The reason for the waisted studs is because they pass through the induction tract. You could get away with straight studs although they will reduce the maximum power of the engine. That said, how often are you really needing to go over 3000 rpm? The restriction might even give you a little boost in low speed torque.
Peter
The studs on the exhaust side are shorter.
It is difficult for me to get an accurate measurement on an assembled engine, but the machine cut thickness of the head is about 3/8" less on the exhaust side, so it is safe to presume that the studs are about 3/8" shorter.
Peter’s suggestion is supported by the fact that Harry Weslake, the gas flow expert, was involved with the development of the OHV version of the 2.5 engine at Standard for sale to SS Cars. He would think of things like that.
Ok, I get all of that. I have a 1/2-16 die coming from British Tool and Fasteners. Now I’m wondering what hardness the round stock should be to make the new studs. My local engine build shop just said hardness #8 is most used but he uses #5. So then I called a local retired machinist and he says to use 4140.
I’ll try that cuz I can find that at McMaster-Carr.
Good question… One that I hadn’t given much thought to! Here’s a little bit of information…
4140 is pretty hard material, tough to cut threads in, you may break your die.
Like I said, I would make it from a Grade 5 long bolt, McMaster 91247A746
I called McMaster-Carr to cancel the rod and add the bolts and they said to just keep the rod and they’ll add the bolts to the order at the rod price. Nice people to deal with!
I think at the end of the day, Robs advice re bolts from McMaster is probably the best way forward…
But a few corrections, re the logic/engineering and metallurgy that matters…
HARDNESS is not a property that matters with cylinder head studs, any studs, or any bolts - indeed hardness can be very much counterproductive, especially if any efforts are made to harden a bolt/stud for these cylinder head applications…
The property that matters is the ULTIMATE TENSILE STRENGTH or YIELD STRENGTH, so as that term implies the strength of the steel in TENSION. When a stud/fastener has a thread and a nut applied, the rotation of the nut on the thread transmits into a tensile force on the stud or bolt - so it is trying to stretch the stud. The UTS/Yield Strength is the ability of the stud to resist stretching. When you stretch steel it goes through two stages - initially, ELASTIC stretch then PLASTIC stretch.
If the steel stays within its ELASTIC stretch capability, with load relaxed it returns back to its original length. Once the steel exceeds its maximum elastic strength, it goes into PLASTIC stretch and quickly if continued to be loaded, it fails/breaks. One a stud/bolt has stretched into Plastic range, it stays stretched, and does not return to its original length - the stud/bolt has failed, even if not stretched to breaking point. A good analogy is an ordinary rubber-band - the elastic part is obvious, but the nature of the rubber has minimal plastic capability before immediate failure.
With steel, you can vary the properties of the steel to increase the UTS of the steels ‘strength’ and period of elastic deformation before getting to plastic deformation, thus all the various quoted steel grades that unfortunately vary from country to country, and over time in each country.
Getting back to a Mark IV/V Cylinder Head stud, these were made of course to British Standards, and not USA standards which were different (albeit equivalent).
The British Standards were totally overhauled/revised during, and immediately after WW2, adopting a grading system using the Code letters A, B, C, D, E etc. A, B and C were basic grade mild and less than mild steel, as used for small fasteners 3/16" diameter and less typically, thus no requirement to have their grade physically marked on them. D was the first graded MILD STEEL, and equated to a 45-55 (British) ton yield steel, and indeed this is the grade of the overwhelming majority of studs and bolts and setscrews used in a post-war Jaguar, with bolts/setscrews having this Grade D and/or 45-55 visibly marked on the head of the bolt/setscrew. With studs, nothing obvious, so you need to refer to Jaguars Engineering Drawings to see what grade of steel is specified. Now it should be noted that High Tensile Steel (HTS) is a generic term, for something stronger (in tensile strength) than basic mild steel, indeed one bolt manufacturer called their 45-55/Grade D bolts HT (because it was stronger than the basic A, B and C grades). But later HT steel is generally regarded as something greater than 45-55/Grade D, but there are various levels of HT steel as well, some people like to say High Tensile and Very High Tensile and Ultimate High Tensile and other similar meaningless generic terms. In Jaguar properly engineered terms, they used 55-65/Grade E bolts as there next level High Tensile fasteners, and indeed even in a few places 65-75/Grade F bolts. Then in c1952/3, so of interest to XK owners, if not Mark V owners, the British Standards revised there grading letters, so now the old D 45-55 ton mild steel, was called an R 45-55 tom mild steel, and the old E 55-65 ton high-tensile steel, became an T 55-65 ton high tensile steel. UK has moved on from these gradings, and USA never had same, so you are best to rely on what the reputable Engineering suppliers have on offer, where they offer properly graded steels for bolts, setscrews and indeed studs… Don’t go to building/home hardware suppliers where you will find most bolts/setscrews are ungraded very mild and less than mild steels, more like the old British A, B and C grades…
Also bear in mind, that cylinder head studs are meant to be stretched within their ELASTIC range, as being stretched is what produces the clamping force of the head down into the gasket and onto the block, sufficiently to stop water leaks and combustion pressure leaks. So please take notice of Jaguars torque recommendations for securing all the cylinder head studs/nuts - there is of course appropriate designed in tolerance, but be aware over torquing will start to exceed the studs elastic limits, and enter the plastic range, and then failure… And corrosion in the studs, will create stress points and a reduced cross-sectional area and thus total stud strength, so both elastic limits and entry into plastic range will be compromised…
Another term used is torque to yield. Head bolts for the AJ6/16 use these, they are centre pop marked once for their first re-use and if the head comes off again the tech knows they can use them once more and if that occurs then they are pop marked a second time indicating that is the last time they can be used.
