Hylomar sealant

uneasy rider

uneasy rider

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Oct 29, 2023
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So, I have read that you can use Hylomar on a MK111 primary case with no gasket. I see there are different ones, wondering if this will work and witch one will work?

Pls
 
On my mk3, I have an inch of primary case that's a bit dodgy. Doesn't provide a good seal against the cover. I use a light coat of grease on both sides of the gasket and to my surprise, this has provided a long term fix. It also makes it easier to remove the gasket. Last time, I reused it.
 
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
 
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.
 
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
Click to expand...
Are you certain it's from the chaincase seal?
It sounds very much like it's from the sealing plates behind the clutch
 
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.
Click to expand...
Those Real Gaskets work ok as reusable for something like the rocker covers but are a nightmare to reuse on the primary. First installation works fine but after one use they are difficult to get to stay in position and must be installed dry. I found out when I didn't have a paper gasket on hand as the Real Gasket is touted as reusable. I didn't have any leakage but will never try to reuse again. The minor leakage that a paper gasket may exhibit just doesn't matter to me. In fact, I didn't have any leakage with one I just liked the reusable feature which isn't worth it.

My airplane engine had one on one of the rocker covers. It's so soft that whoever put it on, probably to stop a leak, bent the casting. I lapped it on a sheet of glass and installed it with a paper gasket and it doesn't leak.
 
I'm sold on Cometic gaskets for this purpose.
The Cometic Nitrile/Aluminium gaskets are available for the MK3 primary. I installed one some time ago and have had the cover off a couple of times since, once to replace clutch plates and once just to have a look around.
The gasket is still like new and will stand up to many reuses. They provide a perfect seal, even if the mating surfaces aren't perfect.
I used the Cometic Nitrile gaskets all over the engine/trans when assembling the 920 engine.
Because of the aluminium centre they hold their shape perfectly and look very neat as well.

Glen
 
A few weeks ago I checked the Amal carbs en reinstalled them. My tube of Hylomar Universal Blue was about empty so I tried to buy a new one. Not so easy. It appeared that it had been replaced by Hylomar M. Universal Blue uses methylene chloride as solvent, M uses acetone. I gave it a go and bought the M.
For the carb, just a very thin smear for the bowl gasket and the manifold joint, just as an assurance.
I found the acetone version is less "tackier" when applying and it dries quicker. Not an improvement in my view. It is not in an oily area and it is only a short time ago so cannot tell yet whether it seals better or not.
 
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.
Hylomar sealant
Hylomar sealant

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.
 
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.
Click to expand...
Link?
 

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