85mm Head Gaskets

[HCA]

Rohan, I may as well ask the question here as it is near topic - re ARP head fasteners: I see that most suppliers offer a stud and nut set, but one or two - eg Lotusmarques - offer bolts. I have on order a stud set from QED, but your comments would be welcome now should a you think bolts are better...

[rgh0]

Personally I prefer the studs and nuts as you're not turning the bolt in the coarse threads in the block underload and this reduces the risk of stripping the b0lt thread. You will also get a more consistent tension load torqueing the more precise fine threads on the nut and stud top.

regards
Rohan

[2cams70]

I beg to differ and prefer the ARP bolts to the ARP studs for most applications:

1. No modification to the head is required. The ARP studs are larger diameter than the original (and ARP) bolts so enlargement of the holes in the head is frequently required to accommodate them.

2. The studs are too stiff. You want a fastener with a little give that will allow the head to lift and lower slightly during thermal cycling. This places less stress on the head gasket

3. The fine thread on the ends of the studs means that the clamping load versus torque is different to the original design. The higher clamping load from studs could be beyond what the block was originally designed for. The deck face could distort and additional stress is placed on the threads in the block.

[RichardHawkins]

Hal,

As 2 cams mentions the studs are larger diameter, which I was not aware would be a problem until I tried to fit the head. Not a good time to realise you need to enlarge the holes!

Hope this helps,

Richard Hawkins

[HCA]

Thanks. New cylinder heads allegedly are suitably reamed for studs.
There is quite a bit on t’internet of bolts vs studs with the consenus falling in favour of studs. If Rohan has spent his weekends hairing around at 8k rpm with studs holding it together, I shall stick with my order as it is

[2cams70]

Thanks. New cylinder heads allegedly are suitably reamed for studs.
There is quite a bit on t’internet of bolts vs studs with the consenus falling in favour of studs. If Rohan has spent his weekends hairing around at 8k rpm with studs holding it together, I shall stick with my order as it is

This is yet another example of what works in a race car is not necessarily the best for a road car in particular.

You won't find OEM's using dumb thick studs with no give or stretch capability in their engines. The ideal fastener is one that can stretch and still maintain a constant clamping load whilst doing so. That's why OEM's use torque to yield fasteners these days.

Aluminium expands roughly 2-3 times the rate of iron when heated. When the aluminium head on your block heats up it gets bigger at a faster rate then the iron block it is attached to. All that expansion has to go somewhere. If you have dumb studs that can't stretch all that expansion has to be taken up by compressing the head gasket. If you have somewhat less stiff and smarter elastic bolts that expansion can be shared between the bolts stretching and the head gasket compressing. If you have smarter again torque to yield bolts ideally you will have all of that expansion taken up by the bolts stretching and none by the head gasket compressing.

If you compress and relax a head gasket over many cycles eventually it will lose it's elasticity and fail. A road car engine goes through many, many cool down and heat up cycles during it's lifetime. A race car much less so.

A road car has to be durable over a very long time with no attention to retightening of the head bolts. A race engine only has to last a short time before it is dismantled and reassembled.

[ceejay]

Well Mr Mechanical Engineer.
Can you tell us how much Alloy head expansion we are talking about?

My water temp gauge tells me the twink runs between 80C to 85C... I would imagine that there would be bugger all expansion at that temp... it would be minimal at least.

The last engine 1700CC twink build I did, I used ARP head bolts torqued to 65 Lbs Ft, (Yes still the old money) no fancy dancy torque to yield bolt stuff here, the head gasket I used was sourced from Larner Race Engines Melb, I believe it was the Cometic brand.

The engine is 10.5 to one Comp ratio, it runs on 98ULP, and was dynoed at 170BHP, making the S2 is a bloody fun car to drive, and can belt the ears off some of these modern so called performance cars on very twisty and winding roads.

I have just (Yes today) come back from an awesome blast in my elan, its the perfect Aussie autumn Saturday with a top day temp of 22C.

The twink was absolutely on song, but I rarely have to wring its neck, because its such a torquey engine.

