Head bolts replace head studs.

[bullstarz]

Very true, an equal torque across the entire head is what most engines have and good engineering practice. I have seen and know of people who reuse head bolts, even though, especially with the Stag, they can be over 40 years old and been on and off more time than a whores drawers.

I've seen one lad, to save cost, reuse stretch bolts and not be able to achieve the correct torque setting. Some of the bolts had snapped while at least one had tried to exit the alloy block (not a Stag engine).

Using new high quality studs/bolts is the right way to go when you are putting things back together, they have less chance of them failing, so less chance of going wrong in the future. The measure twice cut once sort of mentality.

[73stagman]

From what I read here there is no real need to change the studs to bolts for their operational strength or to increase the torque at which they are fitted to a standard engine. I think the reason there is a discussion on the merits of changing them is to reduce the difficulty of removing them when required. The higher torque rating means that if they do get stuck in their threads then a higher undoing force can be applied before they break. Just because they have a higher torque rating does not mean they have to be installed at a higher than standard torque.... for a standard engine.
The different metallurgy used in their manufacture leads to them being less likely to corrode and therefore less prone to the sticking issue in any case.
If higher grade material studs are available then they would also be suitable for the same reasons. The failure of the studs during removal is the prominent issue not them failing during use.
It is my guess that Stag head gasket failures are almost never attributed to stud or bolt failure but, due to the materials used in their manufacture, they become the biggest issue when replacing said head gaskets.

[jagorstag]

You're bang on there, Neil. The only reason I'm considering replacing the studs with bolts or ARP studs is to make it potentially easier to remove the heads in the future.

Cheers,
Joakim

[Ian Durrant]

From what I read here there is no real need to change the studs to bolts for their operational strength or to increase the torque at which they are fitted to a standard engine. I think the reason there is a discussion on the merits of changing them is to reduce the difficulty of removing them when required. The higher torque rating means that if they do get stuck in their threads then a higher undoing force can be applied before they break. Just because they have a higher torque rating does not mean they have to be installed at a higher than standard torque.... for a standard engine.
The different metallurgy used in their manufacture leads to them being less likely to corrode and therefore less prone to the sticking issue in any case.
If higher grade material studs are available then they would also be suitable for the same reasons. The failure of the studs during removal is the prominent issue not them failing during use.
It is my guess that Stag head gasket failures are almost never attributed to stud or bolt failure but, due to the materials used in their manufacture, they become the biggest issue when replacing said head gaskets.

Well the thread certainly started out as being about a design that might make removal easier, but the thread evolved from there. ARP made a set for the almost identical TR7 head and they did not modify the design to use bolts instead. However they did modify the short bolts with a waist in the shaft to help equalise the stretch, so they clearly thought about things and so one must ask why the premier motorsport fasteners manufacturer didn't opt for bolts. I suspect that with such a long fastener the bolt will twist much more than a stud and nut and thus give lower clamping force. A higher clamping force helps prevent combustion gases from leaking past the fire rings and has little to do with compression ratio as combustion pressure is many times higher than the simple compression pressure. Once the fire ring is breached the hot combustion gases then destroy the composite gasket fairly rapidly.

I am not a fastener expert so this is all IMHO, but for me, using a modern ceramic based anti seize (from what I have recently read it's better than nickel or copper based anti seize) is probably the best way to go because I really can't see why a bolt will be any easier to remove than a stud with a nut welded on the top. So, for me, the only argument for changing fasteners is if they can make the head gasket seal more reliable.

[73stagman]

the only argument for changing fasteners is if they can make the head gasket seal more reliable.

This is true if that is what the problem is. If the studs "allow" the head gasket to fail then they should be changed but is this the real problem?
(And I am only thinking of standard unmodified engines not engines stressed through use in motorsport which is an entirely different kettle of fish.)
I have an RV8 all bolts? and they can still have head gasket failures. The real issue with the head gasket failures is not the fixings as I understand but other more complicated cooling issues.
The higher torque rated bolts (in 12.7 SHC form!) will be stiffer and less likely to twist.... hence the higher torque rating.. and so should undo more reliably while holding the head down with a suitable force.
(BTW how many studs and bolts are there in a Stag head to block assembly? In my 10.5:1 Rover V8 there are fourteen each side! And IIRC there are three different lengths. I know this changed with later lower compression engines)

[Ian Durrant]

This is true if that is what the problem is. If the studs "allow" the head gasket to fail then they should be changed but is this the real problem?
(And I am only thinking of standard unmodified engines not engines stressed through use in motorsport which is an entirely different kettle of fish.)
I have an RV8 all bolts? and they can still have head gasket failures. The real issue with the head gasket failures is not the fixings as I understand but other more complicated cooling issues.
The higher torque rated bolts (in 12.7 SHC form!) will be stiffer and less likely to twist.... hence the higher torque rating.. and so should undo more reliably while holding the head down with a suitable force.
(BTW how many studs and bolts are there in a Stag head to block assembly? In my 10.5:1 Rover V8 there are fourteen each side! And IIRC there are three different lengths. I know this changed with later lower compression engines)

