Head gasket retorquing

Goinbyyabig

Goinbyyabig

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I installed my new ported head with ZZ fab intake on my 06 cummins a few weeks ago, and was wondering about gasket crush. Upon inital installation, I torqued the head up to 150 ft. lbs. in 25 lb. increments, then loosened each one, one at a time, re-lubed head, washer, and threads, and retorqued to 150. Then I did this again, all studs, cold, before firing for the first time. So, three torques to 150, as per ARP instructions, then I put it together, fired it and drove it. After 10 or 12 heat cycles, never more than 10 lbs of boost, I did another retorque, cold, overnight, and the gasket crushed substansially, the valve lash tightened up I about .002 to .004". My question is is this normal on any retorque or is it just the new gasket settling? I used a .020 over MLS gasket (Cummins brand) from Mumau, 625's, and I bought a brand new Snap On torque wrench for this project. I also ran the studs to the bottom of the hole, hand tight, no lube, also per ARP instructions; I tried to leave them backed out half a turn but I marked a few and they bottom themselves in the hole when tightened anyways. I'm just wondering how long before I can beat on this thing, don't want to blow the gasket!! What do you all think?
 
Sounds normal, with the gasket settling. I wouldn't suspect that you will get much more crush, with the MLS gasket and no o-rings. Make sure you back off the studs one at a time, and re-lube before you retorque. I keep doing re-torques until it stops crushing, but my labor is free... LOL

Paul
 
You should be fine, MLM gaskets do not normally need retorque, and if the studs have been torqued 3 times in their life then I don’t retorque . Most of this comes from the old 12 valve days
I have never lost a head gasket, ever.
But Paul is right, your labor is free.
So if you must retorque, follow these basics rules
Never ever , with anything but a dead cold engine, no matter who's urban myth your listening to, this is just plain engineering facts.
Always use the correct lube, ARP Ultra Lube , not anti size ,
Use a good torque wrench, one that your confident with the calibrations
In addition, do not go over what the engineers call for on torque specs , they are the people with the degrees and the ones that make the fasteners .
I lot go’s in to making the best possible high performance fasteners, use them correctly and you will get the desired results


If you have any questions, give me a PM or call I talk with the engineers at ARP on a almost daily basis, I’m heading out there in the next few weeks to go thru more training
 
I did the three retorqes (or rather Harvey at J&H Performance did) and then the final one was done hot, and the valve lash changed about .005, so yes the head will sink down. Any reason not to do at least one hot? Just curious.
 
For what it is worth and some might say I'm not pushing enough boost or the timing isn't high enough for it to really matter, but I have had no retorques on my headstuds. I did the torques up to 90ft pounds and then increments of 5lbs up to 115ft lbs. I plugged the block heater in over night and then unplugged it when I went to work the next day. Came home and did the final two 5lb increments and haven't touched them since. Numerous runs with 40+psi and 24 degrees of timing..
 
I think with o-rings, I feel better doing at least one retorque and maybe two. At least one full heat cycle and a warm retorque. Seems like the oring will cruch easier when warm.
 
diesel_importer said:
may be a dumb question, but how does the valve lash change when torquing the head?
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If the head moves down a few thousandth's, that means the rockers and everything is moving down except the push tubes. Their resting on the tappets / cam and under the end of the rockers. So you've got more tension on them. Lash will change...

Always set lash after a re-torque!!
 
JQmile said:
I did the three retorqes (or rather Harvey at J&H Performance did) and then the final one was done hot, and the valve lash changed about .005, so yes the head will sink down. Any reason not to do at least one hot? Just curious.
Click to expand...

off the top of my head if the stud is hot or warm whatever and you torque it then as it cools it could be stretched over its proper tension value and become weaker. but im no engineer
 
Thanks for all the replies guys, I think i'll do another retorque when it's apart for the cam swap, unless I get a chance to do it sooner. Probably should retorque with this cam to continue monitoring crush though. I'll post results when I do another retorque.
 
The fastener manufacturers says don't retorque when warm or hot because the fastener was not designed for warm or hot steel plus torque.

The urban myth, as Greg put it, is that the head gasket will settle more when it's warm.

I'm of the opinion that although the fastner manufacturer may not agree with warm torqueing, the head gasket experts agree that warm torques get more "squish" on the gasket.

Risk breaking a stud, or risk blowing a gasket, it's your choice!

I just over torqued my stock bolts because my truck makes less than 500 and doesn't need orings, studs, or superglue!
 
Y is it that your not suppose to bottom out the stud? Like said in the first post, wouldnt it bottom out when you when tighten them?
 
Oddly enough, you can tighten them without bottoming them out. As for breaking a stud, I think I would risk a warm retorque over blowing a head gasket. The recommended torque on a stud is usually only about 80% of what it can actually take.
 
You are trying to only place the studs stress only in a stretching fashion and it will pull against the block threads with the proper engagement that way. I just ran them down finger tight and then backed them off a 1/4 turn and used an allen key to hold them there as I ran the nut down with my other hand.

Torque studs cold, no other way...
 
I would never do a retorque when hot...from an engineering standpoint as cast iron heats up the molecules expand....and vise versa when it cools. So when you torque a head hot (everything is at max expansion), what happens when it cools off? It will loose clamping force.

However, if you torque it when cold as the engine warms up the clamping force will increase...

I always do one initial torque, then one after a heat cycle, and a third one acouple weeks later. And a retorque once a year just for the hell of it. All torques are on a cold engine that has sat atleast 12hrs. Haven't lost a head gasket yet!
 
Light It Up said:
Y is it that your not suppose to bottom out the stud? Like said in the first post, wouldnt it bottom out when you when tighten them?
Click to expand...

You can keep them from bottoming out. As to the question of Y. When the stud is not bottomed out all of the force against the threads is straight up (clamping force). When a stud (or bolt for that matter), is bottomed out and then twisted, the slope of the thread then becomes a 60* inclined plane. Basically it means that the stud now has a mechanical advantage over the threads that it would not have had if it wasn't bottomed out. End result is that you can pull the threads out of the block with less torque on the nut. The other problem is that because it is a 60* inclined plane, not only is upwards force being applied to the threads, but outwards force is being applied as well. Cracks in the block can result. This force is applied even if the stud is not bottomed out, but the amount of the force is increased.

Paul
 
stud not bottomed = attempted pure tension of the fastener (desired)

stud bottomed = fastener is put in tension & torsion
 
For all those claiming to get "increased clamp-load" when the engine heats up:

1. After gasket is seated in... torque studs with engine stone cold.
2. Go warm it up and then hit all the studs again with the same torque wrench at the same torque setting.
3. Drop your jaw as the "increased clamp-load" myth is dismissed as the nut turns another 1/8th turn.


Like I stated earlier, although the ARP studs were not designed to be torqued hot and the head gasket was not designed to be torqued hot, you will achieve more clamp load/more gasket squish if you torque on a warm motor.
 
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