Head bolts cracks -stretch marks

Status
Not open for further replies.
I

Ian James

VIP MEMBER
Joined
Dec 16, 2019
Messages
169
Country flag
After reading posts about SS bolts cracking I loosened the head fasteners and removed the four long bolts these are SS that were supplied by RGM. On each one I could clearly see 6 or 7 fine lines running along the shank between the thread and the head most of them around 3/4 " long .These bolts have never held their tension for long and have been retightened frequently to 30fb , the threads were not lubricated. I was expecting to see radial cracks ,perhaps not? Any thoughts is what I was looking for? Cheers Ian
 
Ian
At 30ftlb I doubt the bolts are failing. Are you sure they're cracks and not some other kind of mark?
There is a wealth of information on this forum on "waisted" 3'8 head bolts - the theory being (which I subscribe to!) that the five 3/8" bolts are too strong (not enough stretch) so cause the aluminium head to creep at temperature giving the impression that the bolts are losing tension when the actually head is becoming very slightly thinner with each temperature cycle.
Waisting the bolts to 5/16" (eg ARP) or milling flats (JS) makes them stretchier without making them too weak to do the job.
Definitely worth thinking about
Cheers
 
Or if you have a FullAuto head made of or degrades to softer metal causing the bolts to pull the washers in to the metal.
 
The bolts are probably machined from 303 grade stainless which is a free cutting type, & not suitable in my opinion. The best bolts to use are the original type along with hardened thick steel washers. I'm sure that ARP bolts work just as well or better, but are also a lot more expensive.

Martyn.
 
robs ss said:
Ian
At 30ftlb I doubt the bolts are failing. Are you sure they're cracks and not some other kind of mark?
There is a wealth of information on this forum on "waisted" 3'8 head bolts - the theory being (which I subscribe to!) that the five 3/8" bolts are too strong (not enough stretch) so cause the aluminium head to creep at temperature giving the impression that the bolts are losing tension when the actually head is becoming very slightly thinner with each temperature cycle.
Waisting the bolts to 5/16" (eg ARP) or milling flats (JS) makes them stretchier without making them too weak to do the job.
Definitely worth thinking about
Cheers
Click to expand...
I had the CNW waisted bolts supplied when Jim did my head rebuild. I am profoundly impressed. I've checked 5 times, but NO MOVEMENT each time before the torque wrench clicks. These work as designed.
Thanks Jim!
 
I could dig around for the answer, but........ Is it a reasonable option to make waisted bolts from stock bolts, new or used? I should add that I have a lathe, mill, etc.
 
What Concourse and Robs SS said.
If you don't have confidence in the bolts you are using then switch them out for set from cNw/ARP.
Quality fasteners help eliminate a lot of grief .
 
TomU said:
True, these are good but not so easy to install. Maching is required.
Click to expand...

I restored my 74 Norton engine using ARP fasteners throughout.
No machining of any type was required.

ARP fasteners have been used on all my engine rebuilds over the years, automobile and motorcycle. I never had any need to modify one of their fasteners.
If in theory I did I would contact ARP. Their offerings are very extensive.

I know I sound like a sales rep but I am not.

You start screwing around with the structural integrity of a specifically designed fastener for a specifically designed application by removing material...more often than not things go bad in a hurry.
 
Stephen Hill said:
I could dig around for the answer, but........ Is it a reasonable option to make waisted bolts from stock bolts, new or used? I should add that I have a lathe, mill, etc.
Click to expand...
You can waist your own - I have for my 650SS.
Just be sure to polish out machining marks - ensures no stress raisers.
Cheers
 
TomU said:
True, these are good but not so easy to install. Maching is required.
Click to expand...
They are just a easy to install as the orginals.
If by "Maching" you mean Machining - there is no machining required if you use cNw/ARP.
 
Last edited:
robs ss said:
They are just a easy to install as the orginals.
If by "Maching" you mean Machining - there is no machining required if you but cNw/ARP.
Click to expand...
If by orginals you mean originals, this...

Note: There is one modification needed in order to use that above kit and that is to install ‘heli coils’ or ‘timeserts’ to change the thread for the head studs. Those studs are prone to pull out with the stock thread size and we require that a 3/8 – 16 thread gets installed in order to use the ARP head stud. This service is available from cNw of course if you don’t have a local shop that can do this modification
 
Hey guys,

For the full cNw / ARP head bolt kit you do have to install a thread insert for the 3 head studs as that thread is changed to a 3/8-16 (UNC). This may be what was considering ‘machining’ but it’s more of a modification and very important as the stock fine thread is weak and notorious for getting compromised over the years causing the studs to pull out (while I was typing…slowly….TomU confirmed already)

ARP does not offer any BSW hardware. These waisted, formed, head bolts are made for me. I had to buy the thread forming tool for the 3/8-26 so they could make them

Also worth mentioning. Big difference between a formed waisted bolt and a machined one. With a formed bolt and rolled thread you retain the molecular integrity of the material (ultimately strength) as none of it is lost, it’s essentially just moved around as it’s being shaped.

When machining a bolt you remove material and and break down the structure of the bolt. Threads are also much weaker when cut into straight stock versus rolling

Someone is offering a machined (modified) ARP head bolt but this cutting process goes against ARPs recommendation and those bolts will not spec out like their formed hardware. The threads on this modified bolt are also cut, not rolled, like they would be if ARP made them. Be aware that you are not using ARP manufactured hardware if installing these.

ARP hardware is as nice as it gets and maybe overkill in some applications but I think our Commandos deserve it

Matt
 
Last edited:
I have to agree with you Matt, ARP fastners are superb. I've just fitted a set of their big end bolts/nuts to my A65 build to give me peace of mind, as I have no idea who makes the normally available ones, let alone what they are made from. It's just a shame that ARP stuff is so expensive in the UK.

Martyn.
 
Matchless said:
I have to agree with you Matt, ARP fastners are superb. I've just fitted a set of their big end bolts/nuts to my A65 build to give me peace of mind, as I have no idea who makes the normally available ones, let alone what they are made from. It's just a shame that ARP stuff is so expensive in the UK.

Martyn.
Click to expand...
What's a shame is, modern marketing of (all kinds of things) fasteners is so shamefully suspect, maker doesn't even put the name on the package/product.
So we are forced to choose:
1) take a chance on possibly cheese material, shoddy machining from goodness knows where/what/who
2) GREAT quality, 12,000hp Top Fuel Dragster championship winning quality level to use in our humdrum street bikes. At the race car price.
 
So when you guys retorque your heads do you just set your T wrench to the setting and see if it will click, or give some more torque ? , my experience with retorque-ing is to mark your fastener or know its position and just crack it off then follow through with the torque setting , in a smooth movement, because break away torque will always exceed the setting .cheers
 
Shelby-Right said:
So when you guys retorque your heads do you just set your T wrench to the setting and see if it will click, or give some more torque ? , my experience with retorque-ing is to mark your fastener or know its position and just crack it off then follow through with the torque setting , in a smooth movement, because break away torque will always exceed the setting .cheers
Click to expand...
" rolling torque" not specified.
 
Status
Not open for further replies.
Back
Top