Wo is me!

I found those AN studs a bit short as well, although the originals on hand here were about the same.

www.accessnorton.com

Head studs

I needed to make some special head studs to fit the alloy 920 barrel. The barrels require a longer stud but the stud must be reduced from 3/8 to 5/16" and fitted with the small diameter type 5/16" nuts. The length is needed because the cylinder is different than the stock item. The reduction in...
www.accessnorton.com www.accessnorton.com
 
Maybe they were actually ok 50 years ago and are now a more pronounced issue due to the heads softening with heat over the decades ?
 
Fast Eddie said:
Maybe they were actually ok 50 years ago and are now a more pronounced issue due to the heads softening with heat over the decades ?
Click to expand...
Could be but best I can tell, the factory was not using their drawing's thread lengths. Apparently, they knew that longer was needed.
 
So back in my days of general mechnic-ing at the co-op hippie-dippie garage on Seattle's Jackson street, there was a rash of VW 411 cases whose aluminum was so weak that the studs would not hold the head tight enough not to leak. We could hear them coming up the block and bet whether they'd turn into the shop. The ultimate fix was new cases but I and others tried the heilicoil cure and later the oversize insert cure. Anything but new cases only postponed the problem long enough for the owner to sell the car.

I have encountered some very dubious Norton Commando head castings. One that came on a bike I bought was pourous in the exhaust spring seat and leaked oil into the exhaust port following a thread renewal by the previous owner. Several others pulled the studs Greg is dealing with. In those days there was a basement full of junk bikes to pull parts from. We also did BMWs and never encountered bad castings. I don't know how to test the quality of old aluminum castings but if someone has a method it could save everybody a bunch of trouble. Is there some sort of Rockwell-like hardness test that could be used? Then we wouldn't have to muck about with doomed heads or cases, etc.
 
Thomasa said:
I have encountered some very dubious Norton Commando head castings.
Click to expand...
I recall hearing (probably in this forum) about someone selling a bunch of Commando heads with various flaws, imperfections, and incorrect machine work. I believe I recall the matter being explained as the batch having been factory rejects that the seller somehow acquired, and don't recall the details regarding how they were being presented/described at the point of sale...

Would the vernacular be "how they were being flogged (off)"?
 
Nothing more annoying than pulling a stud from a freshly rebuilt engine.
No matter how good they look, I always helicoil ( or insert) the 3 stud holes.
The std studs are too short: not enough thread on both ends.
You can make longer studs from head bolts.

Wo is me!

Helicoils are ok, but with inserts, you have the choice of threads.
I use M14 x 2 mm.

Wo is me!

Comstock is THE man, but I hear from turnaround times of several months.
It takes me a few hours for the 3 studs + inserts.
It's not that hard to do..
 
Last edited:
Thomasa said:
So back in my days of general mechnic-ing at the co-op hippie-dippie garage on Seattle's Jackson street, there was a rash of VW 411 cases whose aluminum was so weak that the studs would not hold the head tight enough not to leak. We could hear them coming up the block and bet whether they'd turn into the shop. The ultimate fix was new cases but I and others tried the heilicoil cure and later the oversize insert cure. Anything but new cases only postponed the problem long enough for the owner to sell the car.

I have encountered some very dubious Norton Commando head castings. One that came on a bike I bought was pourous in the exhaust spring seat and leaked oil into the exhaust port following a thread renewal by the previous owner. Several others pulled the studs Greg is dealing with. In those days there was a basement full of junk bikes to pull parts from. We also did BMWs and never encountered bad castings. I don't know how to test the quality of old aluminum castings but if someone has a method it could save everybody a bunch of trouble. Is there some sort of Rockwell-like hardness test that could be used? Then we wouldn't have to muck about with doomed heads or cases, etc.
Click to expand...
Back in my mechanic days we had a Norton customer with a persistent oil leak at the banjo fitting on the right side of the head. We replaced the crush washers but nothing worked. Then we cleaned the area, sprayed it with white foot powder and looked for tell tail tracks. Sure enough the head had a crack just below the banjo. I think quality control was something that went way beyond assembly in the British motorcycle industry.

