documentary- exhaust thread repair

[comnoz]

What do you do when the welded in insert comes out. Here's the insert , you can see the narrow ring of weld that held it.

It left a hole to big to thread or do much with except weld

So after an afternoon of weld a little and let it cool you end up with aluminum were ther was none.

boring and facing off the excess

Then comes a big custom tap

And the hole is ready for a hard bronz insert

A little heat and the hole gets large enough to install the insert with a little JB weld for insurance

It goes in tight

A little cleanup and it's fixed forever

 

[Scruff]

Comnoz I just love your work. Wish i had the alluminium welding gear at home. I like to do all my own repairs but some things like alluminium welding I have to farm out.
Ian

 

[swooshdave]

Why JB over Loctite?

 

[comnoz]

JB weld because the insert is an interference fit and locktite tends to sieze up before the insert is tightened in a hot head. When I first started doing them many years ago I was not using an interferance fit and was just installing them cold with red high temp locktite. I found after they had been used for a while the locktite was no longer holding them in place so they would sometimes unscrew with the exhaust nut on dissassembly.

 

[GavinJuice]

JB weld because the insert is an interference fit and locktite tends to sieze up before the insert is tightened in a hot head.

I don't understand this statement??

 

[BrianK]

Nor I. But I have to think this is a high enough temperature application that red loctite is NOT going to hold at all. JB Weld sounds a bit extreme, but ...without having given it a lot of thought...perhaps that's exactly what's called for here?

 

[Jeandr]

Jim, if you do it too good, they won't fail and you will be out of work :lol:

Very interesting to see it done that way, did you make the tap yourself? Do you recomend the stock steel exhaust nuts or brass ones with brass inserts?

I am always in awe of good machinists, no exception here.

Jean

 

[comnoz]

Wit stock aluminum threads there is probably a small advantage in using the bronze nuts because they expand at a rate similar to the aluminum head so they tend to stay tighter. With the bronze inserts I would stay with steel nuts to avoid the friction caused when like metals rub against each another.
An interferance fit means the insert is slightly larger than the hole it is being screwed into when they are at the same temperature. To make it fit I heat the head and cool the insert before I thread them together. Locktight sets up very fast when it gets hot . Sometimes faster than I could screw the insert into the hole. Then I ended up having to bore out a half installed insert that wouldn't move anymore and starting over. There is no such thing as overkill when it comes to keeping an exhaust attached to a Norton head. Jim

 

[GavinJuice]

AH, so it was the tight clearance and quick lack of oxygen that was setting up it too quick. Something to keep in mind...

 

[seaguy]

Thanks for the pictorial demo comnoz. Would you mind posting your "Shingle" for some of us new guys that don't know what and where everything availiable can be found yet?

 

[maylar]

Beautiful work. You're a talented dude.

Let me ask, what mechanism do you use to get the bores at the correct angle? The Mark 1 Eyeball, or do you have a jig? Reason I ask is that I had the threads repaired on my 850 years ago and when I reassembled the motor the stock 850 crossover exhaust would not line up. The right side port was machined slightly off and with the crossover pipe in place the right headpipe wouldn't mate with its muffler. Not a big deal for me to use 750 pipes, but it could annoy someone trying to keep a machine original.

 

[comnoz]

As far as a shingle I may eventually get a website but right now bussiness has been good without paying the extra expense. You can e-mail me at comnoz2@juno.com or PM me at the above address. My shop phone is 719-646-2610 and I am always willing to talk about Norton stuff. I am just one "retired" guy working in a shop behind my house so things don't always happen in as timely a fashion as I would like, but I like to think when it's done it's done right. My biggest customer is Colorado Norton Works so you can access most of my stuff from them also. Jim


The boring and threading for the exhaust threads are done on a Bridgport mill with a jig to hold the head at the right angle. Not suprisingly the angle of the original exhaust outlet varied from head to head but when I get done they are all at an angle that seemed to be an average of what came out of the factory. Jim

 

[seaguy]

Jim ,since you have seen many Norton 750 heads I have a question. I have noticed that the cylinder mating surface of my head is barely a 16" higher than the fins. Is that typical ? I was wondering if it has been milled a lot.

 

[comnoz]

A sixteenth inch sounds pretty common. Combat heads were milled almost to the first fin.

 

[Rob94010]

Beautiful work. Simply beautiful. :shock:

 

[Foxy]

TOP THREAD JIM ! Great to see a perfectionist work. You cant beat pictures. I also like the photo elsewhere of you and your black, non carbed Norton. It put a face to all the other interesting post made, its a pitty that everyone doesnt state which part of the world they live in as I find this interesting aswell. Keep up the good work as its guys like you that make this forum and Nortons so interesting (edjamacational!). Regards Foxy

 

[plj850]

Beautiful work. Simply beautiful. :shock:

Yes great to see such skill and care in the world of break and throw away...

 

[comnoz]

The links are fixed now.
Since this doc. I have started cutting the inserts and all the threads with the CNC machine and a thread mill. They all come out perfect and identical now. Jim

 

[Rich_j]

Wit stock aluminum threads there is probably a small advantage in using the bronze nuts because they expand at a rate similar to the aluminum head so they tend to stay tighter. With the bronze inserts I would stay with steel nuts to avoid the friction caused when like metals rub against each another.
An interferance fit means the insert is slightly larger than the hole it is being screwed into when they are at the same temperature. To make it fit I heat the head and cool the insert before I thread them together. Locktight sets up very fast when it gets hot . Sometimes faster than I could screw the insert into the hole. Then I ended up having to bore out a half installed insert that wouldn't move anymore and starting over. There is no such thing as overkill when it comes to keeping an exhaust attached to a Norton head. Jim

Is there a reason why you prefer an interference fit and JB weld rather than key locking ?

 

[Foxy]

Gday Ludwig,
well Ive wonderd what you've been upto lately as theres beeen no posts from you for a number of weeks. Now we all know, thats one permanent heavy duty fix for them porous (poor as piss) exhaust threads! Just wondering, if the plate was stainless and brass nuts used, all polished, better bling look?? Other than that, looks good.
FOXY