Exhaust thread repair failed

[TRV8]

The exhaust thread repair that was done by the previous owner of my 1973 850 Norton failed. An aluminum insert was installed in the head then welded in place. The weld failed and the insert pulled out, one side only, Hopefully, you can see the photos in the Imgur link below.

When I cleaned things up, I found the fit between the insert and the head to be very loose. The carbon deposits in that area on my initial disassembly indicates that. I would have thought to be a press fit.

Now where to go from here? I've contacted James Comstock, but I don’t believe his usual process of repair will apply here, that is, installing a brass insert. Can anyone suggest alternatives?

Included are photos of the cleaned up exhaust port showing how little material is left in that area.

Any help would be greatly appreciated.
Regards,
Ken Hiebert


Right side, still intact:

 

[concours]

Engineering compromises leading to exhaust threads stripped (2012)

Best I can see is, the exhaust threads being a problem area, is the result of multiple engineering EVOLUTION compromises. In the beginning, the head was cast iron and the threaded attachments probably worked just fine. Then the thread (head) material changed to softer aluminum... and they...

www.accessnorton.com

Have a talented professional do it IN-SITU. I welded mine myself, still working great 40,000 miles later.

 

[mean gene]

That's ugly!!!

 

[kommando]

You need a better welder, plus it should be welded both inside and outside on a new insert with a good fit.

 

[Tornado]

i sent my 850 head to this guy in Ottawa for exhaust port threaded inserts:
precisioncyclecanada@gmail.com

He may be able to advise you.

 

[cliffa]

I hate to say it, but going by that picture that looks like it's past repair. The original port seems to have been opened out far larger than necessary, and there is no meat left to weld to, or to install a threaded insert. I hope I'm wrong.

The good news is that new (far) superior heads are available ( although there may be a wait as the first batch sold out pretty quickly).

STS / Fullauto Head

This is the 'new' Fullauto head. A improved version of the original stopped being produced several years ago. While the 1st generation heads were great, this new one is improved in several areas from the very core and up. Made in newly designed core boxes to ensure an unsurpassed quality...

coloradonortonworks.net

 

[B+Bogus]

I had the same issue with my first 850. I local engineering firm with lots of experience repairing the Lancashire Constabulary bikes manufactured custom bronze threaded inserts and screwed them in.
No good for you across the Pond, but gives you an idea of what's possible.
Not a fan of welded in inserts - just my view

 

[dobba99]

I also am not a fan of the welded in insert, seen too many pulled out. Try these guys EMP Tooling Services http://www.e-m-p.biz/
EMP Tooling
Unit 1
4 Solent Road
Havant
Hampshire
PO9 1JH
I'm sure they will be able to build up and machine new exhaust threads for you.

 

[concours]

I would offer that, the horrid snots shown in the OP's image are the work of a laymen. Failure is not surprising.
Properly done, by a professional, sound, lasting repairs are possible and there are thousands of examples in service.
Like "electrickery", those who do not understand the science involved are fearful of it.

 

[kommando]

I have a Mick Hemmings welded in aluminium threaded insert from the 90's still 100%, it replaced a shrunk in bronze insert that turned and then came out. Its more to do with who did the repair than the type of repair.

Seager Engineering

www.seager-engineering.com

NORTON COMMANDO EXHAUST PORT THREAD REPAIR SERVICE | eBay

NORTON TWIN EXHAUST. Using our own CNC Milling machine we helical interpolate a new thread into the exhaust port to accept one of our CNC MACHINED bronze inserts.The new thread is then CNC milled inside to fit the new rose nut exactly.

www.ebay.co.uk

 

[mdt-son]

You need a better welder, plus it should be welded both inside and outside on a new insert with a good fit.

+1
You need a thick oversize aluminum sleeve with a stepped ID due to the thread cutting operation.

The previous machined / drilled bore needs to be cleaned up. If it broke through the head casting, that location needs to be welded, possibly from both sides. You may end up with a substantial welding repair.

