does anyone else do the exhaust repair like jim Comstock or is he the only one

Status
Not open for further replies.
seattle##gs said:
JC is the best but really backed up
Click to expand...
Can you get a set of inserts off him and have the work done.locally?

A mate of mine was a aircraft toolmaker and worked on Michigan St in Georgetown, and he machined out the ports and made some aluminum inserts that he interference fit in and then heliarc welded and cut the threads on his Bridgeport.

Saved my RH10 in the early 90s from the ham fisted PO.

does anyone else do the exhaust repair like jim Comstock or is he the only one


Actually, Steve @ Dewey’s did the welding.
 
I know how to do it just got to get the right pitch for my lathe or spend the money to buy the tap, $300 for the right tap, but so far my threads are still good and my motor is hard mounted in the Featherbed since the 80s, I saved the exhaust thread on a Norton I was rebuilding the motor for a friend a few years ago, any good machinest can do it or get the inserts from Jim.
 
Im talking about the bronze inserts. This already has an aluminum insert that's pulling out.
 
If the original aluminum insert is a pressed fit, but pulling out, could you just have it welded, as per gortnipper above?
 
that was already attempted once, though the welding was poor. I would like to have it done right if possible
 
I think if my threads ever let go, I'll get 2 or 3 areas around the port filled with weld, then drill and tap them for studs and fit Japanese style flanges with half collars like these..

does anyone else do the exhaust repair like jim Comstock or is he the only one
 
seattle##gs said:
that was already attempted once, though the welding was poor. I would like to have it done right if possible
Click to expand...
My machinist cut a chamfer in the insert and an opposing one.on the head to take more weld.

Contact Jim and see if he will sell you a pair of his oversized inserts for use in previously done heads.
 
For those in Australia, Murray at Cyclecraft Engineering in Perth repairs exhaust ports using a screwed in bronze insert. I had my 650SS head done by Murray and it looks identical to the RH10 that I had Jim Comstock do a few years ago. Murray is also a top bloke to deal with.
 
Had mine moded about 40 years ago to fit BMW airhead exhaust rings. Seems to have lasted the distance. With the original 850 balance pipes.
 

Attachments

  • does anyone else do the exhaust repair like jim Comstock or is he the only one
    20210903_104615.jpg
    197.4 KB · Views: 202
  • does anyone else do the exhaust repair like jim Comstock or is he the only one
    20210903_104605.jpg
    191.1 KB · Views: 221
850cmndo said:
Clever.
Click to expand...
Thanks.

At the time in the late 1970s you were on your own really. So an engineering friend turned up steel inserts. From memory they are an interference fit with a grub screw locking them in place from underneath. I'm pretty sure the inserts are just interference not threaded in but it was 40 years ago so?‽? Then with simple collets and flanged late Mk 11 type header pipes they stay very firmly in place. No problems ever since.

Obvously not perfectly original but you have to know Commandos pretty well to pick it and back then the bike was transport not a show piece.
 
Last edited:
  • Like
Reactions: HRD
The screwed in insert is the way to go. Any other is prone to failure at some point. I've seen too many welded in inserts with broken welds to even consider it an effective long term repair.
After measuring up my Iathe (to make sure i could turn the head itself) I made an angle plate attachment to mount the head at the correct attitude on the lathes faceplate. Anyone trying this you need a minimum center height of 6.5" to revolve a commando head.
The photo is of a Model 19 head getting the screwed insert treatment, this entailed making another jig as the port center to head gasket face was a different height to the commando head but the machining technique is the same.
 
Mick Hemmings did mine, he bored out to a set size, inserted an internally threaded Aluminium insert which was welded in at the front, no sign of any movement since he did it in 1987. Suggest you get the old weld removed but then cut in deeper before rewelding so there is a thicker weld.
 
In the UK today, there is Seager, who also make a good stainless rose and special tool for it.

According to his site Steve Maney is still doing them and I suspect RGM have a source for it.

In France, I think Bruno Perlinski does them, not sure of any others.

I think if I need it done I make take a nostalgic trip!
241166911_571112250969999_7819407245317962989_n.jpg


I understand Norman White did this to someone's Rickman! I don't have a better picture.

The head I originally had in my Rickman was ex Thruxton short stroke and the exhaust fitting was done like this, so that it could fit in a works space frame. To complete the job for the space frame the fins were also machined at the sides. Not needed in the Rickman.

I got the 2 stubs and 6 small allen screws with the head. It worked really well, sealed with standard Norton steel rings. And the exhaust was easier to fit than my current one!
 
Last edited:
Its a bad design. The problem is the flange on the end of the pipe - it pounds the exhaust nut loose. Cut off the flange and press or thread a tube into the head that fits the ex pipe. Or add a sleeve to the pipe so it fits the ID of the ex nut and hold the pipe in with a spring. My solution is below - the nuts are tightly screwed in until the threads bottom out (no exhaust rings). Silicone sealer on the exhaust nut threads for security and a collar on the ex pipe with a thin smear of silicone sealer on the collar OD. One thing I haven't tried is a slight taper on the collar. If you braze on the collar you must use phosphorus bronze.

does anyone else do the exhaust repair like jim Comstock or is he the only one
 
Last edited:
I would not know one reason why one could not weld exhaust stubs of correct material and interference fit in the exhaust ports.
In case someone could give me a clear explanation I would be more than interested.
Also if correct stub and filler material and welding procedure are given i can not see any danger for liquation cracking.

Kind regards
Christian
 
I had exactly the same issue - welded in alloy sleeves broken loose.
I'm in the UK, so not much help across the Pond, but for anyone interested I used David Burton Engineering in Thornton, Lancashire.
The bronze inserts were custom made to fit the larger holes, and it was a first class job.
Incidentally he just re-sleeved my 920 barrels as Steve Maney doesn't have any barrels or liners any more.
David used to do the exhaust repairs for the Lancashire Constabulary bikes....
 
Status
Not open for further replies.
Back
Top