The sump is equipped with a gated and baffled sump which is a great design for Historic racing, Targa Rally comp, or just a plain old fast blast along your favourite bit of lotus road.

The handling is superb with the suspension that I run, the roads in my region are the best Lotus roads you could find... and being a long weekend (Anzac Holiday) the traffic count was quite low on the sealed back roads that I drive.

And checking the engine bay on return... all normal, no head gasket leaks. (I've actually had more dramas with weeping Aluminium radiators) But that's another story.

Yes, a race engine is very different beast from a road engine, but they all go through heat cycles, head gasket failure can sometimes be attributed to the head gasket face and the cyl block gasket face not being up to scratch, IE, not being a perfectly machined flat surface.

With every engine build, its pretty simple to determine its purpose, IE, Std road, fast road, or full race, and the money spent on each type of build will vary accordingly.

And really its up to each engine building individual to determine what the quality of the build will be, and if your are not sure, consult with your engine shop.

And to be honest, while the twink is a beautiful, fantastic engine, we are not talking about power outputs such as the output from a hot, big banger Porsche engine.

[rgh0]

The original Lotus head bolts were waisted and 8.6 mm Diameter. They were replaced with larger 9.75 mm head bolts with only slight waisting around 1969 or 70. The ARP studs are 11.1 mm, the full 7/16. I dont have a spare set of ARP bolts to check their diameter.

The ARP studs will go through most head holes in most most heads OK. On some heads some of the holes have closed up over time in the middle due to the compression forces and these may need reaming out. I have had heads where the original waisted bolts could not be pulled fully out due to this and had to be screwed out cutting a thread in the bolt hole as they came up.

The design of a gasketed clamp joint has a number of factors to consider in terms of the elasticity of the head, the bolts and the gasket and the relative thermal expansion of the components.

The ARP studs are certainly stiffer than the 2 types of Lotus bolts. Lotus went to the newer bolt for a reason, maybe just cost and they were cheaper but maybe they wanted stiffer bolts, who knows ? The early 8.6 mm bolts do have a tendency for failure if reused to many times.

The modern CFM gaskets are more compliant ( less stiff in compression and with a greater elastic range) than the original Payen steel / fibre / copper gaskets and can tolerate the stiffer stud well in all circumstances that i have seen in both race or road engines. The stiffer stud also means less loss of compression on the gasket under gas pressure in the combustion chamber and less chance of leakage.

Modern cars with the very stiff MLS gaskets probably need more flexibility in the head bolts. Hence the use of slimmer torque to yield bolts.

cheers
Rohan

[2cams70]

The ARP studs will go through most head holes in most most heads OK. On some heads some of the holes have closed up over time in the middle due to the compression forces and these may need reaming out. I have had heads where the original waisted bolts could not be pulled fully out due to this and had to be screwed out cutting a thread in the bolt hole as they came up.

Whilst the studs may just pass through the original holes on some head the chances are that when you try to align the front middle upper timing cover bolt that passes through the head and into the cover below you won't be able to unless you start modifying the head by enlarging holes.

The stiffer stud also means less loss of compression on the gasket under gas pressure in the combustion chamber and less chance of leakage.

You most likely only need to consider higher than standard head clamping forces if you are dramatically increasing the BMEP of the engine (i.e the gas combustion pressure). This really only occurs if you are turbocharging or supercharging the engine. Tuning by conventional means is mainly about maintaining the gas combustion pressure over a broader and higher range of engine speeds in order to achieve more power.

I'd suggest next time you build an engine that you try using the ARP bolts rather than the ARP studs. I very much doubt you'll experience a failure and in my opinion they are better for the reasons described.

[rgh0]

I have never had any problem aligning all the head and block bolt holes using ARP studs once reaming has been done if the head holes have closed up. This is not "modifying" the head but correcting in service distortion to restore the original 9/16 inch clearance hole in the head. I have multiple heads including from low usage late Stromberg heads to some high usage early Webers and the ARP studs fit without problem in all including front cover alignment.

