Which exhaust sealant?

[Ranburetta]

Had a slight exhaust leak between barrel and u-bend - ally barrel, copper gasket, clubman mild steel u-bend.

Don't really want to use Firegum or similar and would prefer a silicone type product but I am not sure what would be up to the job given the high temperature involved.

Loctite 5990 Copper Silicone Sealant has been suggested - what do you think/do you use?

[ULC Soulagent]

Yip that sealant is fine

[rossclark]

I've also used that for exhaust, base and head.

[Warkton Tornado No.1]

As it happens, I've just checked over my engine & previously I used Loctite 5990 Copper Silicone Sealant on the head & exhaust. The exhaust sealant had let go a little @ the top (solid copper gasket) but I shall give it another go.

This time, I've annealed the gasket (heat up & quench) & although I lockwire the nuts together, I might use higher tensile cap head (M7) screws lockwired in place as the barrel has cast iron holes (Rapido)

Loctite 5990 Copper Silicone Sealant is petrol proof so should be better than the bathroom silicone that I've used previously with no issue, but I'll have to keep an eye on it.

[nsaints]

Off the op's topic. Regarding exhaust manifold nuts

I've used these nuts on the exhaust manifold with a lot of success
They're not cheap but they work were other methods I've tried have failed

https://www.merlinmotorsport.co.uk/s/bo ... ngs/k-nuts

Back on topic I use loctite copper sealant. Been reliable so far

[Warkton Tornado No.1]

Off the op's topic. Regarding exhaust manifold nuts

I've used these nuts on the exhaust manifold with a lot of success
They're not cheap but they work were other methods I've tried have failed

https://www.merlinmotorsport.co.uk/s/bo ... ngs/k-nuts

Back on topic I use loctite copper sealant. Been reliable so far

I've been using k-nuts for racing since the 90's & swear by them, but even though I have M7 I've never gone away from having a mechanical fixing on the exhaust. That said, my lockwired fixings have never given trouble.

Perhaps I have a mental block because you are right to use them, if they work for you, though I must admit my M7's don't have the captive 'loose' washer nor are they the type for elevated temperature.

[Ranburetta]

Thanks to all for your advice.

I'm no expert but reasoned that the different rates of expansion of the ally barrel, gasket and steel manifold might have accounted for the slight leak and was looking for a sealant with some flexibility and it seems as though Loctite 5990 might fit the bill.

I have always used the 'standard' brass crush nuts fitted the 'right' way round but I might give the high temp flanged K-nuts a try.

[Warkton Tornado No.1]

Thanks to all for your advice.

I'm no expert but reasoned that the different rates of expansion of the ally barrel, gasket and steel manifold might have accounted for the slight leak and was looking for a sealant with some flexibility and it seems as though Loctite 5990 might fit the bill.

I have always used the 'standard' brass crush nuts fitted the 'right' way round but I might give the high temp flanged K-nuts a try.

The K nuts are a safer bet than the standard fittings IMHO, but as I have lock-wiring kit to hand & either M7 cap head socket screws (or long M6 hexagonal nuts with an M7 tap run through) & a pillar drill to allow them to be wired, that's what I've done tonight....along with some more Loctite 5990

Good Luck with yours!

[nsaints]

For what it's worth here's my tips for a successful exhaust manifold seal
I'm no expert, however this method works for me

1 - good condition, high tensile exhaust studs
2 - studs loctite'd into the barrel
3 - solid copper annealed gasket - make sure all burrs are cleaned off the gasket before annealing and the gasket fits onto the studs without forcing it on. I've opened up the holes 0.5mm so the gasket slides into position without forcing it on.
4 - ensure the manifold on the exhaust is flat, and not bowed/distorted
5 - when ready to assemble, clean all faces with a degreaser to ensure good sealant bond
6 - use loctite copper sealant, allow to cure slightly for a short time (20 mins)
7 - assemble using new k-nuts (I have read k-nuts can be used once only. No idea on the validity, I need to contact the manufacturer. It's on the to do list)
8 - Don't start the scooter until the next day allowing the sealant to completely cure