Prepare bore and sleeve for an interference fit as was done to Gortnipper 's cylinder head:

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

JC is the best but really backed up

www.accessnorton.com

Heat the cylinder head to 150 degrees C (302 deg F) and cool the sleeve to -70 deg C (-94 deg F) or lower temperature using "dry ice" (frozen CO2) or liquid nitrogen.

After fitting, secure the interference fitted sleeve by an external circumferential weld to obtain a sealed connection. This may be more elegant than in Gortnipper's case by chamfering the sleeve OD, achieving a recessed V-weld seam. Now you have the option of machining the ID and cutting the threads in aluminum, or machine the sleeve for a brass insert.

- Knut

 

[cjandme]

I saw a you tube clip "shed racing" I think it was.... Where by this fella had an aluminum head from a 1926 car, laser welded. It buit up a very large portion that was missing without warping as would have happened if it was built up with a conventional approach. So... Depending upon how expensive it is, it might be possible to have it built up and new threads cut.

 

[lazyeye6]

This isn't Cuba. New parts are available to keep our vintage machines running, though I appreciate those fundamentalists who
have the skills to fix the unfixable.

 

[MexicoMike]

I wouldn't give that a 2nd look: I'd buy a replacement head.

 

[gortnipper]

This is my old RH10 head. My friend was an aircraft tool maker for Boeing in Seattle, so he bored out the header cups that the PO had stripped out and made some custom inserts from aircraft aluminium and chamfered the outside edge of the insert and the inside of the head cups and pressed them in.

I had them welded in by the guys at Dewey’s Cycle. We talked about machining the weld flush again, but decided to leave it as the welds are largely hidden by the rose nuts.

My friend then cut the threads.

Still in since early 90s. But I am using a FA head these last few years.

 

[kommando]

This is my old RH10 head. My friend was an aircraft tool maker for Boeing in Seattle, so he bored out the header cups that the PO had stripped out and made some custom inserts from aircraft aluminium and chamfered the outside edge of the insert and the inside of the head cups and pressed them in.

I had them welded in by the guys at Dewey’s Cycle. We talked about machining the weld flush again, but decided to leave it as the welds are largely hidden by the rose nuts.

My friend then cut the threads.

Still in since early 90s. But I am using a FA head these last few years.

View attachment 85122

The Mick Hemmings welding is exactly the same, good penetration with no porosity.

 

[Dan1950]

This is my old RH10 head. My friend was an aircraft tool maker for Boeing in Seattle, so he bored out the header cups that the PO had stripped out and made some custom inserts from aircraft aluminium and chamfered the outside edge of the insert and the inside of the head cups and pressed them in.





View attachment 85122

So many fail to provide a bevel for penetration.

 

[marshg246]

This is my old RH10 head. My friend was an aircraft tool maker for Boeing in Seattle, so he bored out the header cups that the PO had stripped out and made some custom inserts from aircraft aluminium and chamfered the outside edge of the insert and the inside of the head cups and pressed them in.

I had them welded in by the guys at Dewey’s Cycle. We talked about machining the weld flush again, but decided to leave it as the welds are largely hidden by the rose nuts.

My friend then cut the threads.

Still in since early 90s. But I am using a FA head these last few years.

View attachment 85122

I had a head that both ports looked like that but were stripped. Sent it to Jim Comstock. Came back with his inserts and the old mess milled away - beautiful.

 

[gortnipper]

I had a head that both ports looked like that but were stripped. Sent it to Jim Comstock. Came back with his inserts and the old mess milled away - beautiful.

Yeah, that would be a future option for this head if it needed it. My friend Denis is a great machinist, so hopefully wont need it.

 

[Jdub]

OT: Loved Dewey's and Poke's as well down the street. Steve G is now down in Arizona if I recall correctly. Marsha was quite a character - had a real menthol accent to her voice.