I remember when every little town it seems had it's own bad tempered master machinist with a little dark shop. Those guys are all gone now.
 
Received the RGM studs today. In the picture, top is AN, bottom is RGM. As best I could I laid them side-by-side where the tighten in they head. The RGM has significantly more threads on the head end. Still need to do some pull-out testing, but it's pretty clear to me that the RGM studs are much less likely to pull out! On top of that, I pay trade prices to both companies - delivered they are $1.40 less each from RGM.


Wo is me!
 
I've made them out of 304 ss on the lathe, it only takes a few minutes. Tested to destruction the ss studs broke at 65 ft lbs, plenty of strength in reserve.
For fun I tested a spare CNW ss barrel stud of the same size and it also broke at 65 ft lbs.

Wo is me!
 
An interesting thing that I haven't studied/documented enough yet to draw conclusions:

The BSF threads on original studs and AN studs are visibly poorer quality (to my eye) than the threads on the RGM studs. And the RGM studs are a snug fit all the way in and can get pretty tight when they get to the unused threads deep in the hole. So, I tried running a brand-new Token bottoming tap in one hole in the combat head. That made the original and AN studs even more sloppy. The RGM stud then went all the way in with fingers but was not sloppy at any point after three turns.

I have no idea if the original, AN, or RGM threads are rolled, turned, or cut with a die. In any case, the tooling is much better on the RGM studs.
 
franko said:
Would it be possible to have a jig similar to this made up and do your own repairs? Maybe have a deeper depth to keep the drill straighter.
www.advrider.com

Airhead Cylinder Stud Thread Repair Jig

Here are a few poor pics of a jig Cycle Works is offering for repair of stripped cylinder stud threads on 1970-1995 airheads. This tool is designed for...
www.advrider.com www.advrider.com
Click to expand...
Actually thinking about making something similar. I was given a 2" thick piece of aluminum. It occurred to me that I can get a long 3/8" drill bit, put a set of cylinders upside down on it and drill the outer holes for registration. Then with some careful measuring locate the stud holes and drill oversize to fit the bit for the inserts. It's big enough that I could have different guides in one block of aluminum. Probably would need to sleeve the holes in some way to prevent them from wallowing out.

Or I can checkout the mill that's in my cart - just trying to be sure the quill can go high enough to clear the bottom of the head when locked down at its base.
 
marshg246 said:
I promised to do some testing and I've done quite a bit. I'll probably do a destructive test when I find an appropriate head - the head I thought I had I can't find.

Still, this is telling: https://www.gregmarsh.com/MC/Norton/HeadStudStudy.aspx

If you don't understand something or see typos (my specialty), I would like feedback (marshg@gregmarsh.com)
Click to expand...
If you already read this and found it interesting, read it again. I added a lot today, the quick update is that the RGM studs are a decent answer to stop the studs from pulling but they are not plug and play and they have some quality issues after all.

On the mill front, the $4000 mill I was looking at appears to not have enough quill height to work on a Norton head. It might just be possible with collets rather than a chuck but even that's iffy since you have to do something lock the head in position - studying that now.
 
marshg246 said:
If you already read this and found it interesting, read it again. I added a lot today, the quick update is that the RGM studs are a decent answer to stop the studs from pulling but they are not plug and play and they have some quality issues after all.

On the mill front, the $4000 mill I was looking at appears to not have enough quill height to work on a Norton head. It might just be possible with collets rather than a chuck but even that's iffy since you have to do something lock the head in position - studying that now.
Click to expand...
Well done Greg. Thanks!!
 
marshg246 said:
If you already read this and found it interesting, read it again. I added a lot today, the quick update is that the RGM studs are a decent answer to stop the studs from pulling but they are not plug and play and they have some quality issues after all.

On the mill front, the $4000 mill I was looking at appears to not have enough quill height to work on a Norton head. It might just be possible with collets rather than a chuck but even that's iffy since you have to do something lock the head in position - studying that now.
Click to expand...
I just updated the study again - very surprising results! I decided not to do the destructive test. I'm building three engines right now and will use new studs in all - if any pull (extremely doubtful) I'll have that answer and if none do, I'll just keep moving.
 

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