Wanted: replacement exhaust thread insert for 3 1/2

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julianharty
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Wanted: replacement exhaust thread insert for 3 1/2

Post by julianharty »

I thought I'd try this request here rather than in one of the bike specific topics... I've a 3 1/2 Sport that came with phosphor bronze inserts for the exhaust ports. One of them exited onto the M40 motorway (together with the rear downpipe for the 2-1, the exhaust ring, etc.) This was near the end of a 250 mile trip and I'd actually discussed ways of securing it with Paul at Stafford Show, but it deserted me before I had chance to try any of the techniques we discussed. I recovered the now very dented downpipe and exhaust nut and will sort these separately.

I'd like a replacement insert and wondered if anyone here can make one for me please? I'm happy to pay for it, of course. dimensions are: 44 mm diameter, 22 mm deep with presumably a standard hole at the end of 24mm for the exhaust gasses from the head. I'm planning to use a combination of exhaust paste (since elsewhere on the forum there are examples of it holding on for grim death) and a small threaded grub screw lengthways between the head and the insert. Other suggestions are welcome.

BTW: The 2-1 exhaust seems to be handmade by a now defunct small company called gazelle in Wales. It didn't have clamps to secure the downpipes, paradoxically the ones I'd ordered arrived yesterday too. And I also bought some exhaust springs and weld-on clips at Stafford Show. Ho hum, I'm still testing this old bike to see what else needs improving so it's able to do lots of miles without failure.
'It must be a .....'
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Joined: 12 Sep 2010 12:25

Re: Wanted: replacement exhaust thread insert for 3 1/2

Post by 'It must be a .....' »

Gazelle Exhausts (Neimann Brausch) moved to Ruffec in France, but I don't know if they are still trading as it was a few years back.
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Ming
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Re: Wanted: replacement exhaust thread insert for 3 1/2

Post by Ming »

'It must be a .....' wrote:Gazelle Exhausts (Neimann Brausch) moved to Ruffec in France, but I don't know if they are still trading as it was a few years back.
Looks like they're still trading - but not in exhaust systems...
harrymuffin
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Re: Wanted: replacement exhaust thread insert for 3 1/2

Post by harrymuffin »

I have just made a S.S 2-1 with silencer for a chap and I used to make the exhaust nuts in PB. The effort in obtaining the hollow bored bar out weighs the cost of manufacture for other people and solid bar is expensive anyway. I can let you have a front pipe in SS to match your rear pipe of which I have a number of spares in 350 and 500 form. When you fit the systems back to the bike then drill a hole in the nut and in the fin close to the port and lock wire so the nut does not undo. You can get away with out drilling the nut by hooking the loop over the castellation and lock wiring from the head end. I would not advise locking the nuts in with grub screws as depending on how ham fisted you are, you may damage the thread on the nut and have difficulty getting it undone. If you use 2-1 then have collars brazed to the end that goes into the head and do away with the collets, the nuts engaging with the collars to effect a gas seal with the gas rings.
julianharty
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Re: Wanted: replacement exhaust thread insert for 3 1/2

Post by julianharty »

Harry,
Thanks for offering a front downpipe. What I really need is to replace the previous PB insert IN THE HEAD. [A new 2 into 1 would be great and something we can follow up on separately.] The previous PB insert was an interference fit in the head, and the interference wasn't enough in this case as it came out of the head complete with the nut (which I still have) and the rear downpipe. The idea of the pin/grub screw wasn't to hold the exhaust NUT, it was to hold the INSERT in place. It'd go lengthwise between the outer diameter of the insert and the head by drilling in a small hole. A bit like a woodruff key stops something from turning on a shaft. Sorry I don't have the precise term for what I'm trying to explain. I can tell I've not been sufficiently clear from the answers I've received so far :)

In terms of my exhaust, I managed to find the downpipe with the exhaust nut, but it's partly squashed so I've currently cut off the damaged section and will experiment with flexible 32mm S/S exhaust piping between it and the 2-1 collector. It looks like it could work quite well and act as a template if/when I want to have a new replacement rear downpipe.

BTW: Many years ago (around 1985) I had a ratty Strada where I ended up making a flange on the downpipes that I held in with 2 bolts into the head. So if I don't find a way to replace the thread in the head (which is what the PB insert provided) I guess I could make up an enlarged collar and use springs or similar to hold the downpipe in place on the head.
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Ming
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Re: Wanted: replacement exhaust thread insert for 3 1/2

Post by Ming »

You are probably aware that NLM can provide a thread replacement service for the exhaust port and I'm sure that Paul Compton has mentioned the use of a grub-screw 'key' in that position, too.
julianharty
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Re: Wanted: replacement exhaust thread insert for 3 1/2

Post by julianharty »

Ming,
You're right on both accounts. I spoke to Rob at NLM yesterday, they charge £95 + VAT to weld in an aluminium replacement. He recommends allowing a couple of weeks for them to do this given their current workload. This will be the route I'll take if I don't find an option I prefer. Fortunately I'd recently bought a pair of heads in very good overall condition (apart from a damaged exhaust valve on one) from the USA so I've got time to address this without needing to rush to get the bike back on the road.

And yes Paul was who suggested the pinning technique. If I could find the insert that fell out I'd glue it back in with exhaust paste and pin it and get on with riding the bike :) For now, I'm fitting one of the heads I bought, and just waiting for a new inlet insert to arrive from NLM later today (the heads didn't have these and the one in my current head doesn't want to leave it, unlike the exhaust insert which left too easily.

To be clear, I'd still like help to create and fit a PB insert to the current head. Thanks to everyone's suggestions already and for any to come.
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