getblown5.9

M12x1.75 is the tap size, but be sure its a BOTTOMING tap, it has threads almost to the very end

Captain

I feel your pain. My truck has been apart for over a month thanks to lots of companys screwing me over and I dont see it getting back together for another 2. I'm also going to be doing studs and most people have said 120-125# but I think ill stick with what ARP says at 90# or wahtever. If you read in there they say there tourq rateing is for 95% or something of the strength of the stud. hope you can get it worked out.

Crimedog

I like BigBlue's idea, if a heli-coil won't do it, you can always drill it and tap it for a 14mm stud.

On a side note, how much more thread will be there by bottom tapping? I installed studs a little over a year ago but didn't bottom tap the holes, would it be safe to remove a stud one by one and bottom tap the holes, then retorque them to say 115 lbs? I only went to 100 lat time, would this disturb the headgasket?

RustyJC

Not having a dog in this fight, I've been standing back watching this and have a basic question. I have worked for a manufacturer of engines and compressors for over 33 years, with 28 of those years in technical management. We routinely use studs threaded into cast iron blocks, compressor cylinder bodies, etc. to secure power cylinders, power cylinder heads, compressor cylinder heads, etc. In virtually all cases, the nut-to-stud torque specification is totally independent of the torque specified to seat the stud into the block. In other words, just because the specified torque for the nut is, let's say, 125 lb-ft, why does it follow that the seating torque for the stud would be 125 lb-ft? If the stud is bottoming out against the block, this imposes tremendous forces where the end of the stud meets the block casting and imposes a significant preload on the block/stud threads to which the load imposed when the nut is tightened will be additive.

Why does the stud need to be torqued into the block with anything more than a seating torque sufficient to keep the stud from backing out when the nut is loosened? In our applications, we use a bottoming tap and install a lock washer in the bottom of the hole in the block against which the end of the stud rests - this, in combination with a relatively low stud seating torque, proves entirely adequate for stud retention. The stud holes in the block are drilled with a core drill bit which produces a flat bottom hole for the lock washer to seat against.

Rusty

NCTURBOS

I'm going to throw my .02 in here.

I don't have any experience with the ARP hardware for these Cummins (yet!), but I use all ARP hardware in my motors for the Turbo Buicks. I used to "over torque" the rated value on the head studs on these motors as well. But after talking to ARP at their booth @ PRI in Orlando the other year they convinced me 100% to use their spec'd torque rating, as well as using moly-lube instead of oil.

If I could explain it in a technical way I would. But after seeing examples of their R&D on their own product...

I am very surprised you have been able to get away with going 30 ft.lbs. over their rating without more problems.


K.

Don M

Hang on fellers. Justin got it.

Some of the factory threads are not very deep. The cast in block boss's are plenty deep, but the threads are not formed in the full boss depth on some blocks. So bottom tapping gives your stud more thread engagement in the block. Lessening the chance of thread pull out.

ARP tells us to use 96 ft lbs with moly. But it also tells us this is 75% yield. Leaving a fudge factor, if you will. I tell guys to go 115 MAX on the first cycle and then get them up to 122 ft lbs on the second re-tq. And use 122 ft lbs on every re-tq after that. In theory 122 ft lbs should be close to 100% yield of what the stud will handle.

I have tested them to 185 ft lbs in incriments of 5 ft lbs from 122. The short studs for the 12 valve will live through it. The longer ones will permanantly stretch.

So, bottom tap to get as much thread engagement as you can and dont exceed 122 ft lbs.

You can repair your ripped out thread with a Heli-Coil, no problem. I had a guy do this 3 years ago. Still goig strong.

RustyJC

Don,

What are you recommending for seating torque - to seat the studs into the block?

Rusty

BigBlue

IIRC, when you go for a retorque aren't you also supposed to loosen the nut and then retorque it? I swore I could have read that somewhere.

getblown5.9

I bottom tapped and went hand tight on the studs into the block with the allen key.

then I went around and torqued the head down, 20, 30, 60, 90, 110, warm-up, then went back to 125. and a month later I took each nut off one at a time, added more moly, and went to 125-126 again.

some people say to retorque again every other oil change...but I'm going to leave them alone. when i swap injectors again, I will spot check a few studs...if they are at 125 still im not going to touch them.

Forrest Nearing

yes, you have a moment of inertia to overcome... you should also make sure you hit your "click" on your torque wrench as you APPROACH the number!

IE, if you have to stop the wrench and go back due to the wrench hitting something, when you get back on the nut, if the wrench clicks, back it back off and do it again.

if you click at say 120ftlbs, it may take 125+ to get nut to move again... this is why you need to back off in order to re-torque.

I've got 4 total torques on my studs... initial was 120 w/ 30wt oil, got it up to temp, let it cool overnight, then 120 w/ 30wt again. next was 98ftlbs w/ moly lube, next was 120 w/ moly lube.

studs should be finger tight in the block

Forrest Nearing

I would go ahead and do a line-retorque on them... just because you get a click at 125 doesn't mean the fastener is at 125. marking the nuts and making sure they don't move is the only accurate way to make sure you're not backing off

Crimedog

So would it be ok for me to go back and retorque them a year later to 120 ft. lbs if I take each stud out and bottom tap, then apply the moly lube and torque them down? I don't want to disturb the seat on the headgasket, that's my only worry.

logskidder

YEP.........COULD NOT HAVE SAID IT ANY BETTER MYSELF

dieselfan

any reason for doing them this way? 30wt the 1st and 2nd time and moly lube the 3rd and 4th? and why 98ftlbs on the 3rd time?

thanks brian

Forrest Nearing

because I didn't have any moly lube on-hand when the head gasket let go