Head studs

jp928

Well-Known Member
Couple of questions:- can you get the heads off in car with studs fitted?
Somewhere I have read that ARP studs dont use all of the block thread depth, but somebody makes studs that do, but cant find that reference now. JE? John Eales?
Anybody ?
thanks
 
Nowt wrong with ARP studs; and re-usable multiple times unlike the stock bolts which stretch, I don’t see why there’d be an issue with removing the heads, lifting these off over the studs, in a P6B. Doubt you’d experience corrosion issues either if that’s your worry. I’ve used ARP nuts/bolts/studs and never had an issue, their stuff is so good there are Fake ARP sets being sold ( ! ) so be careful of the source…

-G
 
Good to hear , thanks. Now that I re-read Hammill, he speaks of main cap studs by John Eales being a bit special, in that they are longer, and end in a cone that will bottom in the tapped block hole, for improved contact and grip. Must have confused that with head studs.
Did you use std head torque for heads on studs?
 
Good to hear , thanks. Now that I re-read Hammill, he speaks of main cap studs by John Eales being a bit special, in that they are longer, and end in a cone that will bottom in the tapped block hole, for improved contact and grip. Must have confused that with head studs.
Did you use std head torque for heads on studs?

The ARP head studs themselves are inserted with an Allen key and then only hand-tight; once the heads/gaskets are on torque the nuts up to Std. Rover spec. When I had my Rover V8 replaced it was with a cross bolted 3.9 Discovery engine, studs for the mains but retained bolts for the side fasteners, the bolts through the side of the block a “regular” P6 won’t have… using stud sets is definitely worth considering if you’ve got an engine build happening

-Graham
 
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Re this above "once the heads/gaskets are on torque the nuts up to Std. Rover spec. " -ARP notes forthe 10bolt heads call up100 ft/lbs, where std is 70ft/lbs for the P6B, but the later 10 bolt engines calls for15ft/lb then 90deg,90 deg. My 3.9 is a 1994 10 bolt.
Anybody with experience here please?
 
Re this above "once the heads/gaskets are on torque the nuts up to Std. Rover spec. " -ARP notes forthe 10bolt heads call up100 ft/lbs, where std is 70ft/lbs for the P6B, but the later 10 bolt engines calls for15ft/lb then 90deg,90 deg. My 3.9 is a 1994 10 bolt.
Anybody with experience here please?

I have never used head studs JP, so the comment that I can make is regarding your 3.9 1994 10 bolt. From your notes 15lb/ft then 90 deg, 90 deg. The bolts are initially torqued to a given figure. The two 90 degree rotations are setting a required tensile loading within the bolt. Torque and tension are quite distinct. The rotations stretch the bolt, resulting in permanent elongation. These bolts are one use only.

Ron.
 
Understand the 'stretch' bolts are single use Ron, and why. Was trying to elicit a response/comment on the difference between the original torque and ARP's figure. Somewhere in this forum I have seen somebody quote using 80ft/lb on studs, a little above the std 70ft/lb.
 
Understand the 'stretch' bolts are single use Ron, and why. Was trying to elicit a response/comment on the difference between the original torque and ARP's figure. Somewhere in this forum I have seen somebody quote using 80ft/lb on studs, a little above the std 70ft/lb.

The difference that I see JP is with the original Rover class 8 (imperial) bolts (fasteners), the tension that is experienced by the bolt is transferred into the threaded aluminium block. The aluminium threads within the block experience a shear force as a result. In the case of the stud, the aluminium thread within the block experiences very little shear force by comparison. Indeed, the nut that is tightened onto the stud is now experiencing the applied force, not the aluminium threads. This allows the high tensile steel nut to be tightened with an increased torque compared to the torque that can be safely applied to the original bolt screwing into aluminium.

Ron.
 
The plot thickens. Roverparts.com have a copy of ARP install notes dated 6/1/12, and I found another version on the ARPweb site (for the same kit, 157-4301) dated 12/1/16. The install sequence is different , as are the torques - 12 version just says 100 ft/lb, where the 16 version says 3 stages -25,50,70 ft/lbs. 12 says install the studs, then gasket and head, tighten; 16 says install gasket, head, then screw in studs, tighten. Since the 10 bolt fittings were all composite gaskets (AFAIK ?), and I plan on using these, now very happy to find the lower torque documented.
Re the advantages of studs, Ron, why wouldnt the nut and the block thread share the shear load - the block threads need to resist the load being applied by the nut? There being more threads in the block than in the nut, the load would be more spread out than in the nut.
 
The 10 bolt heads were all designed for composite gaskets as you thought JP. There is a non linear relationship between tension and shear in either a bolt or stud. I will need to double check this with a mechanical engineer (Peter, can you confirm please?) but it is my understanding that normal shear force is not evenly distributed through the threads. The first thread carries the most shear and the sixth thread the least. Female threads are stronger than male threads for the same material. That is why the bolt or stud threads will suffer shear failure (strip) before the female threads within the nut.

Ron.
 
Thanks Ron. Does the part about uneven shear loads on threads mean that there is limited value in having more than 6 threads engaged?
 
I don't have a copy of the Australian Standard AS1111 covering fasteners in front of me, but I have seen figures ranging from 1 to 1.5 times the diameter. So the number of threads that will fall within that distance. Typically anything more than 6 threads engaged serves no purpose in terms of carrying shear.

Ron
 
Thanks, all useful to know. I found something on youtube that in the end came up with thread 1-38%, 2- 25%, 3 - 18%, and 7 - 0%. That would mean a 7/16-UNC stud only needs to be engaged 0.428" - seems low, but that what the physics says.
 
The difference that I see JP is with the original Rover class 8 (imperial) bolts (fasteners), the tension that is experienced by the bolt is transferred into the threaded aluminium block. The aluminium threads within the block experience a shear force as a result. In the case of the stud, the aluminium thread within the block experiences very little shear force by comparison. Indeed, the nut that is tightened onto the stud is now experiencing the applied force, not the aluminium threads. This allows the high tensile steel nut to be tightened with an increased torque compared to the torque that can be safely applied to the original bolt screwing into aluminium.

Ron.
If you apply a tensile load to a stud by tightening a nut, the reaction in the alloy thread at the other end must be the same for the loads to balance.
 
It's the process that's different not the end result. With bolts the thread is tightened in the block resulting in increasing difficulty in turning the bolt. The bolt is also wearing the aluminum as the pressure on the thread increases as you tighten it up. With a Stud there is no wear in the aluminum block as that end is screwed in gently with no load. It also stays in place when you remove the head later so the aluminum doesn't wear. The nut on the stud provides the loading force and does so without twisting the stud significantly during tightening.

There are two ways to test the tension on the stud. One is the standard torque wrench the second uses and open ended torque wrench reading the tension and a dial guage on top of the stud to measure the stretch. If you reach the stretch point before the tension point the stud is no good...
 
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