Stainless nuts 'n bolts

[HCA]

Are there any metallurgists amongst us?

I have always wanted to put to bed the arguments against stainless bolts - when they should be used and not used.

I just treated myself to a pack of stainless engine fixtures on the basis that I am going to need new bolts anyway, so a few quid extra for stainless is not much (I hasten to add that for the internals, I am using ARPs... ) They arrived yesterday and all nicely packaged and labelled.

OK, the likes of sump and front cover bolts will be fine, but what about the likes of engine to bell housing and engine mounts? Will stainless be ok here? At what point do/might stainless bolts sheer?

[promotor]

Unless they are high grade, stainless bolts aren't as strong as the original bolts found on the engine.

As for stainless into aluminium, it's not a good idea as they have a reaction between the materials. I know this is an engine discussion but I never fit stainless bolts to hold the diff unit into the aluminium final drive casing. Some people would recommend anti-seize paste or copper grease etc, but the better way around it is to not fit stainless bolts at all!

BZP (bright zinc plated) bolts are better but even they start to oxidize, and some I've seen aren't that well made.

It may be contentious but I prefer original good quality bolts (as long as they haven't been stretched or damaged) even if they will go rusty, over modern replacements.

[2cams70]

+1 Anyone throwing out original GKN, GSF, Wiley or LBS bolts please send them my way!! Quality British stuff.

For the most common grade S bolts I get them re-plated and they come up like new. Blue zinc, gold zinc, black zinc depending on what was original. Black zinc is a good substitute and longer lasting where bolts were originally black oxide coated. For high grade highly stressed bolts I prefer to just clean due to the risk of hydrogen embrittlement from the plating process.

The problem with bolts these days and particularly the stainless steel variety is that they are produced in the millions in China and you can never be sure of the origin, the quality and whether the specification is as claimed.

[Mazzini]

Unless they are high grade, stainless bolts aren't as strong as the original bolts found on the engine.

As for stainless into aluminium, it's not a good idea as they have a reaction between the materials. I know this is an engine discussion but I never fit stainless bolts to hold the diff unit into the aluminium final drive casing. Some people would recommend anti-seize paste or copper grease etc, but the better way around it is to not fit stainless bolts at all!

BZP (bright zinc plated) bolts are better but even they start to oxidize, and some I've seen aren't that well made.

It may be contentious but I prefer original good quality bolts (as long as they haven't been stretched or damaged) even if they will go rusty, over modern replacements.

I use a special anti-seize paste, but on reflection I think Al is right. I save and replate the original bolts.

[bitsobrits]

I am using ARPs... ) They arrived yesterday and all nicely packaged and labelled.

OK, the likes of sump and front cover bolts will be fine, but what about the likes of engine to bell housing and engine mounts? Will stainless be ok here? At what point do/might stainless bolts sheer?

If you are using genuine ARP stainless, these are a high tensile strength fastener suitable for most any application you can throw at them, including block to bell housing, suspension, body and engine mounts, etc. I've use them extensively in various builds for many years in my Lotii and other brands. I would only recommend suitably graded stainless fasteners for any critical/safety application. BTW-ARP is probably the global leader in con-rod fasteners, so they know a thing or two about making high strength fasteners. Check out ARP-bolts.com (no affiliation)

In any critical application, I would never mount threads in shear (regardless of fastener metal) and always use a bit of nickel based anti-seize on the threads of stainless fasteners, regardless of grade.

While I understand the theoretical aspect of avoiding dissimilar metals in contact with each other, in hobby car automotive use in decades of rebuilding old cars I've never once seen or experienced any issue with this. I use stainless fasteners in alloy all the time. My longest owned car (since 1988) has come apart and gone back together just fine over the years with stainless bolts and studs threaded into alloy. I do prefer studs in some cases, like the diff unit to housing interface, just to reduce wear on the alloy threads.

[HCA]

Unless they are high grade, stainless bolts aren't as strong as the original bolts found on the engine.

This is exactly as I have been brought up to think, but, what is strong and where is strong needed on an engine? Obviously not for covers, but for the bell housing?

As for stainless into aluminium, it's not a good idea as they have a reaction between the materials.

This I did not know, so will add it to my long list of 'not how to do things'!

If you are using genuine ARP stainless, .

To be clear, I do not know if they are ARP stainless as such - they are the compound supplied through QED for cylinder head, conrods and flywheel...the stainless fasteners I ask about are for the externals of the engine.

[StressCraxx]

It's acceptable to use stainless fasteners on the engine exterior if one uses the right grade. Marine hardware supply companies carry them.

This is fastener supply company from India, but ASTM fastener specs are worldwide.
https://www.jigneshsteel.com/astm-a320- ... studs.html

[snowyelan]

The site below will give you a basic way of comparing the SS you have to what you want to replace in terms of tensile strength using the head markings. If they are not marked....

I personally only use SS in applications that are not tapped and not function critical.

https://www.engineersedge.com/hex_bolt_ ... cation.htm

[Andy8421]

Unless they are high grade, stainless bolts aren't as strong as the original bolts found on the engine.

As for stainless into aluminium, it's not a good idea as they have a reaction between the materials. I know this is an engine discussion but I never fit stainless bolts to hold the diff unit into the aluminium final drive casing. Some people would recommend anti-seize paste or copper grease etc, but the better way around it is to not fit stainless bolts at all!

While I understand your point about corrosion, it is common in the marine world to use stainless bolts with aluminium parts, even in areas washed by salt water.

[ericbushby]

Hi Andy
I am pleased you mention that. Back in the 1970`s when I was playing about with Evinrude outboard motors we assembled the aluminium castings using stainless steel screws liberally coated with lanolin.
I have often wondered since why that was OK.
Eric in Burnley
1967 S3SE DHC

[promotor]

Unless they are high grade, stainless bolts aren't as strong as the original bolts found on the engine.

As for stainless into aluminium, it's not a good idea as they have a reaction between the materials. I know this is an engine discussion but I never fit stainless bolts to hold the diff unit into the aluminium final drive casing. Some people would recommend anti-seize paste or copper grease etc, but the better way around it is to not fit stainless bolts at all!

While I understand your point about corrosion, it is common in the marine world to use stainless bolts with aluminium parts, even in areas washed by salt water.

Agreed, I still won't do it though. I know that if a steel bolt is in an aluminium thread it'll more than likely still come out in 40 years time without issue. Stainless steel into aluminium it would be on my mind that it wouldn't.

From a stand point of rebuilding diffs for customers I wouldn't put them in as I know aluminium casings with steel bolts work well. I've not seen stainless steel bolts that have been in application for even 5-10 years to compare so I have to go with what I know works for a long period of time and without being checked over regularly, perhaps unlike the marine industry.

I'm not informed enough to make a definite call on aluminium and stainless steel but I do know it's a metallurgical problem, and that steel bolts into aluminium works well from a point of view of being able to remove them without issue, particularly in an environment where bolts aren't regularly checked, like a diff unit in a place that's hard to get to, like an Elan!

I very rarely read about normal steel bolts being a problem to remove from aluminium, but it seems to crop up regularly when using stainless steel.

I'm cautious though and that's boring, I know!