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WARNING: ARP stud kit 124-4003 on Rover V8!!!

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Hi there

I am really keen to keep on using ARP head studs but I have just had a very bad experience with ARP kit 124-4003 which has led me to conclude that I should stick with the original stretch bolts - unless ARP would take note of this report and produce a new kit specially for modern Rover V8 engines.

I have used ARP kit 124-4003 on a Land Rover 4.6 V8 block (alu) and almost all the studs pulled out the block when torqued to 80ftlbs as per ARP instructions. My torque wrench is most certainly correct and calibrated. I do suspect that this particular block had most likely experienced too many head fastening cycles rendering it weak as another Rover 4.6 I built with ARP studs did go well but I now consider the ARP solution most marginal for Rover V8 engines.

What I found is this:

1) the 7/16-14 coarse end thread length for the block on the supplied studs is only 22mm (7/8"). The hole in the block for this thread is 41mm (1.6") and is threaded all the way. The coarse end could thus easily be 35mm(1.4") long for minimum stress load on the block thread.

2) the fine thread end of the studs protrude 12mm (just under 1/2") above the heads (see attached pics). The fine thread is therefore 1/2" longer than what it needs to be.

3) This means that the stud lengths can remain the same but the coarse end thread should be increased by 1/2" and the fine thread should be reduced by 7/16";

4) The kit includes 2.75" studs for the older 3.5L engines which are not used on the more modern 3.9, 4.2 and 4.6L Rover V8 engines and can be deleted resulting in a more cost effective kit. (BTW, These particular studs should only have 7/8" coarse thread on the 3.5V8)

5) The original stretch bolts use 1.1" of the thread in the block (see pics)

I suspect that somewhere in the manufacturing process, the lengths of the coarse and fine threads got swopped around.

I wrote to ARP as follows:

I recommend as follows:

1) Consider making a new kit for modern Rover V8 engines (3.9, 4.2 and 4.6) as follows:

6 x long studs

14 x short studs

2) The 7/16-14 coarse end thread should be 1.4" in length

3) the 7/16-20 fine end thread need not be longer than 9/16"

4) Overall stud lengths can remain the same.

post-9531-0-38681100-1322225273_thumb.jpg

post-9531-0-96872200-1322225305_thumb.jpg

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Strange you should have had trouble, I used them on my 4.0 and torqued up fine -yes they stick up a bit, but none stripped and tightened up well.

I'm sure the coarse thread was longer than you suggest too, seemed to take ages to screw in with an allen key.

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I run ARP studs in my 4.6 and they went in fine. I have a feeling Real Steel sell 2 different ARP kits, one being cheaper so it may be that you can get the kit minus the "deleted" studs.

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My torque wrench is most certainly correct and calibrated. I do suspect that this particular block had most likely experienced too many head fastening cycles rendering it weak

So two questions for starters:

- Is your torque wrench calibrated or not? It can't be "almost", either you know it's right or you don't.

- Why do you suspect the block was weakened? Has it definitely had multiple repairs, or do you just suspect so because it broke?

There are so many things that could affect this it seems a bit of a leap to blame ARP for the failure. You can't really know that a set of standard bolts wouldn't have just pulled out this time round.

The amount of spare thread you have sticking out looks wrong to me, I'm fairly sure mine don't have that much spare on them so perhaps your kit was wrong, either containing the wrong parts or had been made incorrectly.

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- Is your torque wrench calibrated or not? It can't be "almost", either you know it's right or you don't.

Not sure where "almost" comes from. I used the word "most" :-)

- Why do you suspect the block was weakened? Has it definitely had multiple repairs, or do you just suspect so because it broke?

My suspicion that the block is weak is based on the fact that the heads on this motor had been skimmed to the extent that the Thor inlet manifold also had to be skimmed to make it fit. This meant the motor had been worked on before and these heads had been fitted at least once before (other than in the factory). There can be no other explanation as to why the studs pulled on this motor and not on the other engine I built (which definitely had not been opened before).

Gents, please understand that I'm NOT saying that these studs won't work. Like I said, they did work on the 4.6 I built for my Disco2. I am saying that I believe the amount of coarse thread to be MARGINAL and thus I consider this kit RISKY to use as is on the Rover V8, more so if the block had been subjected to previous head fitments.

I'm also saying that ARP would do well to bring out a kit for the modern Rover V8 that makes good use of the available thread in the block rather than offering a marginal coarse thread length (and without redundant studs).

Finally, I'm not knocking ARP. I like the product and the concept. I'm just trying to spare my fellow Rover V8 builders tears. That block cost me GBP430 to have inserts installed to take the torque.

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I am sure thee are 2 x kits for a V* Rover

I have a set on the 4.5 JED and the new 5.2JED and they from memory seemed different ?

They are far far superior to the std items, but what you are describing is not good, I wouold defo do a triople check on what lits are out there / different opuions ?

somethings defo not right :(

Nige

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Not sure where "almost" comes from. I used the word "most" :-)

Must be time to get my eyes tested again then :ph34r:

You say the studs don't use enough thread engagement, but I'm sure as a ratio of diameter to engagement length it's sufficient (there is some formula for this somewhere) if not exactly over-specced. There's also the manufacturing tolerances used to machine the block, the hole may be 1 3/4" deep & tapped all the way down on your block but others may not be - the blocks have been in production for decades, with different companies doing the casting & machining. The ARP kit says "Buick 215" on the box after all!

It does sound like your block has been through the mangle a bit as well, if it's had that much machining done then it doesn't seem a great leap to imagine this was a rebuild too far for it. There's then a question mark over the quality of previous work done too.

I'm not arguing about this for the hell of it, just trying to work out a bit of the science behind the failure as it seems a bit knee-jerk to blame ARP who have been doing this stuff longer than most of us have. If there's really an issue then I'm interested, as I use ARP myself.