The stiffer ARP studs are certainly useful on a full race twin cam. I have seen coolant come out the back of a twin cam head due to loss of gasket compression at full throttle in a 190 hp twink using ARP bolts and this problem was fixed with the ARP studs.

When using a CFM gasket The original 9.75mm later Lotus bolts, the 11.0mm ARP studs and the 9.3 mm ARP bolts would all work in a road engine. I would not reuse the early Lotus 8.6mm bolts. If using the original Payen gasket I would probably use a more flexible bolt and use the Lotus 9.75mm or ARP 9.3 mm but then again i would not use this type of gasket these days in any case. I found a set of ARP bolts that I used in the spare race engine I am currently rebuilding so I now have included a photo of all 4 variations. The engine worked for many years OK with these bolts but will probably go back together with ARP studs and I will save the bolts for a road engine maybe. I still prefer to torque up a stud thats been screwed into the casting first rather than torquing a highly loaded head bolt into a casting for both reliability and tension accuracy reasons as explained previously

As i have said multiple times the design of bolted gasketed pressure joints is a complex issue. I have spent 50 years designing this type of joint in petrochemical high pressure piping operating from 1500C to -150C in all sort of materials and containing all sorts of products so I know a little about it.

I have also spent 45 years building Twincams and know a little about that also. When I need advice on what to do for my next engine build I will ask for it as i certainly don't know everything and I learn something new every day about these engines

This topic started with information I posted on sourcing 85mm head gaskets where someone ( I wonder who ) claimed previously they could not get the Cometic 85mm CFM gaskets. So I posted photos of one and of the others gaskets I had with some details of their design variation to help people make a choice. Somehow it drifted into bolting and I have provided detailed information on the bolting options available with some analysis of the design variations to also help people make a choice. I hope it's been useful but it is not compulsory to accept what I would do a relevant to any one else's personal situation

What I complete my current engine build it will be based on my own engineering analysis and the experience of myself and others ( all around the world) with this type of competition engine

cheers
Rohan

[2cams70]

I fully agree it's a complex issue Rohan. That's why you don't find OEM's using the bigger and stronger = better philosophy when choosing fasteners for their cylinder heads!!

For a race engine studs probably aren't such a bad choice given that the engine is frequently dismantled and reassembled but for a road engine I'd argue that there are better alternatives.

By the way the reason why I did not bother too much with trying to source a Cometic 85mm CFM gasket for my engine is that I needed one greater than 0.043" thickness which at the time only Gasket Solutions could supply.

At least you and others now know that there is still a good local source for custom made gaskets following the demise of HJ.

[HCA]

Sorry, it was I who attached the question of studs/bolts, as it was near topic to my ordering a head gasket, and I thought maybe a simple answer!

I shall continue with my order as is, for a Cometic compressed fibre gasket and ARP studs. What is beginning to elude me now is the exact status of new head and block manufacture! It is always 'next month'...

[alan.barker]

Imho for a road car it's best to use Bolts. If you use studs on a road car where the Head stays on for many Miles the Studs can corrode to the Head making it very difficult to remove. e.g. a good example is on "A" series Austin Engines or others that use Studs.
I agree for a Race Engine which is dismantled on a regular basis Studs maybe ok.
Alan

[rgh0]

Imho for a road car it's best to use Bolts. If you use studs on a road car where the Head stays on for many Miles the Studs can corrode to the Head making it very difficult to remove. e.g. a good example is on "A" series Austin Engines or others that use Studs.
I agree for a Race Engine which is dismantled on a regular basis Studs maybe ok.
Alan

I use nickel antisieze on all studs I fit including head studs. They will not corrode into the head when that is done. I use ARP lube on the nut on the top of the stud.

But as I have said for a road engine using bolts or studs ( except for the early Lotus bolts) does not really matter If your using a CFM gasket. If your using the original style Payen gasket I would use bolts. I would not use MLS gaskets

cheers
Rohan

[alan.barker]

Thanks Rohan,
Lots of good info.
Alan