Folks, I am not best pleased. About a year ago, I thought I would replace my cylinder head studs and nuts on my venerable 850 since I've always thought that I was over-doing things when checking the previous cylinder head nuts with a torque wrench. Since an 850 is not considered to be a high performance machine, I went with the standard set, described as "top grade", from a reputable parts supplier. Upon fitment, I was very pleased. The nuts felt comfortably tight at 40 ft lbs torque, and I thought everything was fine. Today, I thought I would recheck tension since I had occasion to remove the rocker cover for some other reason anyway. Imagine my surprise when one of the studs started turning around at only about 10 ft lbs. Close inspection showed the problem was "down the bottom" and not at the nut. There was nothing for it but to take the head off. And, there it was, the stud virtually snapped off in my fingers. Since the front row of studs go into the water jacket, it is my custom (which I hope is OK) to put a little bit of hylomar on the thread and only nip the stud into the block just past finger tight. Luckly for me, the broken off bit was loose enough to be unscrewed with the tip of a screwdriver. But unfortunately, the top part of the block thread has now been sheared off and will require a helicoil. I might as well do the front row since one of the other studs also looks doubtful. Have I done something wrong? Should I have gone for the more expensive Nickel Chrome Moly etc kit? Is it possible to actually buy anything of quality any more? PS: As expected, that other stud broke off after I had removed the head and was undoing it with a stud remover. It seems even finger tight was too much....

I've seen this problem with cheap studs.
If you can't justify ARP ones, I have found the Minispares competition set to be good. Fitted about 3 sets now and none stretched or broke.

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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.

Did you measure the stud length Vs the head thickness? Was there enough thread to tighten down? I've seen this happen many times before.

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

It's a good question. I didn't measure them, but I didn't notice anything untoward. I just had a look now and without a head gasket, there's a good 6 full threads spare - surely they woudn't stretch this much. I've now ordered the following (which claim to be identical to the ARP ones).

https://www.minisplus.com.au/classic-mi ... -long-rear
https://www.minisplus.com.au/classic-mi ... -long-rear

I suppose just as well I didn't have to lift the power unit out using a sling and bracket on the old head studs.

While waiting for my new head studs to arrive, I thought I would have a look at the problem in more detail. As many will know, the holes in the cylinder head for the head studs are somewhat over-sized. All are supposed to be 7/16" dia with the exception of the front centre hole which is smaller at 0.397" for "location purposes" according to the drawing. The nuts are high tensile, but there's nothing special about the washers for the front row of studs, they being PWZ106 which are "Plain Washer Zinc coated" 3/8 ID with a thickness of 1.8 mm. Sorry to mix up the units here, but you'll see why in a moment. No doubt you've often noticed that these washers get squashed down into the large hole in the head and this, I believe, causes uneven loading of the head stud since one side of the nut can be bearing against solid metal (the head casting) and the other side is simply pressing down the inner edge of the washer. and deforming it So, I've made some "special" shouldered washers the inner part sits in the head stud hole and the now-thicker (3 mm) outer part rests on the head upper surface. I am hopeful this will centre the stud in the hole at the top and when the nut is torqued down, things will be more evenly loaded. Hope it works. Picture below shows standard washer and the new special washer.

I have a set of ARP studs... sitting on my shelf... I've only ever used original studs, even when running 14psi of boost and 100bhp at the wheels

I bought the ARP studs with a voucher I won from one of the local V8 parts places, that was the only thing they had for me.. and I was surprised they had them!

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did I tell you that I won a trophy?

I used the ARP set. Mainly because I had read on other forums about the new studs being 'made of cheese'. You think they would engineer to at least minimum tolerance.

Ironically your original 50+ year old stretched studs would probably have been fine.

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

Hi eightfifty

I am glad you managed to get them out. Just a couple of questions for you to ponder:

If block head need helicoiling does the stud hole need enlarging ( I am just thinking about those bespoke washers)

and secondly, I am of two minds regarding the locating lip on the downside of the washers. I see your reasoning , but i would personally think a good ground washer ( thickish), so the washer doesn't distort is a better way of spreading the load . The picture of the original washer bending also makes me wonder whether it was the movement created that eventually killed the studs, or was it just inferior studs ( just trying to diagnose order of events) Best of luck getting your beast back on the road. cheers

I appreciate all your thoughts and suggestions. Still waiting on these new studs to arrive. So, I got one of the broken studs and had a go with a hacksaw - soft as butter (see picture).

The holes are already over-sized with respect to the stud diameter with the exception of the centre one which is the correct size, so the new washers just go on the outer pair either side at the front. The holes in the head haven't been modified, they are as they should be.

I did try new nuts on the old studs before purchasing the ones I've been showing here and things still didn't feel right hence my going for a new set thinking the old ones had lost their properties over the years and were just stretching. I had thought to go back to the old ones, but I can't find them and probably threw them away. Stupid thing to do really.

Blackened Chinesium. The worst unnatural mineral ever. Miserable stuff.

