Well, my attempts to get a new engine for my racecar up and running are not going well. I was close (or so I thought) to firing a new 4.0L with new liners, forged pistons, TA heads, etc. When I put water in the cooling system I had leaks into the valley area that I thought was the Cometic MLS gaskets I'm using. Today I got the engine out and the heads off and found a much more dire situation, it appears I have cracks around one of the head bolts between cylinders 2 and 4. I'm certain it wasn't this way when I assembled it, it seems like the torque of the head studs caused the cracks. I used ARP studs and installed per their instructions - torqued to 100 ft-lbs total in an ascending sequence of three steps.
The block was a used take-out unit that was bored and new liners installed by a reputable machine shop (will not be named until I can resolve this issue) that has lots of experience with these engines. Has anyone seen a failure like this before? I don't think I have much alternative but to replace the block, will be calling them tomorrow to discuss.
Rover.jpg
I think you will find that head bolt torque to be excessive.
Jim
Had that thought. A little too late now unfortunately.
I only torque mine to 70lb,
FWIW, my machinist won't use ARP bolts and studs on the Rover engines. His reasoning is that they need to be torqued more than what the block can hold to be more effective than stock bolts. I have a set of used ARPs that was in an engine I sent out to be rebuilt. Didn't even know they were in there until he called me looking for a set of stock bolts. Also have a set of brand new ones that came with an unassembled engine that was part of another project. He wouldn't use those either. He installs time serts?? in the heads before they are needed as well whenever we do roller rockers or stiff valve springs for the same reason.
Now you tell us, Todd. ;)
Seriously, I have not heard that. I pulled the threads out of one of 3.9 blocks just torquing an ARP stud to right at 55 lb-ft.
I inserted double stacked helicoils in my Olds 215 block and still had problems with pulling the threads at about 50 ft/lbs of torque. (of course that was with 16 lbs of boost)
Pulling torque on those blocks always felt mushy. Moving to an iron block fixed all that.
Jim
Doug, Perhaps you can post-up, where ARP says to torque a 7/16" stud, in aluminum, to 100 ft/lbs. ? IF you torqued 7/16-14 bolts to 100 ft/lbs, that would have increased by approx. 43%, with the 20 tpi., of the studs ! I suspect you'll find the deck(s), are no longer flat. Good luck. roverman.
The ARP kit (157-4301) contains and instruction sheet with torque instructions and pattern. Looks like I can't attach a PDF but you can easily download it off their web site. Here's the key text though:
"7. Lubricate the stud threads, nuts and washers with ARP ULTRA-TORQUE FASTENER ASSEMBLY LUBRICANT.
Then install the washers and the nuts onto the studs and tighten them hand tight. ARP recommends using the
ARP ULTRA-TORQUE FASTENER ASSEMBLY LUBRICANT that is provided with each kit as opposed to
motor oil. This is due to higher friction on the studs as well as inconsistencies in the clamping force of
the fasteners when motor oil or other low quality lubricants are used.
PRELOAD (TORQUE) RECOMMENDATIONS
8. Following the manufacturers recommended torque sequence tighten the nuts in three equal steps to 100 ft lbs
with ARP ULTRA-TORQUE FASTENER ASSEMBLY LUBRICANT. "
I have spoken with ARP today and they are investigating. The gentleman I talked to sounded legitimately concerned and asked for photos, block info, etc. I'll report back when I hear more from them.
I think ARP owes you a block.
http://arpinstructions.com/instructions/157-4301.pdf
First, hang the "proof-reader", then argue for a new "Coscast" block,(add boot/$ as needed).
Well, it still isn't resolved but I have made progress. ARP says that they tested the factory head bolts when designing this kit and the 100 ft-lb torque spec correlates to ~10% increase in clamp load. They have sold around 600 sets of these and say this is the first cracked block they have heard of, though they did seem to acknowledge reports of thread pull-out. They are arguing that they can't be held liable for the full damage because it may be that I just have a weak block. There's another complicating factor - I got the studs through TA Performance and evidently there is some difference between the ones I have and the pure Rover kit, sounded like a slight material change. That didn't make a lot of sense to me and the gentlemen I talked to was sort of vague about it but indicated that TA should really be providing the exact Rover kit. He acknowledged though that the slight difference in stud isn't really the issue, it's the strength of the thread in the block.
They're thinking about changing the value of the torque spec or putting in some kind of warning in the instructions, but also said they might just stop selling the kit. I think that they are thinking that if they acknowledge this is a possible result then they could be liable for cracked blocks or stripped threads when it does happen.
