Manifold Fixings

[Nigel Triumph]

I'm probably not alone in finding it's quite a time consuming fiddle to fit the clamps, washers and nuts that hold the manifolds to the cylinder head on 6 pot engines. 

I wonder if 3/8 unf allen bolts of appropriate length would be easier, using a nice slim socket set to tighten.  Better still if they were stainless.  Can any of the wise and learned ones here see a drawback? 

Nigel

[RogerH]

Hi Nigel,

 do not rely on a stainless bolt not to seize in the steel head. The stainless properties can break down when in contact with a rust source.

I would stick with the copper coated steel studs and brass nuts.

 

Roger 

[Waldi]

Hi Nigel,

most common (austenitic) stainless steel bolts have a yield stress (the point where the metal gets permanent elongation) at about 1/3rd of most common “steel” bolts, so they are much weaker.

”Steel” bolts are alloyed with Chrome, Molybdenum and Vanadium to give the high strength (much higher than say steel construction beems).

Steel Allen screws would work I think, but like Roger, I prefer the original design. If a steel allen screw gets hot and corroded from rain etc, it will easily go round when you need to undo it after a couple of years.

That said, several modern cars use torx or equivalent designs for this application.

Waldi

 

 

[Nigel Triumph]

Thank you for your input gents. I understand the point about stainless being weaker.

I also have a Scimitar, fitted with a Ford Essex V6. These are well know for exhaust manifold studs snapping due to the nuts rusting on and studs rusting into the heads. Allen bolts seem to be the preferred option over there, but on the TR6, I'm thinking more about ease of access than corrosion trouble.

I will probably try steel Allen bolts as it's unlikely torx are available with unf thread.

Nigel

[RogerH]

Hi Nigel,

if you go for the steel Allen bolts then coat with copperslip etc. It may help them not to seize.

 

Roger

[Mike C]

+1  copper or graphite based  grease.

[Waldi]

Another reason to avoid austenitic SS bolts in this warm application is the risk for “breaking due to salts”.

This is known as Chloride Stress Corrosion Cracking in industry.

Background for those interested: When SS stressed materials (and some other materials) are exposed to chlorides (as in salt) at temperatures above approx. 60C in a humid environment, they can spontaneously break from trans-granular cracking. The stress can be from a load, like in a bolt, or residual stress from welding or bending etc.

Waldi

[BlueTR3A-5EKT]

26 minutes ago, Waldi said:

Another reason to avoid austenitic SS bolts in this warm application is the risk for “breaking due to salts”.

This is known as Chloride Stress Corrosion Cracking in industry.

Background for those interested: When SS stressed materials (and some other materials) are exposed to chlorides (as in salt) at temperatures above approx. 60C in a humid environment, they can spontaneously break from trans-granular cracking. The stress can be from a load, like in a bolt, or residual stress from welding or bending etc.

Waldi

Thank you Waldi for that info on stainless fasteners.

the MGBGT V8 suffers from very inaccessible ex manifold attacmhments so the parts world offers these in zinc plated steel.  https://mgbhive.co.uk/product/v8-2/mgb-gt-v8-allan-key-manifold-to-head-bolts-set-of-16/

 

cheers. 

Peter W

Edited May 9, 2019 by BlueTR3A-5EKT

[Nigel Triumph]

Thank you for all the knowledge imparted.

I like the MG idea. Zinc plated Allen bolts with copper grease sounds the best option. I will let you know how well it works... in about 5 years.

Nigel

[astontr6]

2 hours ago, Waldi said:

Another reason to avoid austenitic SS bolts in this warm application is the risk for “breaking due to salts”.

This is known as Chloride Stress Corrosion Cracking in industry.

Background for those interested: When SS stressed materials (and some other materials) are exposed to chlorides (as in salt) at temperatures above approx. 60C in a humid environment, they can spontaneously break from trans-granular cracking. The stress can be from a load, like in a bolt, or residual stress from welding or bending etc.

Waldi

Hi Waldi!

I have used 304 S/S Salt water grade nuts and bolts in non stress areas on my TR for years and never had any trouble with shearing or rusting. My view is that they are very good for exhaust pipe mountings. I do not know about the manifold as I have always used brass nuts. My system came apart very easily after 20 years of use. If you want high tensile S/S you would have to use Aerospace Aero engine grade and then you are looking at a very high expense, as used by RR on their aero engines.

Bruce.

[RogerH]

14 minutes ago, astontr6 said:

Hi Waldi!

 If you want high tensile S/S you would have to use Aerospace Aero engine grade and then you are looking at a very high expense, as used by RR on their aero engines.

Bruce.

Hi Bruce,

            generally speaking Stainless Steel as we know it (nice shiny stuff that doesn't rust) isn't used for serious situations on the aircraft.

