Installing a set of heads with ARP 12-point studs. I have called ARP three times, gotten three different answers (I am really not trusting their tech support any more ). After searching this question to death on the internet I decided to pose the question here. What is the correct way to re-torque the head studs after heat cycling with a MLS gasket:

1. Just check tightness (turn clockwise to see if the nut will click the wrench) one nut at a time in tightening sequence

2. Back off some small amount (say 1/8 turn), re-tighten to correct torque one nut at a time in tightening sequence (note that the lubrication may not be the same for this case since the ARP Moly may have washed out of the nuts/washers that are under the rockers)

3. Back off one nut at a time all the way, re-apply the ARP Moly on the stud and washer and the re-tighten to the correct torque in tightening sequence

 

Someone else here probably has better info - but I dont think you need or would want to loosen any of the bolts if they have been torqued, and you dont have any leaks. I would re-check maybe with a torque wrench, but not loosen anything. My .02.

 

I have nothing to base this on other than experience and common sense, bit I would NOT loosen the nuts at all.

Think about it this way; If you loosen the nuts, you are effectivevly starting all over again. Once you loosen the nuts, you have defeated the purpose of heat cycling them.

I would just check the torque in the same order that you torqued them, and call it Miller Time

 

I will be retorqueing them by setting the torque wrench to the proper torque, and going through the sequence and checking for tightness by listening for the click. As I understand it, the retorque procedure is done to take up any slack that may have occured during the first expansion and contraction of the block/heads. Also, I wouldn't worry about the moly being washed away from between the surfaces. The nut shoulders being torqued effectively will 'seal' the surfaces and there should still be moly between the nut shoulder and washer.

As for the proper torque... In my case they torque plate honed the cylinders with the studs in there to 70lb/ft. and 22lb/ft. So that is the torque setting I will be using.

 

Understand all the above, but the question in my mind is once the nut is tightened to the final torque value on initial installation that when you re-check you must now overcome static friction thereby obtaining a different result than if the nut were moving when you reached the final torque value.

 

I understand the question now Bob. I don't have a definitive answer but my thoughts on this are I don't think that matters much. My reasoning is the torque value that is recommended is really a range. There is error in your torque wrench and that error is most likey more than what is required to overcome the static clamping force on the nut. I don't think you are going to get within 10% of the specified torque for the fastener. It is probably more important that they all be torqued in the proper sequence and as even as you can get, within reason of course.

What I'm saying is, if you set your torque wrench to 80ft/lbs and the actual torque applied is 78 ft/lbs. I won't make much difference. What is more important is that all the nuts recieve that same 78 ft/lbs. in the proper sequence.

When I torqued my heads on recently I followed the recommended procedure. 22 ft/lbs, then 50 ft/lbs, then 70 ft/lbs. Then I went over the whole sequence at 70 ft/lbs again, and found the first 4 needed additional tightening to get to 70 ft/lbs. Then I re-did it a second time and they all clicked without moving.

 

I feel your pain on this one. When using torque to preload a bolted connection, most of the torque is lost to friction. So, as you pointed out, perhaps the faces should be re-lubed when retorquing in order to get accurate bolt stretch? In my mind, torquing is a lousy way of preloading fasteners. In fact, Machinery's Handbook states that toruque produces preload accuracy within +/- 25%, not very accurate when you think about it. But how accurate does it have to be? Evidently not very, otherwise another method would have been prescribed for preloading your studs.

I don't have any scientific basis for this recommendation, but I would retorque by tightening only - don't loosen first and then retighten.

Let us know what you end up doing.

 

I'm sure everyone has an opinion on this. A friend of mine reasons his breaking the nut/bolt loose and re-torquing as this:

Before he breaks the nut (He's using head studs) loose, he mark the nut and the head as a point of reference. He then breaks the nut loose and re-torques it. After the nut is re-torqued, he checks the mark on the nut against the mark on the head. Usually the mark on the nut is turned past the mark on the head.

When he does this, it's only one nut/bolt at a time and I have witnessed the change with my own eyes. Does that mean that torque is more accurate than if you just set the torque wrench to the recommended setting and verify? I have no clue.

