[408Stang]

I called Cometic today and inquired about the aluminum block and aluminum head combo. They stood by their statement that it doesn't require re-torquing. HOWEVER, they echoed what Joe said about it being "free piece of mind" and "won't hurt to do it".

The tech rep I talked to said they actually recommend, during the build on a engine stand, torquing the heads down, letting it sit overnight, and then retorquing them one at a time as stated in this thread. He said this also crushes the gasket and then applies the proper torque at retorque.

With all the money and time I've put in this I'm going to go ahead and do it.... Plus, it's a LOT easier on a 3-valve to get the valve covers off.

 

[jrgoffin]

The shop that did all the machining on my block has about the same viewpoint here, Mike. When I jokingly referred to the swap from the 8740 studs to the 2000's as being a "re-torque", that process could have basically been the same thing (especially since the block had sat for over a week at that point). Still it's that extra satisfaction you get from being the one behind the wrenches that did all the work on a successful project. I'm envious that this step will be much easier for you, though, so try not to rub it in too much!!

 

[RussZTT]

When I put the heads on mine, I did the "let sit for 24 hours" however, I loosened them all instead of 1 at a time. I also didn't re-torque them after a heat cycle and haven't had any issues in 5 years. However, this go around I will do it especially for a piece of mine. Plus, Ed said too. hahaha. Kidding aside, I value his opinion so it will be done.

 

[eschaider]

To add some numbers (and hopefully clarity) to what is happening we can do a quickie approximation of the block/head growth and additional squeeze it applies to the gasket.

An ARP stud for our engines is 9 inches long. The co-efficient of thermal expansion for aluminum is 0.000023 (m/m˚C) and steel is 0.000012 (m/m˚C) or about one half that of aluminum. Because these coefficients change over temperature it is not as simple as just multiplying a couple numbers. To help in the calculation we can use a calculator over on the engineering tool box website to do the work for us. Click here => Online Thermal Linear Expansion Calculator and scroll down.

When you do the calculation for a 9 inch long steel stud from 68˚F (20˚C) to 212˚F (100˚C) the answer comes back 0.0086" growth. The same calculation for a 9 inch length of aluminum comes back 0.0166" growth. When the aluminum attempts to grow 0.0166" but is constrained by a stud that only grows 0.0086" the compressible gasket between the two is further compressed and the entire assembly is put under additional stress (clamping force) induced by the limits to the allowable growth imposed by the ARP stud.

This additional squeeze that is applied to the gasket further compresses the gasket creating a new and tighter stack height for the multiple metal gasket layers. When the engine cools the gasket does not spring back. This means the next time you start the engine it is af if you did not fully torque the head studs and the gasket seal is diminished compared to what it previously was.

When you retorque the studs you restore the stud's clamping force to the head, gasket and block bringing it back to what it originally was. Additionally at the gasket's new skinnier stack height it is significantly more resistant to additional stack height reductions. The net, net bottom line is the gasket seal you originally had, has been restored for operation after the first heat cycle and retorque of the studs.

Normally on a n/a engine the gasket seal is not as fragile as a supercharged engine. Engines with very high compression and/or thin gasket webs between the cylinders like a Pro-Stock engine are n/a exceptions. They will have increased difficulty maintaining a good gasket seal. Blown engines because of their elevated cylinder pressures have consistently been among the most difficult engines to properly seal up - especially as boost levels and load increase.

Hope this adds some visibility to the mechanics behind the issue and the reasons for retorquing.

Ed

 

[04DeadShort]

Wow, I had planned to retorque my studs with no question asked. But that pretty well notarized it. As always, great job on your explanation.

 

[Eatonualive281]

Bingo

 

[BlueScreen]

Ed speaks the truth here (again!). For many years I had problems with head gaskets seal, three I think I build and had some kind of problem there. Then, one the last one, I finally went ahead and re-torque the heads after a couple heat cycle, and a racing night (but I shouldn't have done that...). This is the first engine I have no problem at all with head gasket seal. It really just work, in theory and in practice. I will do it on all engine build from now on.

