How I finally got my primary chaincase cover leak free !

I have had my 1973 850 over a year now and will not bore you with the many experiments that did not work. I have an Alton inner primary chaincase which is perfectly flat when laid on a piece of glass

There are two factors leading to the leak free solution on my bike.

1) The Norton standard primary chaincase O-Ring seal I was using would quickly deform after one ride, likely assisted by engine and exhaust heat, and go permanently flat where the primary cover presses against it. Therefore I think it is unsatisfactory and I needed an O-Ring that was soft, but would not deform permanently. A softer, non deforming, O-Ring hopefully would spring back and could take up any gap opening up due to chaincase or cover warpage under heat

2) My primary chaincase cover, when laid on a flat piece of glass, has areas that have about 6 thou of clearance gap. The area that leaks is at about 7 o'clock as you look at the primary. Well, it seemed to leak all along the bottom and not just that area! So I needed to find something to fill the 6 thou gap.

The Solution

1) I bought some 60 thou cork gasket material (ie soft) and cut a gasket (actually in three parts) and glued the gasket to the primary cover with Permatex Aviation Form A Gasket (ie not hardening). (I first coated the chaincase cover face with sealant and let it sit three hours. Then a light coat on the cork gasket and pressed them together. I put the cover with gasket side down on a piece of glass for two days to set some more)

2) I wrapped the left side exhaust pipe to stop heat being a factor that either warps the primary chaincase cover or causes the seal to deform.

3) I bought 0.210" silicone O-ring stock from McMaster-Carr as below and put it into the inner primary case groove with a little Permatex Aviation sealant. Went immediately to step 4

4) I put a little sealant on the O-Ring where it will touch the cork gasket when assembled. Went immediately to step 5

5) Put on chaincase cover and torqued to 10 foot lbs and then waited a day for all to set. Went for a ride and it leaked. I then loosened cover bolt, torqued to 15 foot lbs.

No leaks for 4 ride cycles now. I am happy!

Here are some conclusions as I did pull it apart to check if silicone O-Ring deformed

1) It appears that a combination of a soft cork gasket and a soft O-Ring seal are working to stop leaks by compensating for the 6 thou cover gap and any heat caused warpage

2) The silicone O-Ring is not deforming at all like the stock seal does. So it may be that wrapping the exhaust pipe to cut heat is of no benefit. However, it may be that exhaust heat was deforming the primary chaincase outer cover more than it already is and is of benefit.

3) If the above solution eventually fails, there are several things I will try

A) Retorque. If retorque fails, I will inspect how much cork gasket has been compressed. It could be cork gasket degrades and destructs
over time due to vibration or heat or something.

B) Use Permatex The Right Stuff instead of Permatex Aviation to glue the cork gasket to the chaincase cover and lay on flat
glass to set as it would permanently fill the 6 thou gap (ie not deform and ooze out when chaincase cover is tightened)

C) Try a square profile O-Ring. McMaster Carr (see below) has one (I bought some of it too) This would have more surface area pressing
against the cork gasket. However it is not as soft as the silicone O-ring. It's a maybe. If anyone wants to try the
square profile O-Ring, I am happy to mail them enough of it to try !

I hope this might be useful to you and thank you all for the help you have given me since I joined the Forum!

And I will report if it fails.....

Dennis
Vancouver

McMaster-Carr part 5229T53 high temp soft silcone o-ring stock 3/16" actual 0.210" 20 foor length $42.80 Cdn

McMaster-Car part 9700K13 square profile (o-ring) is also 0.210" (but it is harder)

9700K13

High-Temperature Soft Silicone O-Ring Cord Stock 3/16 Fractional Width, 0.21" Actual Width, 20 ft. Length

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The O ring sealing gasket in a kick start primary will go flat when the outer case it put on. that is normal but the biggest problem people just over tightens the middle primary case nut, they think the tighter the better it will seal, but as you found over tightening the outer primary case will pull the centre of the case in and cause the front and rear of the case to warp and that leads to oil leaking, from that bolt being over tightened, all new owners make this mistake and I have also done so in my early days of own my Norton from new.
I had to replace my inner primary case got damaged when I threw a chain while doing a burn out in my youth but before I replaced the inner case I cut it open at the rear and cut vents in the front of the inner case to run a belt drive to let cool air flow through it, worked great but after a few good years running the belt drive and the last 12 months having running issues with the belt I decided to go back to the primary chain so I got a good second hand inner primary case to replaced the damaged/cut up inner case.
Going back to what I was saying about over tightening the centre mounting nut for the outer primary case, a new O ring seal and I just nip up the centre nut tight enough to not to be too tight that it will warp the outer case, well that was over 20+ years now and I use no sealant at all on the O ring, yes the outer case side of the O ring does go flat as it should and still has enough rubber to seal the primary and I say the mounting nut would have less than 10ftlb on that nut when installed, my primary has never leaked since doing it this way and I do run transmission oil in the primary so no drops of red oil under my Norton, I am still using my original outer primary case.
So conclusion, never over tighten the centre mounting nut as all that does is warp the outer case and cause the primary to leak oil, I can remover the primary outer case many times using the old rubber O ring seal, I always leave it in the groove of the inner case when I go inside my primary and only replace it when it been reused too many times, I buy a big roll of O ring rubber and cut to size, heat does not cause the rubber to leak only over tightening the primary outer case that does that, even with so little pressure on the mounting nut, it has never come loose.

Ashley

When I got my bike and then installed the Alton, I had massive primary oil leaks as I didn't use a torque wrench and tightened lightly. Then I used a torque wrench and at 10 foot lbs it started to leak less and the same at 15 foot pounds.
It may be that my cover is the problem but the solution I found seems to have finally solved the problem.
Dennis

Yes but should never have a problem in the first place if done right, next time your cover is off put it on a sheet of glass to see if it's warped, usually they come good after being undone.

I did lay it on glass and it is warped!
Dennis

I Have a Mklll so a bit different, but I do remember a thread a while back about the importance of shimming the backside of the primary when mounting (it appeared to be a sort of common problem for a washer to have been left of when reassembling - usually from a previous owner, "back in the day"). You may have already address this when adding the Alton, but thought I'd mention. Cj

DennisMo said:

I did lay it on glass and it is warped!
Dennis

Click to expand...

When not warped, no junk added, not over tightened, and the seal comes from AN, they do not leak. No torque wrench. Tighten until the gap is even and about 1/16". If you put a washer on the stud before putting the outer cover on, remove it - the parts drawing is confusing - no washer there.

.006" is a lot of gap. If you have a surface plate, fix that.

BTW, everyone I've ever touched that had sealant leaked. When I was able to get rid of the sealant and install a new O-ring, the leak was gone except when the cover was warped beyond repair.

I did shim the inner primary properly so there would be no warping of inner primary when tightening the outer cover on

Dennis