AJS & Matchless Owners Club

All

My slightly modified 1949 G80 is on the road. The engine is standard and I have a chromed exhaust from Armours. I had the exhaust sleeved little to fit tighter into the head, and have two brackets fixing the exhaust to the frame. When cold the exhaust is very snug. When hot, I keep seeing the exhaust slip out a little.

Looking at the 1949 G80s, I can't see any additional fixings or clamps near the head to stop the exhaust moving around. There's no clamps up near the head at all.

Just looking to see if this is a problem that's been solved before I apply by brain to it. Note, exhaust has been swapped since this photo, but the problem existed on the original exhaust as well. Thanks in advance for any advice or guidance.

Now there's a bike with attitude. Looks great . Can't offer any suggestions to help, sorry.

Steve

Nice bike!

Doesn't the exhaust joint just gum up after a bit of use? Mine leaked a little after the rebuild, but it's fine now...

Looks nice. I know on my bikes the exhausts can be a bit loose so some exhaust silicone is applied. Also (not sure how rigid's work but on a sprung frame you would also have a bracket holding the silencer on. I usually have to position these so that the front and rear exhaust brackets are helping to pull the exhaust into the head (if that makes sense) and stay nice and solid (ish). Could a second bracket be attached?

One of the modifications on your bike is the fitting of an alloy head instead of the 49 iron head. No problem except the if a pipe was loose it will chatter in the head causing the alloy to wear and the pipe to become looser. It's unlikely that you will stop the pipe coming forward when hot by playing around with the brackets. (Been there tried that). You could try silicon but far better well out the end of your pipe. The usual advice is to use a hard wood cone and hammer it into the pipe. I have one made of steel. I have also achieved it using an old rear spindle inserted about a third of the way into the pipe and rotated a lot of times. The aim is the well out the very end of the pipe so it's a tight fit. You should then be able to stop the pipe moving with the brackets and not need any goo.

Have you considered a bead of RTV to seal it?

I tried different grades of silicone sealant including some that were marketed as 'high temperature'. After leaving them for a couple of days to cure, not one of them lasted more than a few minutes before it burned and blew out. I seal mine now with some 'stuff' that was supplied with a new after market exhaust for a big Japanese bike belonging to a friend. It's orange but has no makers name on the plain tube. That works perfectly and stayed put after leaving it for a couple of days to harden. It also probably helps that I've got a finned cooling ring on the pipe pushed right up against the head.

Pharisee wrote:I tried different grades of silicone sealant including some that were marketed as 'high temperature'. After leaving them for a couple of days to cure, not one of them lasted more than a few minutes before it burned and blew out. I seal mine now with some 'stuff' that was supplied with a new after market exhaust for a big Japanese bike belonging to a friend. It's orange but has no makers name on the plain tube. That works perfectly and stayed put after leaving it for a couple of days to harden. It also probably helps that I've got a finned cooling ring on the pipe pushed right up against the head.

DSC_2269-s.jpg

Pentex ultracopper rtv should be good for up to 371C. I've used it successfully on many exhaust systems, that said, I like Clive's idea to bell out the pipe to improve the fit. You could do this and cold shrink the header and slip it into the head. The interference fit will probably require a mallet to remove.

Hi

I've used Dow Corning 736 in many high temperature situations very successfully in the past, it's good to 315 C.

I've also checked the temperature of my head immediately after shutting down from 10 minutes running at 55 MPH at an air temperature of 23 C - it was at 218 C.

Regards Mick

Mick D wrote:Hi

I've used Dow Corning 736 in many high temperature situations very successfully in the past, it's good to 315 C.

I've also checked the temperature of my head immediately after shutting down from 10 minutes running at 55 MPH at an air temperature of 23 C - it was at 218 C.

Regards Mick

It's not the head temperature that's the problem. If there's the smallest gap, the hot exhaust gas will find it and that is way over 315°C. It's the temperature and the pressure of the hot gas that destroys the silicone sealant.