Trouble getting Downpipe>Cat joint sealed

[AllHailKingVolvo]

Hi all,
I fitted a new Lambda sensor today, but the old one was so badly rusted into place I had to remove the cat and use a very lengthy breaker bar to get it to shift.

New Lambda is in, car runs fine, except for the fact that the cat>downpipe joint is blowing. It has the two swaged flange sections with the sealing ring between them, all surfaces were slightly pitted and rusty but were sealing just fine before I dismantled it.

Does anyone have any tips on how to get it to seal nicely again? Or am i looking at a new cat and downpipe to get a clean seal?

[Laird Scooby]

Originally Posted by AllHailKingVolvo

Hi all,
I fitted a new Lambda sensor today, but the old one was so badly rusted into place I had to remove the cat and use a very lengthy breaker bar to get it to shift.

New Lambda is in, car runs fine, except for the fact that the cat>downpipe joint is blowing. It has the two swaged flange sections with the sealing ring between them, all surfaces were slightly pitted and rusty but were sealing just fine before I dismantled it.

Does anyone have any tips on how to get it to seal nicely again? Or am i looking at a new cat and downpipe to get a clean seal?

Rotary wire brush in a drill on the mating faces, new gasket and thin smear of copper grease Phil.

Tighten it finger tight only before starting the engine, let it run up to temperature, tightening gently and evenly on the clamp until the blow stops.

Don't be tempted to use any form of exhaust sealant - it can easily clog the cat! Usually though, clean the mating faces up and a new sealing ring all smeared lightly with copper grease does the job.

I hope you smeared some copper grease on the threads of the new Lambda sensor so you don't have this palaver again!

[AllHailKingVolvo]

Thanks Dave! Will sort that this coming week.

The Lambda was a Bosch unit and came pre-greased with copper grease and a neat plastic cap over the threads and sensor! Very good thinking of them.

[Stephen Edwin]

I was slow discovering copper based grease Dave. About 1970. That tin of the stuff has gone manky now. (Technical term?) But the current tin of the stuff is always ready to hand.

Castrol red grease, vegetable based, is also useful. Can still be got from e.g. eBay. For use with rubber. I always use it with cooling system hoses. (There is a reason why Durex do not recommend petroleum jelly lubricants.)

[Laird Scooby]

Originally Posted by AllHailKingVolvo

Thanks Dave! Will sort that this coming week.

The Lambda was a Bosch unit and came pre-greased with copper grease and a neat plastic cap over the threads and sensor! Very good thinking of them.

The protective cap is a common fit to all replacement Lambdas Phil and usually some sort of anti-seize compound on the threads, whether it's copper or graphite grease or something similar.

Never enough of it though!

You might find the blow seals itself as you use the car and soot gets into the gaps, meanwhile the blow might cause a little rough running as technically you've got an air leak upstream of the Lambda sensor so as well as letting exhaust gases out, it's pulling air in.

Originally Posted by Stephen Edwin

I was slow discovering copper based grease Dave. About 1970. That tin of the stuff has gone manky now. (Technical term?) But the current tin of the stuff is always ready to hand.

Castrol red grease, vegetable based, is also useful. Can still be got from e.g. eBay. For use with rubber. I always use it with cooling system hoses. (There is a reason why Durex do not recommend petroleum jelly lubricants.)

You'll probably find you can scrape the manky layer off the top of the grease Stephen - saves buying a new tin if so!

As for suitable lubricants for latex products - not very many! Silicone oil will cause the latex to deform and swell losing its elasticity, long time since i've done anything with latex (about 25 years ago) but i know we had to use a water-based lube to preserve its integrity.

Quite important when the latex products in question were small balloons as part of a bleed valve assembly as a pressure control for peristaltic and similar medical garments for preventing bed sores, DVT and other nasty things for patients with limited/restricted movement.

[TonyS9]

Thats the flanged clamped joint?
The clamp normally rusts to death, how is yours. My 'fix' was to fit a custom stainless system from the Turbo back including new cat, although its fairly cheap and easy to fit (weld) a new sleeved joint or, more difficultly, to remake the original.

The clamp is captured on the down pipe and cat and cannot be removed, also pretty much impossible to source except for a 3 piece job, which seem rediculously expensive (£30 per side). According to my experience it should be possible to get this laser cut for a very small amount (like £2 per section).

[Laird Scooby]

This is the system i'm pretty sure he has Tony :



The sealing ring is SBG5 in that diagram and is pretty generic throughout not just Volvo exhausts but many others as well.

If all else fails, the clamp rings can be removed by cutting the ends of the two pipes and joined using one of these :

https://www.ebay.co.uk/itm/Audi-100-...t/301941663929



I think 54mm is the right size, would be wise to measure first though! The clamp bolts need tightening evenly, a couple of turns at a time on each or the sleeve will distort and blow.

All that said, if the exhaust parts aren't rotten (Phil mentioned slight pitting on each so nothing to speak of really) a new sealing ring and some copper grease on the ring after cleaning the inside of the conical bits of pipe then progressively tighten the clamp bolts as it warms up usually sorts it.

[Stephen Edwin]

Originally Posted by Laird Scooby

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You'll probably find you can scrape the manky layer off the top of the grease Stephen - saves buying a new tin if so!

As for suitable lubricants for latex products - not very many!


.....

The manky layer can stay to seal the contents of the museum piece tin. And why risk trusting the stuff underneath. Yuk. I'm not spoiling the jam jar for a haporth of new grease.

Plenty of lube on supermarket shelves nowadays....and as you mention latex I guess the forum member whose grandfather invented the bicycle will know about lubricating latex.

....