I’ve finally managed to track down a new pair of Lafranconi Competition pipes for my LM1 which arrived yesterday. Looking in the box, the balance pipe comes with some fairly ineffective looking ‘O’ rings which I assume fit inside the female recess in each silencer? - it seems they disintegrate with temperature, wondering if there’s an alternative or should I use some high temp sealant that doesn’t go hard like other exhaust paste does…any suggestions most welcome…thanks
I resorted to car exhaust repair bandage and Gun-Gum. I’ts not permanent fix so you have to redo periodically. Especially just prior to an MOT test!
Sounds unlikely, but I’ve found that bathroom sealant/shower sealant works as good as exhaust sealant and lasts as least as long.
permatex ultra copper high temp gasket maker might be worth a look.
It is supposed to withstand temperatures up to 700 degrees F (371c)
Malc
I understand Gun Gum in the joints before clamping them up but where would you wrap exhaust repair bandage on a Mk1 Le Mans without it looking like a bobber?
Wrap a short bit around each end of the balance pipe, before inserting into the silencer holes. Because there are supposed to be O-rings, the “fit” is quite loose without them so need something to fill the gap. At least I think that’s how it went, was a long time ago. 
There are no clamps, only O-rings. So when the O-rings have burnt away, the tube is looser than a rattly leaky loose thing. 
And therin lies the problem, buy clamps.
mine has rattled happily for years
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The bike I’m working on has the balance pipe well and truly stuck in the r/h silencer. I was wondering how to get it apart! Don’t think I’ll bother. The l/h one didn’t exactly fall off either. No sign of o-ring in that side. Once I’ve fixed a loose baffle in the left silencer I might braze it all together!
You need to actually see a set of these silencers, to see how daft it is. The tube stubs on the silencers are larger than the crosspipe, to the tune of the thickness of the O-ring (albeit it’s recessed in a groove). You would need to cut slots, so the the stubs would compress with a clamp over the top, but I’m not sure they will compress enough.
Today I remembered wrapping exhaust bandage around the outside, at each side of the crosspipe, using the Gun-Gum or whatever similar is in the kit, then jubilee clips on top to keep it all together. That way the gaps, vacated by the missing O-rings, could be filled.
I ought to add, the reason for that palaver is because the Gun-Gum filling method I’d used previously kept being blown out with subsequent use.
I used these. Seem to work for me Viton O Rings: High Quality Viton Rubber Seals & O Rings
Some info here.
https://www.barnwell.co.uk/temperature-range-of-viton/
I’d have to go searching for confirmation, but I recall some years back a bit of a flap in the automotive industry re Viton o rings that got overheated and somehow exuded hydrofluoric acid, which you don’t want on your skin. It wasn’t my area so I didn’t take a lot of notice at the time.
And, Lo, it was a bit of an unnecessary flap… (though still doing the rounds, I guess we can believe the HSE)
https://www.hse.gov.uk/mvr/topics/fluoroelastomers.htm
Atb
Simon
Very interesting thanks.
What size did you get?