They said they would try to help me out with the repair and I'm waiting on a call with a proposal. We'll see what happens.
Doug,
Sorry to hear of your issue. Got a question. How did ARP come up with a torque value comparison when the stock bolts are torque to yield?
100 ft-lb is a lot! It's been awhile, but if I remember correctly I think that I only went up 5% from the stock torque spec when using ARP head studs. For the bottom row of bolts it was less so that it wouldn't cock the heads.
You may want to contact Mark at D+D for more info, he's the one who gave me the torque specs and I've good luck so far even with running 9.5 to 10 psi of boost.
Bill
When one considers that the torque spec for the original BOP head bolts was 45-55 ft-lbs, 100 ft-lbs for studs does seem high!
Considering that the object of torquing the studs is to stretch them (minutely), it's really a good idea to consider the end fasteners. Top end, no problem, similar material, suitable length of thread engagement. But on the far end, that's where it gets troublesome. IIRC, typical thread engagement into aluminum is 2-1/2 times the thread diameter, minimum. But for high tensile hardened fasteners that number will have to go up, perhaps quite a lot. Maybe even double in some cases. You could need 2"+ of thread engagement before you are able to stretch the fastener. But what does that do to the deck? Even if there is enough depth of thread, is there the internal reinforcement required to prevent warpage and cracking? Apparently not in this case.
When a company sells studs without regard to the construction of the engine they go into and simply specs the diameter, length, and torque necessary to stretch the stud rather than referencing it to the original design in some way there is likely to be trouble. Were it an iron engine it would not be a problem, but aluminum has different requirements.
Jim
I would think a "weak block" would have pulled threads. The strong, sound block over-torqued? Well,,,,it cracked. Cased closed, pay the plantiff! ;)
Interesting, the ARP Buick 215 kit 124-4003 "only" has a torque setting of 80 ft-lbs, why would the 10 bolt kit need to be spec´d at 100 ft-lbs ?
I think I torqued the Merlin head bolts to 68 ft-lbs. And these are long bolts. The feeling when doing the last round is very scary, it feels like the threads will let go any minute :-)
Jukka,
Felt the same way doing the stock head bolts. 20 mm (14.7 ft lb) followed by 90 and then another 90 deg! Guess those at least stretch more easily than the ARP studs so less chance of pulling out the threads from the block. If we can calculate what the stock bolts torque number would be, Doug would have more ammunition for his battle with ARP. I have seen reports that you get around 65ft lb when turning the stock stretch bolts the final 90 deg if that helps.
Yep, I think ARP has a problem there.
I was checking last night on an old 4.6.
Correctly angle torqued the bolts show 72 ft,lbs consistently.
Measuring the thread engagement into the block shows 1.100" of engagement depth. The block is actually threaded 1.700" so lots more room for stud length
I've got 2 sets of ARP head studs in hand.
Interestingly the literature in one box says 80 ft.lbs. not 100 that other kit advertises.
Measuring the thread engagement into the block shows 0.900" which is roughly 20 percent less than the factory bolt. And far shy of the 250 percent engagement rule.
Due to the fine thread end of the stud being the torquing surface it increases the tensile force on the stud by a rough factor of 2 compared to the coarse thread of the stocker.
This means that even at the lower 80 ft,lb figure, the force pulling the threads out of the block has increased by another 130 percent.
No wonder these things pull out!
I don't think that the machine shop has any liability here at all. It would seem to rest squarely on ARP.
I use ARP stuff almost daily and have never had an issue.
But I am going to check more carefully from now on.
Live like you mean it.
Fred
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Clan, threads in block are 14 threads per inch. Threads on nut end, are 20 threads per inch. Let's do the math, 20 divided by 14 = 1.42857. In other words, if one were to torque the studs 100 ft/lbs., it would be equal to torqueing the standard 7/16-14 bolt to 143 lbs ! A lot of oem iron blocks would crack ! Doug, can you put a straight edge, on the deck, over the crack, and send us a picture ?
Thanks for all the input here guys, great discussion. I'm still talking with ARP about the issue. I'll shoot some more photos of the block today and check it with a straight edge.
Can someone do me a favor and send me dimensions of a stock head bolt (overall and thread length)? Thanks!
The stock torque to yield bolts are 7/16th" x 14 TPI.
They come in two lengths 3.770" and 2.600" with threaded portions at 3.00" and 1.750" respectively.
I know this thread goes back a couple of years, but I was wondering what the final outcome of it was?