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Interesting thread. The thing with those studs is that the fine thread pulls way more force than normal, before you start on the higher torque value. We thought there might be as much as twice the clamping force?

I suspect the studs would be better locktighted in, so they cannot rotate in the block when being tightened. That was the bit that made me twitchy :blink:

But from a pure tecky point of veiw, if the studs are too long, its a good time to counterbore the block threads, so the thread force starts below the mating gasket face.

Which I think is an olden-day method of construction to stop the top of casting breaking out?

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......

That block cost me GBP430 to have inserts installed to take the torque.

I never realised it would cost that much, I suppose as you had done other work to the block already it wouldn't have been cheaper to go for another block :(

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But from a pure tecky point of veiw, if the studs are too long, its a good time to counterbore the block threads, so the thread force starts below the mating gasket face.

Which I think is an olden-day method of construction to stop the top of casting breaking out?

^^Yes. That is probably the answer to both the coarse thread in the block and the extra 1/2" of fine thread sticking out the top. Drop the studs down by 1/2". There ought to be about 2x D of thread in the block so if you have 7/8" of thread on a 7/16" that's about right.

It won't have taken much hamfisted mistreatment with a breaker bar to stress the threads to the point of failure in its previous life. Especially if this 4.6's previous owner was trying to tighten things up to solve a suspected water issue!!

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I'm just trying to spare my fellow Rover V8 builders tears. That block cost me GBP430 to have inserts installed to take the torque.

How much!!!!

£430 to have 20 helicoils fitted?

I'm pretty sure JE charged a customer of mine £350 to helicoil every hole in his rv8 block.

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There's also the manufacturing tolerances used to machine the block, the hole may be 1 3/4" deep & tapped all the way down on your block but others may not be - the blocks have been in production for decades, with different companies doing the casting & machining.

Let's get some facts then. Those who have blocks lying around, please take the standard long head bolt and measure how far it can screw into a 3.9/4.2/4.6 block and report here please? This single aspect almost requires a thread of its own?

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I suspect the studs would be better locktighted in, so they cannot rotate in the block when being tightened.

Trouble with these forums is that there is often so much speculation going on with little substantiating facts. ARP instructions say the studs should be turned in hand tight only. I doubt very much (see now I'm speculating) that the studs rotate when torqueing the heads. This would require the studs effectively stripping the top threads.

Personally I am not concerned about the stud ripping out a chunk of block although I can see how this might happen. The forces are too localised around those threads.

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How much!!!! £430 to have 20 helicoils fitted? I'm pretty sure JE charged a customer of mine £350 to helicoil every hole in his rv8 block.

Well, this work was done in South Africa where we don't have ample supplies of Time-serts, Big-serts etc. My engineer had to MAKE his own inserts from M16 high tensile threaded rod... This took many hours of work and cost me quite a bit in the end.

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Well, this work was done in South Africa where we don't have ample supplies of Time-serts, Big-serts etc. My engineer had to MAKE his own inserts from M16 high tensile threaded rod... This took many hours of work and cost me quite a bit in the end.

That explains the cost due to all the extra work, I imagine that method would have been very expensive over here.

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Can't you import helicoils or similar? They're small and easily available to buy online etc. You can get the studs?

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Today I installed the engine...

... and found that those protruding head studs interfere with the aftermarket exhaust manifold flanges. :angry2:

@Old Hand: I certainly can import stuff, and have, but it takes a long time, freight is very costly and our banana republic currency combined with an overzealous customs authority does not help.

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"I doubt very much (see now I'm speculating) that the studs rotate when torqueing the heads."

Mine did and had me well worried. It meant i was applying movement to the ally threads, which was not what I wanted, and the whole reason for fitting studs!

I slackened and re-torqued, and all seemed to feel much better on the second pull down.

And the over length didn't foul any genuine parts, but I had to file a fair bit off my pump raft to miss the mains bolts. But thats part of the fun ao making your own sump :)

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Good news chaps!!!

I've got two, not one, TWO, responses directly from ARP!! They confirmed that the 124-4003 kit is not intended for modern Rover V8s (although I'm still uncomfortable with the 80ftlbs torque for the 3.5). One chap volunteered to see if they can find an interim solution from existing studs, whilst the other would initiate the proper R&D route and will get a 4.6 to this effect. Of course this will take some time.

I'm just very pleased (and grateful) that ARP is willing to look at the situation!! I really did not want to go back to those awful stretch bolts on the Rover V8s.

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I do believe repeated torquing cycles can cause the thread in the block to strip. I have a customer who is rebuilding his 4.6, after having several HG jobs done by another garage. One hole already had a helicoil fitted, he had to add another, chose ARP studs to minimise the risk but ended up pulling out a helicoil along with the retapped thread in the block...

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I do believe repeated torquing cycles can cause the thread in the block to strip. I have a customer who is rebuilding his 4.6, after having several HG jobs done by another garage. One hole already had a helicoil fitted, he had to add another, chose ARP studs to minimise the risk but ended up pulling out a helicoil along with the retapped thread in the block...

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I do believe repeated torquing cycles can cause the thread in the block to strip. I have a customer who is rebuilding his 4.6, after having several HG jobs done by another garage. One hole already had a helicoil fitted, he had to add another, chose ARP studs to minimise the risk but ended up pulling out a helicoil along with the retapped thread in the block...

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I do believe repeated torquing cycles can cause the thread in the block to strip. I have a customer who is rebuilding his 4.6, after having several HG jobs done by another garage. One hole already had a helicoil fitted, he had to add another, chose ARP studs to minimise the risk but ended up pulling out a helicoil along with the retapped thread in the block...

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