g3l exhaust

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r wheat
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Re: g3l exhaust

Post by r wheat »

Hi taking this a little further the dimensions of the piece sticking out of the head od 1 5/8" bore 1 3/8" length 3/4" I would assume the pipe goes over the outside but what would have held it in place, the last answer was quite brilliant as to all the possibilities, I shall check to see if there are any numbers on the head and the barrel. thanks again for all the replies cheers Richard
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Rob Harknett
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Re: g3l exhaust

Post by Rob Harknett »

The exhaust pipe fitted on the exhaust spigot. So you would need 1 5/8" I/S dia pipe. The pipe should have slit cut in the underside, just a little shallow than the length of the spigot. So just a little less than 3/4". This allows the pipe to open a little, to give clearance to fit. The pipe should go on easy. If not make sure it is very clean, so the pipe does fit easy. Any force will result in breaking the brittle cast spigot. The pipe has an exhaust cooling ring clamp to nip it up on the spigot. Just nipped up. Again, any force could crack the spigot. The pipe will need a silencer with an I/S dia to take the O/A dia of the pipe. This too will have a split, so it will open a little to accept the pipe, which is secured with a C clip. There will also be a bracket to hold the pipe. Some pipes have a stud on them, the position being critical. So it may be a good idea to forget about having a stud on the pipe. Just fashion an L bracket. The bottom leg should bolt on a frame bolt. You will then need a C clip on the pipe, to bolt onto the long leg of the bracket. Needless to say, the C clip on the pipe, will have a smaller I/S dia than that on the silencer. The spigot & pipe dimensions you have are the same as on late 1930's AJS. Probably same as Matchless, which I have less knowledge of.
You may wonder why the engine number does not seem to be within known WD contracts. One thing I can think of is, it was assembled with odds and sods available to make a machine. To be used by the many " home " gov. depts. that needed bikes on the home front. Like despatch riders that went round towns to report air raid damage. A.T.S women despatch riders etc. It would make sense using up old stock bits for such non standard part bikes. So to keep military bikes standard spec.
Bit of Plumstead history: During war time, if there was any bombing in the factory area, a member of staff would ride round checking on workers homes. This is all documented in a book I call Johns book. Memories of Plumsread. The memories I got from John and Rose Rourke, John started work at Plumstead in 1928. Worth a read, you will find it here . http://www.jampot.com/article_read.asp?id=570
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clive
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Re: g3l exhaust

Post by clive »

when I had my 49 G80 the pipe fitted over without a slit and I used exhaust paste to seal it. I would use a pipe with a stud and fashion your own bracket. Make sure the rear mount for the silencer to the frame is as short as possible and the joint to the pipe is tightly clamped. What you want to avoid is any possibility for the whole thing to "waggle" under vibration as this will put that spigot at risk.
clive
if it ain't broke don't fix
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Rob Harknett
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Re: g3l exhaust

Post by Rob Harknett »

Ashampoo_Snap_2017.08.05_10h10m15s_001_.png
This illustrates the prewar exhaust system for AJS, Matchless would have been similar. Note it has all C clip fittings. The cooling ring clamp ( not shown ) for pipe to spigot is also like a C clip. Matchless was a different design of cooling ring to AJS. Many of the prewar machines were twin port. So pipes would be handed. As the silencer has no stud, it will fit left or right side. The picture shows silencer fittings for low and upsweep pipes. Without a stud , a silencer would fit many different marques. All screwed fittings can be replaced if damaged. Some post war machines have a stud welded on the pipe, some a welded on bracket. Of the two, I would prefer the bracket, if I had the choice. Studs on pipes get threads damaged. Even if removed, with some difficulty, due to heat and rust, the threads get worn and no longer hold fast. You can only easily replace the nut. This problem does not happen with C clip fittings. Studs can also break off pipes and silencers. I have also had to replace pipes and silencers, due to rust at the stud or bracket, shortening the life of these more expensive parts. In fact, I have a prewar and post war machine, both restored at the same time. The prewar bike exhaust system is still sound with all its C clip fittings. The post war machine is on it's second pipe and third silencer. Silencer replaced twice due to rust around the welded on bracket causing it to blow. This is not to try and prove Clive is wrong in recommending studs. I respect his very knowledgeable comments. So it is up to others, if given the choice of different opinions, to decide which way they may choose to go. Even the designers at AMC moved away from C clips to welded on studs and brackets. Cost cutting ? making parts AMC only? More modern appearance? Time saving ?
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r wheat
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Re: g3l exhaust

Post by r wheat »

Hi well thanks for every thing could not have wished for more info, I have not found any numbers on the head at all, the head has 9 fins I wondered if post war heads have the same amount as all post war heads I have seen have a smaller number, to fit this head the exhaust pipe would need to be 1 3/4" od or have a flange at the head end, does any one know which would be correct all the best Richard
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clive
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Re: g3l exhaust

Post by clive »

not sure what you were trying to show with the last picture but you appear to have the rubber gasket and top flat steel washer on one side and the top washer, rubber gasket and angled steel washer on the other side still in place in the pushrod tube holes. So make sure you fit new rubbers and find the missing angled washer.
Rob the thing the c clamp will not do I suspect is help the pipe stay in the head fitting, whereas the stud will act as a more firm base. Having said that I have to agree with your analysis since I just had one fracture away from where it was welded to the pipe on the return from Poland!
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Rob Harknett
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Re: g3l exhaust

Post by Rob Harknett »

I thought I covered pipe size earlier. It needs an I/S dia. to fit the spigot O/S dia.
The exhaust pipe fitted on the exhaust spigot. So you would need 1 5/8" I/S dia pipe. The pipe should have slit cut in the underside, just a little shallow than the length of the spigot. The split allows the pipe to open out a bit. I also allows the cooling ring clamp to tighten the pipe on the spigot. The same way the split in the silencer allows the silencer to tighten on the pipe.
Getting a 1 3/4" O/S does not guarantee the !/S will fit.
Clive, I have never had a pipe move, clamped on the spigot with a cooling ring. The slit allows it to tighten on, same as the silencer will tighten on the pipe the other end.. In fact quite the opposite, a pipe is even a job to get off, once gummed up with carbon. So the C clip on the pipe has little to do except give support to hold the pipe level. Unlike a post war machine where the pipe just pushes in the head. There is nothing but the bottom bracket fitting to help keep the pipe in the head. A stud may be better for that system. Although at some point in the fitting there is usually a slot instead of a hole, to give some tolerance. If that fitting loosens, the pipe could rattle in the head.
r wheat
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Re: g3l exhaust

Post by r wheat »

Hi thanks for all your help cheers Richard
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