Exhaust Exhaust Heat Sink Fix


Active Member
Local time
5:44 PM
Jan 31, 2008
South Australia
Here is a possible solution to prevent leaking exhaust due to expansion from heat

Motor bikes have fins on the exhaust pipes at the header/port section.

It was also suggested at a car exhaust place, to try a heat sink principle.

The way it seems to work is, heat causes the plate on the HT's exhaust pipe
header to warp.

If that heat is transfered away, then it may reduced the tendency of warping.

The way I've done a test is remove the HT exhaust studs, replaced with longer allen key bolts, filled the slack with spring washers and the HT's nut.

Spring washers may be an advantage over flat washers.
Not had any major leaks since, infact none.

Gasket is home made using exhaust gasket material from speed shop and it's cut to suit the engine's port shape and sealed with Stag.



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I've done the same except i didn't put springs between the bolt head and the nut :/

just gives a lot more surface area to transfer heat into the air and away from the exhaust flange/head.
I have done away with the spring washers to lately. But added some "looks", such as grinding hex nuts round to take up the space of the longer bolts, one flat washer and one spring washer.
Same result, the flange did not warp.
Keep checking for tightness after intitial runs for a few days. Eventually it will bottom out and stay tight.

Also the exhaust pipe flange was not entirely square. Used the side of the grinding wheel, a steel ruler put a cross to see if light shines through accros the flange and then carefully ground it flatter as best as, bit at a time and checking for flatness.
Once flat enough, then evenly grind acrosds the face of the flange/plate to give an even rough surface. Principle here is, ya do the same with tube patches, roughen it up a little so the glue sticks.

I did not use any gasket sealant incase I had to remove the pipe after initial starting which I did remove again in anycase to finally paint the pipe black if it all worked well.
Maybe this one was pure luck, but has not leaked while not using sealants.
I'll put some on though when it's finally all done.
I don't use silicon, it's either hard setting gasket paste, ( looks like Vegemite) or Stag Jointing Paste
Prefer Stag cos it cleans off easier


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one would imagine that stacking alternate diameter washers would create a pretty decent mini heatsink, and if you really want to get carried away put a TIM between them (thermal interface material, if you're a computer geek you might have a tube of artic silver or something floating around). It'd look pretty cool too, i would imagine, like a mini cylinder head on each bolt, haha.
yes eta, but the 'fins' created by the alternate side washers aren't facing the optimum direction for good airflow :/ but it would be better than none :D
ET: if you're a computer geek you might have a tube of artic silver or something floating around).

Nope, this is the old school tea and coffee drinkers method. (Not to be confused with age BTW)
The principle is to leave the metal spoon in the hot tea cup so it cools sooner. The heat from the hot liquid rises up the metal spoon because it's cooler. Surrounding temeperature does the rest.
It's the same as saving expensive glass ware when pouring hot liquids to avoid then cracking, have a metal spoon in place so to avoid damage.

Same wit the HT pipe flange, the heat has somewhere to escape, therefore avoiding the plate from warping.

Have a look as some cast iron exhaust manifold bolts on a car. They are never a tight fit, this to allow for expansion.
It is also common practice to face a exhaust manifold when replacing gaskets to have perfect flat surface. And while we on that subject, tighten from the centre-outwards. This is the same principle when ironing ya trousers, from center out.

It ain't rocket science, the HT was not made to go to the moon !
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To use your analogy, imagine a cup filled with hot leadshot balls and a teaspoon to disspate heat - pouring in water (even at the same temperature as the lead ballls) would increase the surface area to the spoon, and allow it to remove more heat. The water is acting as a TIM (thermal interface material). ANY joint will transfer more heat with a TIM. The alternate washer size stacking will increase surface area, and a TIM between them will allow more efficient heat transfer- but the TIM would be getting carried away.
hot leadshot balls and a teaspoon to disspate heat - pouring in water (even at the same temperature as the lead ballls)

That is an extreme cup of coffee !
yeah I understand the washer theory and it would probably work.
If you have a problem with your exhaust flange and it keeps leaking, then by all means try your washer method and post the results.
Make sure the exhaust pipe is secured with a strap, to prevent lateral movement. I used M6 coupler nuts, work mint, don't look too bad,
plain nuts can be doubled, or tripled, tighten flange up, add check nuts to keep flange nuts from backing out.