Improved head bolts

A recent conversation elsewhere about head fasteners prompted me to share this:

I’m currently running two Commando motors, a 920 and a 1007.

Both of these have bigger bores than stock and alloy barrels.

Both of those facts above present extra challenges when it comes to head gasket sealing.

Both motors are (currently, touch wood) sealing perfectly in terms of combustion and oil. The 920 in particular has been together several years now and has been used on the track and the road.

Both motors use copper gaskets (no other choice with these configurations).

I attribute at least part of this success to the use of high quality, waisted shank fasteners.

I know these aren’t for everyone, but I believe they help with gasket sealing in a big way as they allow stretch, whilst maintaining clamping force, whilst preventing bolts over stretching or gaskets or aluminium faces being crushed.

We are lucky to have two suppliers who’ve done all the hard work and supply these for us. I’ve used parts from both, both highly recommended IMO (the small 12 point heads also make access and tightening MUCH easier):

I've had the Comstock waisted bolts on for 6 years.
Great results.

Fast Eddie said:

A recent conversation elsewhere about head fasteners prompted me to share this:

I’m currently running two Commando motors, a 920 and a 1007.

Both of these have bigger bores than stock and alloy barrels.

Both of those facts above present extra challenges when it comes to head gasket sealing.

Both motors are (currently, touch wood) sealing perfectly in terms of combustion and oil. The 920 in particular has been together several years now and has been used on the track and the road.

Both motors use copper gaskets (no other choice with these configurations).

I attribute at least part of this success to the use of high quality, waisted shank fasteners.

I know these aren’t for everyone, but I believe they help with gasket sealing in a big way as they allow stretch, whilst maintaining clamping force, whilst preventing bolts over stretching or gaskets or aluminium faces being crushed.

We are lucky to have two suppliers who’ve done all the hard work and supply these for us. I’ve used parts from both, both highly recommended IMO (the small 12 point heads also make access and tightening MUCH easier):

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

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...

Do you need to re-torque those?

cliffa said:

Do you need to re-torque those?

Click to expand...

No comment !!

The below commentary is not intended for FF. It is just information somebody somewhere on earth with an old Norton might get something out of.

I have a mix of cNw and JSM wasted shank bolts, and 4 solid shank bolts near the spark plugs going into alloy barrels on a little 750 engine. The no need to retorque mentioned in the instructions is overly optimistic marketing speak. However, if Pliobond is used on the head, the head gasket might not leak even if the bolts did need to be retorqued on a 750. Things are probably different with the larger displacement engines. They may always need to be retorqued. Don't know though myself.

Important note for those that are considering the cNw or JSM wasted shank bolts is read the instructions. Helicoils, Time-serts, or similar are needed in the head stud locations and possibly in older cases for the barrel through bolts. Point is you can't just buy them and use them without some machine work if the machine work hasn't already been done. Also the cNw head bolts next to the plugs don't work in Molnar alloy barrels. That may also apply to the JSM bolts. The threads are unique in those 4 locations in the Molnar barrels. I used Molnar head bolts in those 4 locations.

Am I shocked that Andy has done something different Schwaney lol.
No I'm not!
My mate runs a AJS 7R
it's all Molnar now! lol.

Chris said:

Am I shocked that Andy has done something different Schwaney lol.
No I'm not!
My mate runs a AJS 7R
it's all Molnar now! lol.

Click to expand...

Steve’s are different as well. But JS caters for these. @ Jim Schmidt, maybe it’s worth catering for Andy's barrels too ?

Fast Eddie said:

A recent conversation elsewhere about head fasteners prompted me to share this:

I’m currently running two Commando motors, a 920 and a 1007.

Both of these have bigger bores than stock and alloy barrels.

Both of those facts above present extra challenges when it comes to head gasket sealing.

Both motors are (currently, touch wood) sealing perfectly in terms of combustion and oil. The 920 in particular has been together several years now and has been used on the track and the road.

Both motors use copper gaskets (no other choice with these configurations).

I attribute at least part of this success to the use of high quality, waisted shank fasteners.

I know these aren’t for everyone, but I believe they help with gasket sealing in a big way as they allow stretch, whilst maintaining clamping force, whilst preventing bolts over stretching or gaskets or aluminium faces being crushed.

We are lucky to have two suppliers who’ve done all the hard work and supply these for us. I’ve used parts from both, both highly recommended IMO (the small 12 point heads also make access and tightening MUCH easier):

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

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...

The 12 point bolts work great especially for re-torque with an electric starter
Mike

Ok I'm quite prepared to be knocked down and sit in the corner
But is there a reason you can't machine a set of standard head bolts to do this?

baz said:

But is there a reason you can't machine a set of standard head bolts to do this?

