Hylomar sealant

They also offer a Mk3 850 primary, cylinder base and timing cover gaskets, all in the Nitrile and aluminium, however I don't have part numbers for those. Cometic Sales should be able to look it up.

Glen
 
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https://www.cometic.com/ It might involve a phone call in regards to Norton as nothing is posted on their site, and worntorn only posted part #'s for a couple of specific parts. In the Harley world, I have used them for 25+ years. Nitrile coated aluminum. I had a failure on the 3 piece EVO rocker boxes/ valve covers once. But that was unusual as I never had a problem before. I always used them for parts that would come off more frequently, like the primary or primary inspection gaskets. I think someone posted on here before that there were quite a few options for the vintage Commando from Cometic. For the 74 Norton's I use the JSM reinforced rubber gaskets.
 
We have been using Permatex Aviation Form-A-Gasket with very happy results on lots of British bikes. Replaces Wellseal which was the AJS recommended sealant. like a much tackier hylomar and more heavy duty but cleans very easy with alcohol/methanol.
 
Permatex Moto-Seal. Used it on everything from two cylinder Nortons to 12 cylinder Detroit Diesels! Moto-Seal is NOT a silicone (tool of the Devil)!!
 
MexicoMike said:
Permatex Moto-Seal. Used it on everything from two cylinder Nortons to 12 cylinder Detroit Diesels! Moto-Seal is NOT a silicone (tool of the Devil)!!
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Pretty sure that is a suitable substitute for Yamabond 4, Suzi, Kawi, Honda, all Threebond 1184 from Japan.

All great stuff.
 
One more thought on the MK3 oil tight situation. The cases are rarely straight, most of the british makes of this era are off. Unit BSA and Triumph are wildly off, I took 0.013" off the primary side on a BSA A65 case yesterday and as I recall I took nearly as much off of my mk3 inner case and spent a ton of time lapping my outter case to get a flat surface. The silicone gasket JS sells is a great gasket, but no matter what you need relatively flat cases.
 
Mart UK said:
I don't know the earlier Commandos, as mine is a mk3. For the mk3 there is a silicon gasket available: https://jsmotorsport.com/product-category/norton-gaskets/. This was to be my next attempt, if the grease didn't work.
Might be worth making contact to see if something similar might be made for the earlier primary covers?
Edit: they are reusable, I have them on my tappet covers.
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Have you used them on the MK111 primary? If so for how long? I would like to know the long term effectiveness, ie leakes.
 
worntorn said:
I can't imagine going back to sticky Silicone type sealants anywhere there is a gasket. I went a little crazy and had Cometic make a complete set for the BSA A10, three sets for the Vincent twins (2 now in place) and a set for the Norton Commando MK3. I ordered a dozen of the intake stub type gaskets as they work so well to seal that up without having any sticky stuff that requires removal for reassembly.

The Vincent people tend to be really old and set in their ways, but they have almost all gone over to these Cometic Nitrile/ Aluminium gaskets. A member of the Chicago club made us aware of these gaskets about 15 years ago. At first they just had one or two Cometic gaskets available foe the Vincent but now complete engine sets are available.

I posted info about the Cometic gaskets on the A10 site and the response was " My bike doesn't leak a drop with paper gaskets. And I can reuse them easily"
Yeah, right.
View attachment 113310View attachment 113311
I'm holding up a very skinny A10 gasket by one point and it keeps its shape. It will also do this after many reuses. Try that with other gasket types.
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Well, $37.00 delivered for one MK111 gasket is kind of steep
 
uneasy rider said:
Well, $37.00 delivered for one MK111 gasket is kind of steep
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I would order some additional items to go with it. You can fit a lot of gaskets into one $20 flat rate box, or just one primary gasket.
The intake stub gaskets are sure nice to have as are the rocker cover gaskets. I was told that Cometic has gaskets for the entire engine /trans.

