MK V head studs

I’m in need of some head studs and a head gasket for a 1949 MK V, 2.5L engine. If you can help, let me know.


Place a wanted add in the classifieds section.

Yeah, thanks. I did that earlier today.

Seems there are no studs available. I’m thinking my only alternative is to drill out the stud hole and either tap or insert a heli-coil to fit an obtainable stud.
Has any one here done this?

Or make one. Can you give us a picture or details about it?

I’m trying to find a 1/2”-16 Whitworth (course thread) die so I can make some replacements. Any idea if studs are any special type of steel?

Forgot to add the photos. Total length is 6 3/8”.

It’s a 1/2”-16 thread which I think means Whitworth stud, not BSF.

Rob, do you know why they used “waisted studs” in the center? I’m wondering if I have to mill the new ones down to match. I don’t believe those are in a water passage because there is no deterioration or pitting on those stud which there would have been if in water for 70 years.

Do you know an old machinist? One who knows how to set up thread cutting on a lathe? It’ll be a doddle for one of those guys.

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1/2" x 16 is BSF. It has to be BSF for this specific high tensioning and must be of high tensile (HT) steel. If you want to make one from any lesser grades, you’ll get the same failure, and much earlier in the tightening action. Using say, a long Whitworth bolt or standard 1/2" rod and turning it down won’t do. Whitworth is not high tensile. I would expect too, that the waist was rolled into the stud, not cut.

This design is a trap for the unwary and is only peculiar to the 2.5L and I’d guarantee overtightening has been done many times. From an engineering approach, this tension is rated for the 3/8" part of the stud and it doesn’t matter how big the other ends are. What would have been better to avoid this confusion would have been to just use 3/8" studs. For aesthetic appearances, the nuts could still have been 1/2" sizes but with 3/8" threads. This would have been an obvious alert to the difference.

I think the section reduction was to reduce the effects of the much higher temperatures in this area of the cylinder head, by creating a small air gap. The higher temperatures increase the expansion length of the studs, which, in turn, reduces the pressure on the head gasket.

Peter L

That seems like a good but pain in the butt answer. I’m wondering if machining the new stud and the hardening it would work. I’ve no idea the differences between high tensile and hardened steel. It would all be simpler if I could find new studs!

I would make it out of a very long 1/2" bolt of known tensile strength, say Grade 5, 10" long with 8" unthreaded.
Cut off the hex head and the UNC threaded portion.
Cut new BSF threads with a die or in a lathe.
You can get a die from Moss Motors or Metric Multistandard Components.
If you are not skilled with a lathe, a machinist can do it.
16 pitch can be done in most lathes, but the thread shape is not the same as UN so you would be better to provide the die for him to finish the threads.
A waisted stud is supposed to reduce fatigue stress.
If you think of it like a spring, it can stretch a little bit more while staying within the elastic range.


Is it just the one that you have stretched? You need to confirm their integrity by measuring the diameter accurately with a micrometer or vernier about every 5mm down the shanks. There should be no variation. The failure zone is generally around the centre but can occur elsewhere if there is a local interruption in the structure.

I have a die on the way from British Tool & Fasteners. Grabbing two head gaskets from Worcester Spare Parts cuz ya never know when and if you can get another.
As for stretching the studs, I know that the one fwd of this one turned a bit with no gain on the torque wrench so I’ll replace that one also. And if I can get this figured out, I might as well replace all four of the waisted studs.
It seems that someone in the previous curating of this vehicle had a similar problem with the center row fwd stud as there is a hex bolt in that spot.
I have two lathes but just for making ordinary parts for 1930 Cadillacs. Im not trained as a machinist and have no idea if my lathes could cut 1/2”-16 threads at the correct angle or if it need a British lathe to set that up. A nearby friend is a retired machinist and might know more about the needed type of steel and could turn these for me. Plus the shop where the car is, the owner has 4 different lathes going up to 16’ long. Self taught but has no “box” to encumber his thought process! I’ll pose the question to him on Thursday. Going to take advantage of the 32” of snow we just got and go skiing tomorrow in Vermont!

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If he’s good, he’ll know how to do it!

Unlike UNF, the thread shape with BSF is 55 degrees with rounded peaks and roots.
7-702 bsf bsw.pdf (146.6 KB)

I see the 2-1/2 Liter engines have 3 different studs. Only 4 are waisted, the one in the very center is not, it is the same as all those on the exhaust side and the front center and rear center. All those on the intake side are the third type.

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Seems there are 4 waisted studs center row aft. The rest on my engine are all the same. Guess someone has been here before!

#11s are the waisted studs.

Do you know the difference between the #10 and #12 studs?