Pictures of your Norton 961

I've replaced a few head gaskets on 961's...hence why the retorque procedure came about with Norton.
I'm not a metallurgist, but to me having two hitensile bolts in the centre and two stainless steel studs on each side, just didn't seem right. So I used high tensile throughout, torqued to 60nm.
 
In the modern automotive world it is common practice to fit ‘waisted stem’ bolts / studs in certain applications where it is important to both maintain high clamping force AND allow for flex to accommodate expansion and contraction due to heat cycles etc.

It’s also fairly common in the old Norton Commando world, sounds like the new Commandos need to catch up with the old skool tech…

coloradonortonworks.net

cNw Head Mounting Kit

Type 3 5 ea ARP/cNw 12 point head bolts. 3/8 – 26 thread. ARP 300 series, heat-treated stainless that is rated at 180KSI (180,000 psi) The 5 bolts above are also cut down in the center or ‘waisted’ in order to accurately maintain a torque 3 ea ARP head studs. 3/8 – 16 x 3/8 – 24. ARP 8740...
coloradonortonworks.net coloradonortonworks.net

jsmotorsport.com

High strength ARP stainless reduced shank studs and bolts for head and cylinders.

The fluted shanks allow the studs to stretch to prevent the threads from pulling out. The stretch keeps bolts and studs tight to help prevent oil leaks because they can stretch and contract along with…
jsmotorsport.com
 
Fast Eddie said:
In the modern automotive world it is common practice to fit ‘waisted stem’ bolts / studs in certain applications where it is important to both maintain high clamping force AND allow for flex to accommodate expansion and contraction due to heat cycles etc.

It’s also fairly common in the old Norton Commando world, sounds like the new Commandos need to catch up with the old skool tech…

coloradonortonworks.net

cNw Head Mounting Kit

Type 3 5 ea ARP/cNw 12 point head bolts. 3/8 – 26 thread. ARP 300 series, heat-treated stainless that is rated at 180KSI (180,000 psi) The 5 bolts above are also cut down in the center or ‘waisted’ in order to accurately maintain a torque 3 ea ARP head studs. 3/8 – 16 x 3/8 – 24. ARP 8740...
coloradonortonworks.net coloradonortonworks.net

jsmotorsport.com

High strength ARP stainless reduced shank studs and bolts for head and cylinders.

The fluted shanks allow the studs to stretch to prevent the threads from pulling out. The stretch keeps bolts and studs tight to help prevent oil leaks because they can stretch and contract along with…
jsmotorsport.com
Click to expand...
Are you meaning fasteners called “stretch to yield”. Use them once then pitch them? You torque them to a specific spec, then stretch the bolt / stud to a rotational degree to yield its clamping force.
 
Voodooo said:
Are you meaning fasteners called “stretch to yield”. Use them once then pitch them? You torque them to a specific spec, then stretch the bolt / stud to a rotational degree to yield its clamping force.
Click to expand...
No. Waisted stem fasteners are designed to work within their plasticity, ie they stretch and then contract again to retain their original length and integrity.

Hence the use on things like heads and barrels, they stretch with heat, and return to their original length, maintaining clamping force all the time.

If you use fasteners that are too inflexible in this application, then when the alloy expands, the heads of bolts can ‘dig in’ to the alloy head, and / or gaskets compress too much, then when it cools down, you have head bolts that are no longer clamping with the correct torque.

This is a fairly common problem on racing / hard used old Nortons and Triumphs.

I have no idea, but I wonder if those stainless studs on 961s were actually internationally specified with the coefficient of expansion in mind.
 
Fast Eddie said:
No. Waited stem fasteners are designed to work within their plasticity, ie they stretch and and then contract again to retain their original length.

Hence the use on things line heads and barrels, they stretch with heat, and return to their original length.

If you use fasteners that are too inflexible in this application, then when the alloy expands, the heads of bolts can ‘dig in’ to the alloy head, and / or gaskets compress too much, then when it cools down, you have head bolts that are no longer clamping with the correct torque.

This is a fairly common problem on racing and hard used old Nortons and Triumphs.

I have no idea, but I wonder if those stainless studs on 961s were actually internationally specified with the coefficient of expansion in mind.
Click to expand...
We call them torque to yield. It’s the same as you describe. A fastener is basically a spring. When tighten, it pulls the pieces together under tension.

The torque to yield bolts / studs can only be used one time. Once you use them on a cylinder head, Rod, main etc, and tighten them they are torqued to a very low torque value. Then you tighten it with a degree meter or wheel to a given specification.

Example:
On a cylinder head, you would tighten all the fasteners to say 30 nm in sequence. Then you would use a degree angle meter and tighten the fastener to the specific degree of angle. Say example of 90°.
Once that it reached, you’re done. You do not got any tighter.
But you can only use these fasteners one time.
If you ever loosen them, they are not to be reused again.
 
Voodooo said:
I just seen the link of the ARP studs you posted. That’s interesting, I never seen those in ARP before.
Click to expand...
When doing the head bolts on a big engine using degrees and not NM’s , five foot long power bar when the bolts start to stretch they feel like that they are going to break.
As they stretch the resistance seems to get less. Doing it for the first time goes against what you are used to with a torque wrench..
 
Stu Bodycote said:
Bit more done...got one intake trumpet built up. I'm going to have the sections welded, as I don't trust just a push fit. Loving the look of it now. Need my tank back from Dream Machine....then she's off on her jollies to Yorkshire, for a new exhaust system to be made.
Click to expand...
Hi Stu,
Is it safe to put headed titanium bolts instead of the threaded studs?
Thanks!
 
I would not use Ti bolts. The nuts have bottomed out on the stud threads and now the studs will unscrew when you unscrew the nuts. I have had good results using two (2) exhaust gaskets per exhaut port. This way you will have more crush before the nuts bottom out on the studs. Certainly replace any nuts that look bad or have corroded with quality stainless hardware .
 
TonyA said:
I would not use Ti bolts. The nuts have bottomed out on the stud threads and now the studs will unscrew when you unscrew the nuts. I have had good results using two (2) exhaust gaskets per exhaut port. This way you will have more crush before the nuts bottom out on the studs. Certainly replace any nuts that look bad or have corroded with quality stainless hardware .
Click to expand...
Also
If you use stainless nuts on stainless bolts or studs, don’t forget to use anti seize or else they’ll weld themselves together.
 
The standard studs are steel. The bolts in mine are stainless, with graphite paste. I cant see there being a problem using Titanium though, the likes of Probolt sell plenty grade 5 Ti exhaust kits for various bikes etc.
 
Whatever the material choice, I would not fit ‘bolts’ (as per the question). Studs stay put, making exhaust fitment easier and eliminating the risk of cross threads etc.
 

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