I've had these stretch and break at the base a few times. Four in one batch last year.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I'd leave it, if the threads below the deck are OK then you're better off leaving them alone, I usually drill out the first couple of threads anyway as it stops the threads pulling out of the block and creating Hugh spots. Pretty sure the tip on drilling out the top threads came from Vizard.

Run a 3/8 UNC tap down it and it'll be fine. Putting a helicoil in it could easily lead to more problems

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did I tell you that I won a trophy?

All my deliveries turned up today and so this job has rapidly (I hope) come to completion. I decided to recoil the front five head studs and leave the long ones at the back alone.

Apart from taking things apart and making sure all is clean, the first thing to do was to drill the over-sized holes for the recoil kit. The kit came with the required drill which was a nice touch. It also came with the thread insertion tool, and a tang break-off tool and of course, the tap.

Now, these holes have to be absolutely in the right place (because even though the actual cylinder head has over-sized clearance holes, the head gasket does not). As well, the holes have to be square with the top surface of the block, otherwise one might end up with a crooked head stud which would be most unfortunate. The only good way to do this with the block in the car is with a magnetic drill. The first picture below shows the setup.

Although the holes pass through into the water jacket, we only need to drill to the thread depth and so it is best to put a felt pen mark on the drill to indicate this, otherwise we might go too deep and hit something else down there.

Once the hole has been drilled, the drill is removed and the tap inserted into the drill chuck. This is to make sure that the tap is square and in the same place as the drill. Turing the chuck about one turn by hand will get the tap started, then the chuck can be loosened and the drill removed, and the rest of the thread cut with a tap wrench.

Dilling and tapping in cast iron is usually pretty easy as long as with the drill, the speed is kept down. If you cut cast iron too quickly, it heats up and becomes hard, and you find you'll have great diffiulty in making any progress. The magnetic drill I used had a rotational speed of about 350 rpm which worked very well.

Once the tap has done its work, the recoil insert is wound in with the tool, and then the tang at the bottom broken off with the magnetic push rod supplied. However, the magnetic push rod wasn't strong enough to actually grab hold of the tang and so all of them fell into the water jacket. That was OK because other than masking up all the cylinder bores and push rod holes, I had to fish out all the swarf with a stick magnet anyway.

I gave the new head studs (which, by the way looked far better finished than the old ones) a short spray with hylomar on the bottom threads (since they go into the water jacket and need to be sealed) and screwed them in just past finger tight.

The moment of truth came when I put the head gasket on. It wouldn't go on at first, which caused me some moments of panic, but then I realised it was just catching on one of the long studs and a little push, and down it went.

The head went on, along with all the other bits and pieces, and I am glad to say in torqued up just fine to the regulation 40 ft lb. I started filling up with water when I realised I'd forgotton about the bypass hose. Luckily the night before I'd put a small amount of rubber grease on it and when the head went on the hose slipped over the spigot and all I had to do was to tighten the clamp.

I did use the special washers I made up with the centering boss and they clipped in very nicely. So now I know the studs are all centred in the holes. Whether or not they'll sink in like the old standards ones did I don't know yet, but so far so good.

I'd like to thank the kind people at MinisPlus in Melbourne to sent me the new cylinder head studs and went to the trouble of making personal contact to discuss the job.

So, I'll leave things overnight and check tension again tomorrow before starting up. I suppose I'll spend the rest of the evening looking for those two rocker cover tube nuts that I must have put in a safe place but now cannot be found.

regards, Tony

I've contacted the people from whom I purchased my head studs and sent photos of the failed ones. Their response was that they contacted their supplier, who in turn contacted their supplier, and the message came back that "we've had a couple of reported cases". I've now set things up to measure the hardness of the old studs, and one of the new studs as shown below. Will keep you posted on the results.

I like that big magnetic drill - that'd be very handy

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did I tell you that I won a trophy?

Hi Tony,

I had an engine on the dyno 2 weeks ago. It started leaking water in the cylinder and out of the front and rear of the block while running it in, so I tried to pull the head down, backed the nut off then tried to pull it down to 40 ft lb. It was never going to get to 40 lb - you could feel it stretching. So I tried some of the others. Some made it to 40 lb.

I then refused to try and tune the engine using these head studs, so pulled the head off to find a copper gasket. I don't like these; seen too many problems (my opinion).

I changed the studs to a set of Mini Spares competition set from Karcraft and a better gasket - no problems.

I then put the studs on my Rockwell hardness tester to find they were only reading 20 to 22 Rockwell C, which is not very hard. Both the ARP and Mini Spares competition studs were 29 to 32 R C. This is where a good stud should be.

A stud made from 4140 material heat treated to 30RC is a very good stud it will have the hardness and toughness. You can get a piece of soft steel and harden it up but it will have no toughness - it will stretch or break. You only get what you pay for.

My back ground - Russell Engineering was making special high tensile studs and bolts from 3/8 dia to 2.5 ins for 40 years.

Graham Russell

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