Exhaust sealing advice needed

The downtube to collector box on my CB400T leaked. New (non-original)
exhaust downtubes and collector box fitted by previous owner. I disassembled
the exhaust and found the previous owner had re-used the old fibre seals -
which were in pieces and would never seal again.

I bought new fibre seals - they are slightly too big to go into the
collector box and slightly too small to go over the downtubes. I've had a
bit of a bash at the collector box entry and can slip the seals in about
half way - they might tap in the rest of the way. I've filed a slight
chamfer on the inner edge of the seals but they don't look like they will
slip over the downtubes without a lot of bashing. I could have a go at
filing 0.25mm off their inner radius - but I'm not too keen on trying that.

These seals feel very fragile and I don't want to bash/tap them much. Any
advice?

If I manage to destroy them, what other method is there to seal the 3mm gap
in the join between the tube and the box?

John

 

They are.

You can buy a type of fabric tape that withstands high temperatures.
HVAC people sell them. A length of that rolled round the headers once,
maybe twice, and liberally slathered in exhaust gum will do the trick
once the clamps are tightened up.

 

Gentlemen

Thank you for that information - I will store it for future use.

What I did:

1. Used a JCB bucket pin (44.8mm diameter) to open the collector box inlet
hole up a little bit and ensure roundness.
2. Heated one of the inlet holes to cherry red and tapped a dink out of it.
Used the bucket pin again.
3. Used a half round file to clean said inlet holes - followed by tidying
with various grades of emery paper until the seal could just be pushed in.
4. Made a tubular fibre washer file with a broom handle and garnet paper.
5. Rubbed the fibre seals on the garnet paper for some time until they
slipped over the ends of the down pipes. (Use a brass brush as a pinning
tool for the garnet paper as you go).

It only took 2 hours.

The joys of making an older bike well again.

John

 

If these are the shiny, grey-coloured seals that Honda often use to seal
exhaust connections, you will probably find, on close inspection, that
they are made up from multiple layers compressed together. I have had
success in the past in separating and removing layers to create a thinner
gasket.

Alternatively...I have used Gun Gum Exhaust Repair Bandage successfully
for such jobs - wrapped around the smaller diameter pipe end before
insertion. Another approach - a metal shim can be made from Gun Gum
Flexiwrap Silencer Repair (or from an old tin can) to take up the slack
between pipes. Either of these ways alternative, together with a liberal
application of Gun Gum putty or similar exhaust paste, should do the trick.

 

You must have steadier hands than I. I've tried that dodge, but never
with any real success.

 

Me too. I've rasped down oversized gaskets, then applied a goodly
swipe of sealant to make up the grooves I've caused, but I've never
managed to peel one like an onion.

Of sealant: for permanent solutions - Hermetite (or similar) exhaust
assembly paste, as suggested by JB. Slicks the puipes, letting them
slide together, then goes hard with heat (either running the engine, as
intended - or if there's a really big gap and you're afeared of it
blowing bubbles, an externally-applied blowlamp will suffice) and sets
like concrete.

For joints you'll want to dismantle again, bathroom silicone sealant.
Really. Never goes really hard and won't work if there's any direct
pressure on it, but it seals 100% around the likes of header pipes,
doesn't look unsightly and comes apart once you've unbolted the thing,
with a sharp tug.

For the best of both worlds, a relatively recent discovery: Hilti
intumescent firestop mastic:

http://www.hilti.co.uk/holuk/page/module/product/prca_rangedetail.jsf;js
essionid=8A14EBAB917054B24AA64FAE57620239.node1?lang=en&nodeId=-85904

Sticks like shit to a blanket, swells up when the engine is run,
sealing absolutely gastight. Dismantles with a tug and a twist, cleans
off metal easily. Bit not cheap, but certainly does a job of work.

 

It is fiddlearse but doable.

Those with experience of carefully peeling a solitary ten bob note from
the roll without disturbing the rest will probably have more success
though.

 

I've met a few who could peel an orange in their pocket - such skill is
useful in other areas, without a doubt.

 

OK, I can easily imagine other activities that require finger
dexterity in a pocket, but for the life of me, I can't imagine why
anyone would need to peel an orange in a pocket. Or why this
particular skill would ever become public knowledge.

"Oh, I say. Did you know I can peel an orange in my pocket?"
"Get away from me, you fuckin' pervert!"

 

It's a byword, an analogy, for being so tight with anything they need a
crowbar to have a shit.

 

Similar to "An arsehole so tight only a dog can hear them fart" ?