What they do have is Corrosion Resistant steel (CR). These are usually grey or brown (ish) in appearance. Rather like the tubular exhaust manifolds on our cars.

And yes - bl**dy expensive.

Interestingly, the stainless steel work tops in the galleys are in fact anodized Aluminium alloy. Very hard wearing but light weight.

 

Roger

[Waldi]

For our cars, there should not be much of an issue using galvalized bolts, even on a manifold.

Waldi

Edited May 10, 2019 by Waldi
Removed confusing information.

[Nigel Triumph]

Hi Waldi, 

Please don't apologise, this is fascinating. I studied chemistry many years ago and some of this makes sense!

Nigel

[Tom Fremont]

The manifold tightening torque specified in Uncle Bentley correlates to the lowest grade of bolt, half that of a high grade one. So the tensile stress is low, and if a stainless bolt is rated for 25 lb-ft I see no reason not to use it...other than the matter of wearing out the threads in the cast iron head a little. This is mitigated when a lubricant is used ( here in the 'States we like Never Seize which uses nickel powder ). I'm not convinced installation will be easier with bolts, however.

I've been quite happy with the standard studs and stainless nuts/lockwashers, copiously lubricated with Never Seize. The nuts and lockwashers look like new after years of use too.

Tom

[Waldi]

I will try to link theory to practice:

The yield stress (YS) of an 8.8 bolt (equivalent of the 3-stripe UNF coded bolts) is 640 N/mm2.

This is the type of bolt we use in 95% of our car (although we could use lower grades in many areas). There is a limited number of exceptions, like con rod bolts.

YS SS304 bolts: 215 N/mm2.

YS SS316 even slightly lower.

There are higher strength SS bolts like A4-80 (stamped on the head) with a (minimum guaranteed) yield stress of 600 N/mm2, so simular to that of grade 8.8 bolt. A4-80 bolts can also be made from SS316, but get the higher mechanical properties from cold working (like strain hardening). The downside is this treatment increases hardness and with that the risk for stress corrosion cracking. 

The above is all theory, but what does it mean for us?

1) Be carefull when you make a modification, always consider potential side-effects. That is a general statement. In the case of bolts: Use proper (stamped) grade bolts on safety related joints like suspension, steering, brakes if you are not very familiar with this material. Mine came from a respected (trusted) supplier in the UK.

2) You can use SS bolts on less critical areas like wings (where I have SS fasteners), in the engine bay etc.

3) Be carefull galvanizing your own old bolts on high stressed locations, like the front suspension brackets to the chassis. You can use those bolts on non-critical locations.

4) Use a known-to-be-good torque wrench where the manual indicates a torque if you do not have the “feel”, especially  for safety critical connections.

Waldi

Edited May 10, 2019 by Waldi
Removed confusing information

[michaeldavis39]

Confused now, I've read on this forum that it was OK to zinc plate nuts and bolts provided they are put in the oven afterwards to heat treat them now someone is saying they shouldn't be galvanised which is same process isn't it?? 

Confused dot com

Michael

 

 

[RogerH]

Hi Michael,

 they can be zinc plated. They can be heat treated. 

But!! if they are zinc plated they should not be put under too great a stress with an elevated temperature.

So using them on the manifold could be interesting but I think I wouldn't panic over that one.

 

Roger

[Waldi]

Sorry Michael for adding too much info.

Not relevant for this topic.

I edited my above posts.

I have galvanized bolts on my TR, but do not use old (50 year old) bolts that are galvanized as part of the restauration on positions where the load is high.

Hope this helps.

Waldi 

Edited May 10, 2019 by Waldi
Removed confusing information

[michaeldavis39]

Thank you Waldi 

[BlueTR3A-5EKT]

I recall  de-embrittling electro plated cadmium high strength steel items, like propeller hubs and lots of important fastenings, at 200 c for 8-12 hours to remove hydrogen from the material surface.

The process was part of DTD904 specification, alas cadmium plating is rarely available today.

Cheers

Peter W

PS Waldi when you say galvanized bolts do you mean coated by the hot dipped process or coated with zinc by the electo plating method? 

Edited May 10, 2019 by BlueTR3A-5EKT

[Waldi]

Hi Peter,

the risk for hydrogen embrittlement (HE) comes with electroplating. The bake-out you mention at 200 degr.C shortly after the plating is what reduces this risk. I bought my bolts/nuts from Namrick, all zinc (electro) plated. I did not even ask if they had a bake-out (or other means), Namrick will know the importance.

I also had several old parts zink plated after I grit-blasted these myself, like bonnet catch, brackets, seat runners, door locks and I did bot bother about HE with these. They are low tensile stress components.  

Regards,

Waldi