ARP head studs. Broken

[blucille]

I’ve got a 3.6 in my 83 SC.

I’ve owned the car for 6 years, I don’t drive it more than 2-3000 miles a year, had a valve adjustment right before I bought it...and mechanic gave it a thumbs up.

Owner prior to that did the 3.6 conversion. It’s been 10 years but at most 20,000 miles....both prior owners are Pelican guys.

The guy who did the swap sourced great parts, didn’t skimp in anything and he had the motor rebuilt by “one of the best guys around denver”...used ARP head bolts

On doing my valve adjustments, I found 2 nuts loose, and those two had broken head bolts.

I’m curious if this is a known thing with ARP (doubt it)...if it’s possible the “best” engine builder did something wrong.....or something else....

Anyone have some insight? I figure I can call ARP tech support just to see what they say, not expecting any freebies or warranty after all these years, just curious.

[dannobee]

Do you have a pic of the ARP stud?

[Flat6pac]

The 964 comes factory with 24 dilivar studs.
Just a thought....
Bruce

[blucille]

[reclino]

Is that head stud magnetic? If not it's probably the factory Dilavar. Easy to check.

[Henry Schmidt]

Originally Posted by blucille

Enamel coated Dilivar. 100%

[Jeff Alton]

Ok, "one of the best guys around" padded the bill... OR the seller was not forthright with you. That is not an ARP head stud.

As much as I like ARP head studs, and have used them extensively, we are going to give Henry's Supertech studs a go on our next builds that require more than factory steel studs.

As you need new ones, both of the above will work for you, do your research and make your choice.

Cheers

[reclino]

I have a set of factory Porsche steel head studs, I bought them new, cleaned them, taped off the threads, painted with VHT satin black brake caliper paint, then baked them at 200 deg for an hour. It's possible someone painted a set of ARP studs, but not likely.
Then I decided to just get the Super Tech head studs and remove one concern from my build.

[Speedy Squirrel]

ARP studs don’t come painted. The Dilavar studs would have had the rolled thread surface. Maybe ARP studs that were painted? All this “retorquing” bothers me. One wonders what torque they were using.

[dannobee]

As stated above, it's NOT an ARP stud, nor is the nut correct ARP hardware. That's why I asked for a pic.

Something fishy went on. As Henry said, it's a Porsche dilivar stud, which are known to break.

[Jeff Alton]

Originally Posted by Speedy Squirrel

ARP studs don’t come painted. The Dilavar studs would have had the rolled thread surface. Maybe ARP studs that were painted? All this “retorquing” bothers me. One wonders what torque they were using.

Still has the factory nut..... and who would waste time painting an ARP stud...

Its a factory original stud. Someone got lead down the garden path... so to speak...

[winders]

Maybe they used ARP rod bolts on the build.......

[Speedy Squirrel]

The 964 used these, according to the PET:
Always possible that someone substituted the older style Dilavar. Easy to check with a magnet.

Originally Posted by dannobee

As stated above, it's NOT an ARP stud, nor is the nut correct ARP hardware. That's why I asked for a pic.

Something fishy went on. As Henry said, it's a Porsche dilivar stud, which are known to break.

[winders]

Originally Posted by Speedy Squirrel

The 964 used these, according to the PET:
Always possible that someone substituted the older style Dilavar. Easy to check with a magnet.

Porsche says to use these now. But, when the 964 came out, there was no 993 part number head studs....much less the 993 Twin Turbo head studs.

[safe]

Originally Posted by Flat6pac

The 964 comes factory with 24 dilivar studs.
Just a thought....
Bruce

Probably only US 964 engines... ROW seams to have 24 steel head studs, but I've only touched 3-4 3.6 engines.

[blucille]

Magnet doesn’t stick.

@speedy squirrel....I don’t understand the retorquing comment ...I don’t recall any other discussion, and on this motor, I didn’t ever torque the nuts, and I don’t have an invoice for anyone previously needing to torque the nuts.

Thanks for all the insight folks. I’ll look thru the build documents I have and see what I can find. Also, the original builder says he’ll talk to the engine builder Friday and report back. Seems like there’s more to this story.

[Henry Schmidt]

Originally Posted by Speedy Squirrel

The 964 used these, according to the PET:
Always possible that someone substituted the older style Dilavar. Easy to check with a magnet.

The stud in the OP pictures is definitely a coated Dilivar stud. I've seen hundreds.
All 964 engines came with a full array of coated, smooth shank, Dilivar studs.
It wasn't until the factory noted an unusually high failure rate of these Dilivar studs that they went back to steel studs in early 993 engines. This was very short lived. Warranty issues (weeping heads) caused them to reevaluate their choice of steel and reinvented the Dilivar. This time with an all thread monstrosity that offered a slightly more aggressive clamping force and marginally reduced failure rate.

[Mark Henry]

ARP head studs have the bullet end to aid the nut being threaded on, so definently not ARP

[winders]

Originally Posted by Henry Schmidt

...caused them to reevaluate their choice of steel and reinvented the Dilivar. This time with an all thread monstrosity that offered a slightly more aggressive clamping force and marginally reduced failure rate.

Now you are just being ridiculous. The 993 Twin Turbo fully threaded Dilivar head studs work extremely well. It seems all you want to here is knock a part that threatens sales of your head studs.

[blucille]

Thanks Henry and everyone, good to know these aren't ARP.

So the consensus is these are factory 964 (circa 1989) head studs...breakage is normal, and I'm sure in time more will break. So I've got a project for next winter I suppose.

Thanks everyone.