If one wanted to order a paper MK3 primary gasket from Andover the shipping cost to me is about $35 for the cheapest option or $130 cdn for speedy service. Same thing though, they could fill the box with gaskets for the same shipping cost.

Glen
 
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concours said:
Pretty sure that is a suitable substitute for Yamabond 4, Suzi, Kawi, Honda, all Threebond 1184 from Japan.

All great stuff.
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At Pokes Cycle we used Yamabond/Hondabond/Threebond on many joints and it did stop leaks. We used RTV silicone on the rubber band on pre-MKIII primaries, letting it set up before adding oil. Since removing the primary cover was/is a regular service procedure when cleaning clutches, anything more permanent seems ill advised.

The Boss, Ross, added up all the places an AMC gearbox could leak and came up with something like 68. Threebond didn't stop them all, just most of them. But then there is the issue of getting things apart later. It ain't fun. And given the number of MKIII primary cases with ugly chisel marks from trying to break the factory-gasket seal I would never use Threebond or anything even slightly sticky. Silicone gaskets seem like the best solution, though they weren't available back in my for-hire wrenching days so I have no personal experience. I have used similar gaskets on truck engines and they seem to work well.
 
worntorn said:
I would order some additional items to go with it. You can fit a lot of gaskets into one $20 flat rate box, or just one primary gasket.
The intake stub gaskets are sure nice to have as are the rocker cover gaskets. I was told that Cometic has gaskets for the entire engine /trans.

If one wanted to order a paper MK3 primary gasket from Andover the shipping cost to me is about $35 for the cheapest option or $130 cdn for speedy service. Same thing though, they could fill the box with gaskets for the same shipping cost.

Glen
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I get my supplies and parts from Fair Spares New England, fair price and no shipping.
 
DennisMo said:
I have a leaking primary case problem (1973) that I have battled for while.
It does not leak when I put the seal in, with sealant, let set and then fill with oil.
I use sealant along the bottom face. (I have tried blue silicone, Permatex The Right Stuff and Permatex Optimium Black)
I can leave it for weeks and it will not leak.
But when I take it for the first ride, it leaks from the bottom and every ride thereafter.
I have properly shimmed behind the case where the bolt tightens the
cover to the inner primary.
When I lay the cover on the inner primary case without a seal, it is flush everywhere
Would really appreciate your thoughts
Thanks
Dennis
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Have you ever drained and measured the amount of oil in the primary. If the crankcase is wet sumpted and the inner primary screws allow that to leak into the primary, you may have way too much in the primary.

With a good big o-Ring and good inner and outer covers, there is no need for, and you should not use sealer on the o-Ring.
 
My 74 850 has never has silicone sealant or anything on the large O ring seal in coming up to 48 years of ownership, I use ATF at 7floz in the primary, my 3 inner screws are all sealed to stop motor oil and I don't have a clutch seal on my clutch rod, the only way GB oil get down the clutch rod is if the GB is over filled, but I do put grease on the clutch rod.
My primary outer case has never leaked as I never over tighten the outer case centre nut, I have never had to top up the primary oil between servicing.
I learned a long time ago the level tube in the GB puts more GB oil in, I measure my GB oil in a measuring cup to the recommended level in my manual, so no GB oil down the clutch rod problem.
I buy a big roll of O ring rubber for my primary case and cut to size and replace the O ring seal when it gets too flat or when the outer case has been removed a few times, since using ATF in my primary my clutch plates have never stuck or has the clutch slipped, I am still running the original clutch plates, but have replaced the clutch centre once as well the outer pressure plate about 15 years ago, my Norton was a every day rider most of it 48 years of life with me.
I have replaced the slide seal on the inner primary case behind the clutch housing once about 15 years ago as I had to replace the inner case from a mishap.
When I brought my Norton new at 17, my mate Don who got me into Norton's told me to never over tighten the outer primary cover and you won't have any problems with oil leak, very sound advice, but took me a few years to find the right oil to prevent clutch slip and stuck clutch plates lol, ATF-F is the best.

Ashley
 
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