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No, as long as you start with the right head bolts, which is not a standard one, the required spec is in the CNW link. But when you factor in the setup time etc best just to buy the finished product from either source. If you were to use standard bolts then you would need to know the spec and material properties and then calculate the required waisting dimensions to get the same effect.

Fast Eddie said:

Steve’s are different as well. But JS caters for these. @ Jim Schmidt, maybe it’s worth catering for Andy's barrels too ?

Click to expand...

I already supply reduced shank through cylinder bolts with the 12 point heads For Molnar cylinders but you would have to grind down the OD of the socket to .530" OD to get it to fit the smaller bolt head recess - either that or provide allen bolts and reduce the diameter of the allen head. But Andy's head to cylinder bolts near the spark plugs require 20 threads per inch. From what I understand he uses BSA A 10 head bolts. I could set that up but its an odd thread. I would prefer to find an existing 20 tpi allen bolt and reduce the shanks but allen bolts of the correct length in 20 tpi are hard to find.

baz said:

Ok I'm quite prepared to be knocked down and sit in the corner
But is there a reason you can't machine a set of standard head bolts to do this?

Click to expand...

All my comments on this site are typed while sitting in the corner wearing a dunce cap. Saves me time not having to move back and forth and keeps my head warm.

If you did this stuff in a small shop using standard head bolts, my guess is they would stretch funny or break. When I torqued down the long skinny JSM barrel through bolts I thought they would snap, but they are processed to take the torque applied with the reduced shank.

jseng1 said:

I already supply reduced shank through cylinder bolts with the 12 point heads For Molnar cylinders but you would have to grind down the OD of the socket to .530" OD to get it to fit the smaller bolt head recess - either that or provide allen bolts and reduce the diameter of the allen head. But Andy's head to cylinder bolts near the spark plugs require 20 threads per inch. From what I understand he uses BSA A 10 head bolts. I could set that up but its an odd thread. I would prefer to find an existing 20 tpi allen bolt and reduce the shanks but allen bolts of the correct length in 20 tpi are hard to find.

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Your 12-point reduced shank through bolts worked as delivered on my Molnar barrels. I used a thin wall 1/4" drive socket to fit in the through bolt recess. No grinding was required. I got lucky though because I have a good selection of 1/4" drive sockets, but only one that fit in there.

Regular black 20 tpi high tensle hex bolts may be available for the Molnar head to cylinder bolts. Then the shanks would need to be reduced so they can stretch. But would anyone pay extra for regular looking head bolts?

jseng1 said:

Regular black 20 tpi high tensle hex bolts may be available for the Molnar head to cylinder bolts. Then the shanks would need to be reduced so they can stretch. But would anyone pay extra for regular looking head bolts?

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Molnar's head bolts kits are stainless with regular 5-point heads. Heck of a lot cheaper than 12-point. No black bolt option.

His barrel through bolts are black Allen head and kind of wonky IMO. They look the same as what AN sells.

jseng1 said:

Regular black 20 tpi high tensle hex bolts may be available for the Molnar head to cylinder bolts. Then the shanks would need to be reduced so they can stretch. But would anyone pay extra for regular looking head bolts?

Click to expand...

Different pitch = different torque.
What value would you suggest for 20 TPI ?

jseng1 said:

From what I understand he uses BSA A 10 head bolts.

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No, he doesn't. His bolts are machined in his shop (meaning threads are turned, not rolled, as would be preferred).
Andy conveyed this to me.

- Knut

mdt-son said:

No, he doesn't. His bolts are machined in his shop (meaning threads are turned, not rolled, as would be preferred).

- Knut

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Perhaps you’re both right, ie they are stainless bolts for A10s that he makes (stainless fasteners for Brit bikes was his main business for years).

I definitely agree re rolled threads, which is one reason for me liking ARP stuff.

I have been using ARP's offerings for a lot of years on racing and street engines. When researching what I believed to be the best way to rebuild my 850 engine cNw's ARP fastener kit was exactly what I wanted. Plus a really top notch Norton guru had already done the legwork to compile the right ARP fasteners for my specific applications. I chose Matts fastener kit to rebuild my 850 engine and a variety of his other fastener kits to complete my overhaul.
One of the best decisions I could have made for my Norton restoration, never looked back.

ludwig said:

Different pitch = different torque.
What value would you suggest for 20 TPI ?

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I used 30 ft lb on the Molnar head bolts, but I definitely had to retorque them with a composite gasket. Oops, just noticed you are asking Jim. Forgive the intrusion.