a light nip, if you keep tightening it, it will slightly warp the outer cover, squash the rubber seal to much and it will leak there has to be the same clearance all around the outer cover without squashing the rubber too much there has to be a slight gap.
I always run ATF F in my primary so any leak is shown if the cover is leaking, if the rubber hasn't been over squashed it can be reuse many times without any sealant used and replace it if the outer side has squashed too much.
I pull my primary cover off yearly for major service (depends on how many miles I have clocked up in the year) as well to make sure primary chain is good as well service the clutch plates and make sure everything inside is good, it's all part of general maintenance.

Ashley