 

You can't obtain a different torque value other than what the torque wrench is set at.

 

Yes, to clarify what I meant was that initially during installation the nut is turning until you reach the torque value dialed into the wrench but you are measuring a running torque. Once you stop, you have to overcome any static value. Not sure how much they differ with the ARP Lube as they may in fact be very close and ARP's reason for using is consistency in measuring stretch using torque. However, if you check the torque in the tightening direction after running the motor you have to overcome the static value so you are in effect measuring something different than was measured during the original installation.

 

Pick door number two Bob!!

Back off a 1/16 or 1/8 of a turn or so (not loose) then retorque to full spec (your simply eliminating whats called breakaway torque by loosening it a bit which can skew your actual torque value/clamp load).

Do one fastener at a time in the factory torque sequence you used to tighten them.

This is best done after a few hot and cold cycles....dont bother with a retorque till you actually run the engine. Even one full warm up and time spent at operating temp is enough.....the retorque would be done after the engine completely cools off....the next day just to be sure.

Sorry I forgot to answer your PM....seeing your post reminded me!

Tony

 

Well there ya go! Its great to have such a wealth of talent at call!

 

I'm curious about stud wind-up; what is the length and diameter of the studs - if you don't mind?

 

Just checked the catalog and they don't provide the dimensions. I don't have access to mine at the moment so not sure if someone else has a set that is currently on the bench.

 

Does this get done by GM from the Factory?....Do they heat cycle a new engine few times and then re-torque? I know they use torque to yeild so it's not a direct comparison. I've done 3 different head installs with ARP bolts on different LSX vehicles over the last 4 years, and not one of them encountered any issues after initial install. No disrespect, but I don't know why this is necessary with MLS gaskets....

 

I didn't re-torque my current setup with GM MLS gaskets, but I am being extra careful with the Cometics. I have also read where others (other boards such as Supra, Mitsubishi, etc.) have heat cycled and then checked their head stud torque to find that some preload was lost on an all aluminum motor. In my situation, I will have a lot of $$$ and time invested in the new setup when it goes in, so if an extra day or two of work will help with the longevity of the installation I will take the time to do it. Also, the AFR head instructions state it should be done as well.

You are correct though, the stock head bolts are not designed to a re-torque.

 

Cometics are great..........at spraying the frame rails with coolant

Never had a problem w/ the com., but after talking to my friend in Seekonk, I stick w/ GM MLS

 

Not necessary Stan but optional for those who dont mind to take the extra time out to insure proper and equal clamping forces after things heat up and cool down and move around a bit. If your building a very high output engine with lots of cylinder pressure (blown, turbo, nitrous), IMO it would be a more mandatory move if you want to give yourself the best chance of not having any BS with head gasket failures or leaks. The time you spend only saves you the potential headache down the road....nobody else.

Seeing as I dyno most of the engines I build on an engine dyno first, the retorque procedure is very painless as the engine is sitting right in front of you with zero accessories in your way. I did have to unbolt my shaftrocker stands which were in the way but that isnt that big a deal....

Tony

PS....The "factory" doesn't do alot of the more **** aspects of a hand built performance engine building (unless were talking 427 Z06 which sees a more personal touch). The intended usage and power output of a stock engine simply doesnt warrant it.

PSS....Most N/A combinations would probably never give you a problem if you torqued it properly the first time (no retorque after cool-down), but in the event you did have a probalem you would have wished you took the time because it will eat at you wondering whether that would have helped avoid it.

 

Steve, thought you only posted based on experience?

~5k miles on my Cometics, and know of 3 other local people running them too, none have had any issues.


Oh, and get this, I'm also running the MLS Cometics with notched 862's.

According to most anyone here, or at LS1tech, that's impossible,

 

Thanks for the clarification vettenuts. It makes sense to re-torque the cometics because of the composition of the gaskets. I have always used MLS. I was spooked from using the cometics after doing a lot of research about them on the various Forums. Good luck with your latest build

Tony, I am sure that your advice is sound, and comes from many hours of engine building experience When I build my next H/C LS6, I will remember your advice

Stan