Thanks GR for that most interesting post. I'll have to wait until next week for my measurements since I can't find the 12V power supply for my hardness tester and have had to order one. I've never had any particular problem with copper gaskets (it is an 850 after all) although I have used composite ones in the past but find getting the remains of the old gasket off rather inconvenient. The copper gasket I am using now came with a thin rubber O ring (as a separate part) which slips into the oil hole opening in the gasket which I thought was a nice idea. Of the two studs that broke, the second one did so when I was undoing the stud to take the head off to get the other one out. I am now finding that the accompanying rocker shaft studs I also purchased a while ago are not going to make it to the required torque and have spent an hour on the internet trying to find something better. Should have kept my old ones.

There is a Russell Manufacturing listed as a supplier to BMC (pistons etc) but don't know if this is the same you.

My hardness tester does not measure Rockwell, but I may be able to convert for the sake of comparison with your measurements. The output from my instrument is more aligned with Vickers hardness. I am quite looking forward to getting some numbers. I used to do this sort of thing for a living and it's nice to be able to use the method for a worthy purpose such as a head stud.

For those interested in the more scientific nature of this sort of thing, the property of "toughness" referred to by Graham above is more easily understood if one thinks of it as the opposite of being brittle. A soft material can be "soft" in the sense of not being hard, and it would yield rather than crack. A hard material can be quite hard (high yield point) but brittle. With proper microstructure, as stated by GR, a good stud is both hard and tough.

Regards
Tony

Hi Tony
Yes Tony i do the pistons for the small bore and the 1275 all the small bore ones are flat top pistons 998/ 1100.
Getting back to the studs we were the first so called small company to thread roll our studs and bolts,
If you look at the mini spares studs you will find they are a cut thread where as the ARP ones are rolled.
You can pick the difference when you pull them down, the ARP are very smooth to pull down where as the Mini Spares ones
then to bind when pulling them down, i like to give them 2/3 lb more as they do not pull down like the ARP
Graham Russell

_________________
"It's better to be not informed than ill-informed"

Just an update on those head studs. I measured the mechanical properties of both the cheap and the ARP head studs. Hardness testing involves touching the surface of the specimen with a specially shaped "indenter" - usually a diamond pyramid. Now, my hardness tester is not like Graham Russell's, it is a "nano" hardness tester and is designed to measure the hardnesses of surfaces whereas Graham's is a large scale Rockwell tester which applies a large load to the indenter and so reports hardness of the bulk specimen. To get something as close to his values as possible, I used a fairly large load for this instrument (about 100 mN). I am able to measure elastic modulus and hardness. For any steel, the elastic modulus is usually about 210 GPa, and indeed, for both head studs, I got an average of about 220 GPa with a tolerance of about 30 GPa. There is some scatter in my results because I am measuring at such a low load, the surface roughness of the specimen affects the results.

Now, for hardness, for the cheap studs, I got a Vickers hardness of about 220. Using an online converter, this corresponds to a Rockwell hardness of about 20 (Rockwell C). This is simliar to Graham's reading. For the ARP studs, I got a Vickers hardness of about 440 which converts to about 40 Rockwell C which is a bit higher than Graham's reading - because I am measuring the surface, where as he is measuring more in the bulk. It turns out that Hardness is related to the yield strength of the material (actually directly related to it) and so, with these readings, it is not surprising that the cheap head studs yielded. I will attempt to find out what the factory head stud material was and see how this compares with these readings. Quite an interesting measurement.
Tony Cripps

very interesting stuff - as I said on the previous page I'm still using original 1100S studs (no dimple in the centre), even with 100bhp at the wheels, I've never seen any evidence of weakness/stretching etc.

I'd be really keen to know what the hardness of an original stud was when it was new v's what it is now after 50+ years and several rebuilds

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did I tell you that I won a trophy?

Standard cylinder head studs are strength grade W steel. The dimpled ones are strength grade X.

Strength grade W steel has a hardness of 311 to 375 measured by the Brinell method. Using a converter, this corresponds to 33 to 41. I measured 20 on the cheap studs, and 40 on the ARP studs.

This means that the “cheap” studs are way below specification.

The ones with the dimple are harder again at about 38-43 Rockwell C.

The ARP ones are measuring to specification. The cheap ones will be going back to the supplier tomorrow with a request for a refund.

This is a great thread.

In my recent 1098 engine rebuild i though i would be smart and purchase new head studs rather than use 50yo studs.

Fast forward a bit I have already done 2 head gaskets (in the same amount of months) the first being a Copper gasket, so we changed back to a composite gasket - which still blew out.

After pulling the head, we found that these 'top quality' head studs from a well know mini specialist had stretched at the top end. 4 of the 9 studs were up to 1mm longer than the others and have 'hour glassed'

So now I will be off to get a set of ARP studs.... Looking back, i think i would have been better off keeping the 50yo studs, i feel they would have been better quality.

_________________
1964 MORRIS 850 - POST ZOMBIE APOCALYPSE CAFE RACER INSPIRED.

https://spotify.link/D0P4KtIP2yb

1098 +0.40
266 Kent Cam
GR Flat top pistons
HS6
1.3:1 Roller tip rockers
Stupid high CR

I appreciate your interest in this topic. Lucky for you the studs failed at the top and not in the block like mine did - stripping out half the threads in the process. I am using a copper gasket and have had no trouble except for the need to thoroughly seal the helicoils and arp studs in the block to stop water leaks. I sent the studs back to the retailer along with my test results and asked for a refund. That was some weeks ago now - no response. I suppose if I don't hear from them I'll take it to Fair Trading. $100 paid, then the cost of head gaskets and specialist equipment to repair the damage. Not happy Jan. I am also sorry I didn't keep the old studs even for the purpose of doing more measurements for comparison. So far, the ARP studs have been perfect. regards, Tony

I concur with ARP studs being good. They are also straight!
Unlike 2 sets of Minispares competition studs I fitted recently....
Several were not straight enough for the head gasket to slide down, I had to loosen them and retighten afterwards.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Readers might be interested to know that the factory outer rocker studs (long) are made from a different grade steel than the inner ones (short). This is probably because the outer ones were used for attachment of the engine lift brackets which we often see in factory photos. New replacement ones are most unlikely to be made this way. I sent my "new" rocker studs back as well since they didn't do up to the required torque either. Those engine lift brackets should not be used with a chain directly but in conjunction with a bar so that they are loaded vertically. Shear loads are quite different to tensile loads for a bolt.

Please advise part number for the Mk2 Arp stud set.

Sorry, don't have a part number for a set. I've seen them advertised though (by overseas suppliers). I purchased mine as single studs from Minisplus in Melbourne which had them on their web site. For a Cooper S, in factory condition, with the special bolt, the block side thread is 5/16 18 tpi. I doubt if a "set" as such would include a special 5/16 stud for this position and I suspect people have been fitting a 3/8 x 16 stud here with no helcoil instead - which probably damages the thread. I asked someone knowledgeable about this issue, and he said that the block has a weakness in its design at this point and so a helicoil was fitted, along with reduced torque setting, to compensate.

206-4204
BMC A- SERIES 11
STUDS HSK
from Competition Products on ebay

You still need to buy the front bolt separate I got this from car kraft