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For All You Petrol Heads

Bolts & Gaskets

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Adrian Smith 128/03/2015 13:39:38
2267 forum posts
1002 photos

I have had limited success in ensuring that muffler bolts don't unwind on petrol engines.

What doesn't work, and I've tried believe me, is any sort of thread locker be it blue (medium) or red(permanent?). Because as soon as heat gets to work that joint fails. I have tried to negate the effects of vibration and also balancing the prop, but it is still an issue. The only thing that seems to work is smearing the bolt threads with Holt's Automotive Gun Gum (used on exhausts). However, when you want to dismantle the set up is is rather a difficult job. What do you guys use?

I have also experimented with a sheet of automotive gasket material, but I find it very quickly burns away. I am also not sure if heat resistant liquid gasket will be much better. Any ideas?

Steve Hargreaves - Moderator28/03/2015 14:05:09
6720 forum posts
189 photos

No direct experience Adrian but I think you are right about threadlock....thats going to fall over well before you get to 200C & I would thing a petrol exhaust is gong to exceed that by some margin.....!! I do wonder id a wrap or two of PTFE tape (plumbers tape) over the thread before fitting them to the engine might hold them. PTFE is good up to about 300-350C. Failing that we are looking at a mechanical method so spring washers or serrated washers under the heads might help. It's probably worth seeking out the correct torque figure for the size of bolt you have & tightening it up to this figure (assuming you have a torque wrench that will cover these values) it's surprising sometimes how much torque a bolt will actually take....

For gasket material then yes you will need something a bit special....I approached a gasket manufacturer I found on Google & asked them for some offcuts...they sent me a piece about 10" square rated at 450C & I use this on my petrol EVO10 where it has worked flawlessly....

Good luck...

Cuban828/03/2015 14:06:38
2725 forum posts
13 photos

One of the many different types of lock washer perhaps?

ben goodfellow 128/03/2015 15:03:35
1069 forum posts
41 photos

NORD lock washers from model fixings ???

TheFlyingCrust28/03/2015 15:47:05
611 forum posts
67 photos

Many Silicon sealants are rated to 250 deg C. Check on the tube before using. I've used the stuff to temporarily repair car silencer boxes the have developed a leak. Smeared on a bit of tin can and wired in place.

Also works well as a gasket for glow motor exhausts. Petrol motors may be a bit too hot on this joint.

I've used it for thread lock but not at temperature.

Steve, standard plumbers PTFE tape only has about 5% PTFE. I don't know if it'd hold at temp.

Adrian, are the screw heads on your motor big enough to drill and wire? Or file a flat on and use tab washers?


john stones 128/03/2015 18:05:01
10605 forum posts
1480 photos

Never had much trouble myself Adrian and the only lad who I know that has had problems, had an OS 33 in a lightly built Sebart Sukhoi, it chucked exhaust and standoff bolts non stop and he was using same threadlocks as the rest of us ? Can you mount on some sort of soft mount or damp vibration somehow at the mounting point.


Adrian Smith 128/03/2015 20:52:25
2267 forum posts
1002 photos

Funnily enough John the engine I am have trouble with is an os 33 gt. It keeps throwing a bolt from the muffler. The bolts are the standard stuff os provides M5 with an Allen key head.

john stones 128/03/2015 20:57:53
10605 forum posts
1480 photos

The gent flys at another club now Adrian, I will send him a p.m see what he says


john stones 128/03/2015 21:14:01
10605 forum posts
1480 photos

Right he says make very sure the prop is balanced and these sorted his


reg shaw28/03/2015 21:45:27
638 forum posts
562 photos

Have you tried running the engine then when warm nip the bolts up a bit. You could also cross drill the heads and wire lock the bolts together but I've never had to go to those lengths but I know some that do.


Adrian Smith 128/03/2015 23:00:43
2267 forum posts
1002 photos

Those Nordlock washers seem to be the real deal John. I need some other bits from ModelFixings so I'll give it a try. I must admit Reg I have tried the old warm and nip trick, but doesn't seem to work. I didn't really want to go to the extreme lengths cross drilling the threads and wire lock the bolts together. One to bear in mind though, however. Thanks guys for all your suggestions.

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