Good point: this is one of those places where I wouldn’t resort to my backyard methods.
I would make damn good and sure that the stud material was high tensile strength. I am not entirely sure that even a good quality bolt from your local FLAPS would be adequate.
Just to clarify, the bolt I suggested has a tensile strength of 120,000 pounds per square inch. To get the maximum load, the cross sectional area would be computed using the diameter at the root of the UNC or UNF threads. For a 1/2-13 bolt the stress area is 0.1416 sq. in. so the max load would be about 17,000 pounds, at which you would expect the bolt to break.
Concerning the 45-55 (British) ton yield, would that also be per square inch?
British tonne = 2240 pounds
And would the cross sectional stress area also be computed using the diameter at the root of the BSF threads?
I do not have a chart for stress areas of BSF threads. It just shows root diameters, and for 1/2-BSF it is 0.4200", so the stress area would be 0.1385 sq. in.
The max load on the bolt material would then be 16,625 pounds.
But for a waisted stud you would use the waist diameter.
Did someone say it was 3/8"?
Stress area would be 0.1104 sq in, and max load on the bolt material would be about 13,250 pounds.
Somebody can check my calculations. I’m retired and no longer paid to do this stuff, although it is kind of refreshing.
What is FLAPS? We don’t have them here.
I think you do, thinks that stands for “friendly local auto parts store”
I have seen in Australia in the last few years 2 gigantic collections of MKV parts, one was being sold, the other I think the old guy may have recently passed, but they would have studs and other needed parts sitting in the sheds,
lets hope they dont get sent to the scrapyard
The other thing I would say is that Ed Nantes would probably have contacts for these studs. I do not know if anyone on this list has contact with him, but he was still around on Oz FB Jag parts group within the last year
Bringing back memories, but see below chart that maybe better simplifies Yield Strength versus Ultimate Tensile Strength. Yield Strength is what matters, although UTS is usually quoted…
A 45-55 ton steel (British Ton is 2240 lbs, a British Tonne is metric 1000kg = 2204.6 lbs)
so yes 55 x 2240 so 123200 pounds per square inch, noting Rob’s suggestion is 120,000 psi presumably Ultimate Tensile Strength. So in real practical terms, given all the geometry equations and variables as Rob has pointed out, and being aware that British Engineering in the 1950s/60s always had very healthy safety factors that multiplied the exact theoretical calculations (Jaguar/Engine design at a GUESS, may have used x3 or x4, but don’t hold me to that - I wasn’t there). So I still think Robs earlier advice is pretty well spot on, for use with Mark IV/V Cylinder Head studs, albeit I would really need to brush up to comment about the engineering design of Robin’s AJ6/16 Head Bolts that was in a period where they had forgotten about safety factors. Suits me to talk about my era Engineering, before you needed computers for engineering design…, although I always thought my slide-rule was ‘state-of-the-art’
I always carried a circular slide rule in high school though I can’t tell you how many times I got in trouble for using it!
Yea, ya do: Friendly Local Auto Parts Store.
I never would have guessed that one. We just have LAPS here and they don’t carry 10" bolts.
Torque is related to axial force by T=dKP where d is bolt diameter and K is a friction factor (0.2 dry or 0.15 oiled or 0.18 avg) and P is axial force.
750 inch pounds = (0.50) x (0.18) P
P = 8333 pounds load on the waisted studs
So you’re well out of the range of overstressing them.
But 1100 inch pounds and well lubed would certainly ruin them.
Interestingly, the '38-'48 SPC says the waisted studs were not in the pre-war engines.
Wayne, your quote "I have a 1/2-16 die coming from British Tool and Fasteners. " may deserve more conversation, depending on your intended actions.
I do not have any 2 1/2 litre head studs as called out in your earlier thread “A bad day in the shop”. For the 3 1/2 litre Mark V engine the head studs are:
C.339 Stud, securing Cylinder Head, Plate No. H.24, No. per Unit 6
C.340 Stud, securing Cylinder Head, Plate No. H.25, No. per Unit 8.
The 3 1/2 litre head studs are 7/16"-18tpi British Standard Fine and are not 1/2"-16 British Standard Whitworth nor some other 1/2"-16.
What is correct thread specification for the threads in your 2 1/2 litre engine block?
The 2.5 and 1.5 both use 1/2" BSF head studs. The 1.5 does not have waisted studs.
My engine builder says the British engineers over thought things right after the war.
If I recall my SS history correctly, the 2-1/2 L OHV was developed from the Standard sidevalve, which had 3 rows of studs.
The 3-1/2 L was developed fresh as an OHV, not from a sidevalve engine, which is why it has only 2 rows of studs.