Yes I know its generally accepted that it's overheating that blows head gaskets due to warpage of the heads. That's not my (limited) experience. I had to replace both head gaskets on mine which had never overheated and indeed the heads didn't even need a skim (18 years ago now), and you don't tend to read on here of people saying they had an overheating situation and then the head gaskets went, it seems it just happens. I like that stag owners are finding solutions to issues the main stag specialist still haven't addressed. Like header tanks to keep the pump fully immersed and if you want to go a stage further an external water pump to get rid of that Achilles heal completely. If the ARP bolts/studs can make a difference (and I believe they just might) then its worthwhile discussing it. Tony Hart is selling uprated head gaskets, can those really help? what about those uprated (Cometic) gaskets *and* the ARP stuff?

[RNF]

Seems the Cometic gasket reviews I've read all center around the preparation of the head and block surfaces. And the consensus seems to be that you must also spray the gasket with copper spray; although that too is all over the board. Doesn't seem to get much love in the ricer car world, but they have many choices compared to the Stag; Cosworth seems to be the HG that gets all their praise.

John

[Bob Heritage]

Good valid points by Neil and Ian above, but for me it is the possibility of easier removal of the heads, not the prevention of possible head gasket failure. The bolts that I can get are 6 sided Alan Key heads, the ARP ones are 12point sockets which I believe are Torx Heads?. What is the opinion of the most reliable method? I would have thought the 6 sided Alan Key with a top quality socket.

Bob

[73stagman]

Good valid points by Neil and Ian above, but for me it is the possibility of easier removal of the heads, not the prevention of possible head gasket failure. The bolts that I can get are 6 sided Alan Key heads, the ARP ones are 12point sockets which I believe are Torx Heads?. What is the opinion of the most reliable method? I would have thought the 6 sided Alan Key with a top quality socket.

Bob

Another can! Pros and cons all round again. We changed some shc to torx heads at work (M6 counter sunk ones I have to say) because they wouldn't come undone! Now they do with out fail!

[73stagman]

Use good tools and good fitter practice.
Always use a lube to install them.
Always make sure you clean out the heads and ensure that the driver fits in fully to ensure the driver tool, hex or otherwise does not "cam" out...

[72BLUE]

Always use a lube to install them.....

I thought 'lube' on the thread would give a false torque reading, ie too high, so you have to be careful with oil/grease etc upon assembley?

Cheers
Keith

[73stagman]

If the threads are dry when assembled the "torque" measured is increased by the drag on the threads rather than the forces applied by the tightened bolt to the mating surfaces. The torque settings should be specified "dry" or "with lubrication"
I don't know how Triumph did it but this is how our "torque charts" are written at work.

[72BLUE]

If the threads are dry when assembled the "torque" measured is increased by the drag on the threads rather than the forces applied by the tightened bolt to the mating surfaces. The torque settings should be specified "dry" or "with lubrication"
I don't know how Triumph did it but this is how our "torque charts" are written at work.

Ahh, thats interesting! Could this be a clue as to why some Stag head gaskets fail?

I could be on to something here................ I need to think through a theory............. Does it go like this: Stag head ROM torque figures are meant to be done 'dry' but people lube the threads and therefore under-torque them?????

Ooooh! Am I on to something or not?


Keith

[Motorsport Micky]

Ahh, thats interesting! Could this be a clue as to why some Stag head gaskets fail?

I could be on to something here................ I need to think through a theory............. Does it go like this: Stag head ROM torque figures are meant to be done 'dry' but people lube the threads and therefore under-torque them?????

Ooooh! Am I on to something or not?

Keith

Ooooh not... wrong way around.

This isn't cutting edge methodology, fastenings have been developed and used like this for god knows how many years.

Lubed threads give less resistance and hence decrease the turning effort and therefore increase the final applied torque. If you buy specialist bolts follow the practices of the supplying firm ie lube if they say so.
When I fit any bolt on race engines I clean both the bolt/nut and the threaded hole in the block or engine, then lube the thread on the exterior fixing stud or bolt, and then remove the lube with a lint free cloth, ( I don't lube internal threads in the block because of difficulty in ensuring getting them clean again ) this allows enough lube to remain on the thread to give a drag free surface and a consistent torqueing action and final torque reading.
In my opinion the basic clamping action for the heads on the TV8 engine is problematical, a mixture of very long studs and nuts mixed with two different length bolts but all the fixings are to be set at the same torque ?
The methodology doesn't appear correct to me which is why I've set my head torques differently utilising different torque figures across the fixings, 40 years on we are still trying to develop a remedial system that allows consistent and reliable methods of stopping head gasket blowing and corrosion between fixings and the head to allow removal.

Micky

[72BLUE]

Ooooh not... wrong way around. Micky

Cheers Micky, I am re-thinking my theory ..................... It now goes like this: Stag head ROM torque figures are meant to be done 'wet' but people do not lube the threads and therefore under-torque them?????

Any good?

Keith