Stainless head fastener torque settings

oldschool · 2026-09-23T02:17:50-0600

The cylinder head bolts, studs, nuts etc on my Mk3 are all pretty tired and I was considering replacing them with stainless steel items. I'm not looking at waisted bolts, just standard format.
I've read that expansion rates of common stainless steel fixings are greater than ht steel, so should torque settings for stainless fixings be any different from the original steel ones?

MexicoMike · 2026-09-23T03:11:26-0600

One thing to consider when replacing fittings - are they the same grade? If they are not, then the OEM torque settings are probably no longer correct. If, for example, the OEM fittings are grade 2 and you replace them with grade 5, the torque settings have to be considerably higher for the fittings to properly stretch. BUT you can distort components with excessive torque on the fittings.

One case where the OEM torque specs would not change regardless of the bolt grade is if a bolt is scewed into an aluminum component because the torque setting, in that case is based on the weakness of the AL.

oldschool · 2026-09-23T05:00:53-0600

MexicoMike said:
One thing to consider when replacing fittings - are they the same grade? If they are not, then the OEM torque settings are probably no longer correct. If, for example, the OEM fittings are grade 2 and you replace them with grade 5, the torque settings have to be considerably higher for the fittings to properly stretch. BUT you can distort components with excessive torque on the fittings.

One case where the OEM torque specs would not change regardless of the bolt grade is if a bolt is scewed into an aluminum component because the torque setting, in that case is based on the weakness of the AL.

Thanks Mike. The difficulty I find is that the various sellers of stainless bolts etc for Nortons do not divulge which grade they use, so it's guesswork!

Here's an example: https://www.feked.com/norton-commando-750cc-850cc-cylinder-head-bolt-kit-stainless.htmlsrsltid=AU7gw4VfzmeKsUzTWxr3i4fUccjuFTlncN7lycI0UZWTwH7cvhtQTAbS

I've emailed Feked to see if they have the information.

robs ss · 2026-09-23T05:03:34-0600

oldschool said:
The cylinder head bolts, studs, nuts etc on my Mk3 are all pretty tired and I was considering replacing them with stainless steel items. I'm not looking at waisted bolts, just standard format.
I've read that expansion rates of common stainless steel fixings are greater than ht steel, so should torque settings for stainless fixings be any different from the original steel ones?

No. Just means the crushing effect due to differing expansion rates is reduced. Good thing. Go waisted.
ARP are a good grade (and waisted).
Cheers

kommando · 2026-09-23T05:22:13-0600

You have to assume these are made with cheap stainless steel unless told otherwise, so they will be softer than mild steel let alone hi-tensile steels. A regular wipe with an oily rag will keep the plated steel rust free if that is what you are after.

oldschool · 2026-09-23T05:47:46-0600

kommando said:
You have to assume these are made with cheap stainless steel unless told otherwise, so they will be softer than mild steel let alone hi-tensile steels. A regular wipe with an oily rag will keep the plated steel rust free if that is what you are after.

You're probably right! Also, I've bought stainless nuts and bolts before, advertised as 'bar-turned' and the threads were very loose.

Tigernut · 2026-09-23T05:47:55-0600

Stainless head bolts are almost always made from A2 stainless steel, which is of lower tensile strength than original head bolts. In practice, I'm not convinced it matters much because the torque settings are quite low and even a 3/8" stainless bolt of lower tensile strength than an original isn't going to be remotely over-stressed. I get the theory but I've had a set of stainless head bolts on my T140 for years (just because I like the look) without problems. I used the standard torque figures.

Skoti · 2026-09-23T06:00:48-0600

My head gasket used to weep a bit oil with stainless bolts fitted, on Mick Hemmings advice I refitted the original bolts and that cured the weep.

Hemmings told me he wouldn't fit stainless steel fasteners because you don't get the 'same feel' when you nip them up.

Schwany · 2026-09-23T07:56:20-0600

Not an issue.

Only negative thing I can come up with regarding stainless fasteners for a Norton engine is they are over priced from the popular suppliers. Just saying

jimbo · 2026-09-23T08:56:35-0600

One thing I found to help to maintain clamping force is to use thick high grade washers

lcrken · 2026-09-23T11:33:50-0600

The stainless fasteners from ARP that I use for head and cylinder bolts is made of their ARP "Stainless 300" alloy, with a tensile strength of 170,000 psi. For comparison, a Grade 8 steel fastener typically has a tensile strength of 150,000 psi. Seems good enough to me.

Ken

lcrken · 2026-09-23T11:53:09-0600

FWIW, the stainless head bolts kits available for Commandos are custom made for them by ARP from the "Stainless 300" alloy, and are rated by CNW at 180,000 psi. ARP lists them on it's material spec page at 170,000 psi to 190,000 psi. Either way, certainly sufficiently strong.

Ken

Stainless head fastener torque settings

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