 

[04DeadShort]

Here's a crazy question. How much could the sun heat a engine up if it passed over it for a day. I know the metal body of a car can very easily burn the skin. I live in the south and mid summer days is brutal with the humidity. I guess the obvious answer is to buy a infrared thermometer and set some aluminum out. See what happens.

 

[painlessauto]

I understand the head gasket compresses further due to temperature increase thus causing a loss of clamping force when the engine cools. By re-torquing the heads you are restoring the clamping force. My question is this... After you re-torque the heads and go through a heat cycle won't the gasket suffer the same loss of clamping force as before the re-torque procedure.

 

[408Stang]

Painlessauto.... I am no metallurgy expert, but I do know a little something about physics and metal stiffness (crush) from when I was a technical accident reconstructionist. As long as you are applying the same force back to the gasket it will reach a point where it cannot crush any further without additional force being applied. Even if, during the subsequent heat cycle after retorquing the same aluminum versus steel expansion situation takes place it would have to be significantly reduced because the metal being squeezed has a new density from being crushed a couple of times already (initial install and a heat cycle) and thus a greater resistance to being crushed any further. For example... Beat on a piece of metal trying to make it flat. At some point to get it any flatter or change its shape you either have to apply more force, apply heat, apply force from a different direction, etc.

I re-torqued my heads tonight to the recommended 90 ft. Lbs. I noticed that out of all 20 bolts from both sides only 3 took 90 ft lbs to remove... (yes I did them one at a time Ed) The other 17 did not make my torque wrench click when loosening them. They all snugged right back up to 90 and I have to say that the peace of mind is well worth it. It only took me about 2.5 hours to do both sides, and it cost me nothing. (sorry if that isn't very long Joe).

As far as the debate goes.... I guess I'd ask why wouldn't you do it? What's the downside except for a little bit of time?

 

[smashedheadcat]

Can't the re-torque theory be tested by checking the torque of the headstuds after a heat cycle?

Re-torquing certainly makes sense, but maybe 90ft lbs is enough to squish the stack height into a sufficiently un-squishable height. I figure the gasket manufacturer would test this before claiming that no re-torque is required.

 

[painlessauto]

Painlessauto.... I am no metallurgy expert, but I do know a little something about physics and metal stiffness (crush) from when I was a technical accident reconstructionist. As long as you are applying the same force back to the gasket it will reach a point where it cannot crush any further without additional force being applied. Even if, during the subsequent heat cycle after retorquing the same aluminum versus steel expansion situation takes place it would have to be significantly reduced because the metal being squeezed has a new density from being crushed a couple of times already (initial install and a heat cycle) and thus a greater resistance to being crushed any further. For example... Beat on a piece of metal trying to make it flat. At some point to get it any flatter or change its shape you either have to apply more force, apply heat, apply force from a different direction, etc.

I re-torqued my heads tonight to the recommended 90 ft. Lbs. I noticed that out of all 20 bolts from both sides only 3 took 90 ft lbs to remove... (yes I did them one at a time Ed) The other 17 did not make my torque wrench click when loosening them. They all snugged right back up to 90 and I have to say that the peace of mind is well worth it. It only took me about 2.5 hours to do both sides, and it cost me nothing. (sorry if that isn't very long Joe).

As far as the debate goes.... I guess I'd ask why wouldn't you do it? What's the downside except for a little bit of time?

I have a 5.4 steel block with Trickflow heads. Torque mine to 110ft/lbs so I am not too concerned with re-tourqe. This thread just got me thinking. I have ran 21# boost with no issues. This season I am running 24# with a whipple 3.4 so I figured I would ask.

 

[eschaider]

I understand the head gasket compresses further due to temperature increase thus causing a loss of clamping force when the engine cools. By re-torquing the heads you are restoring the clamping force. My question is this... After you re-torque the heads and go through a heat cycle won't the gasket suffer the same loss of clamping force as before the re-torque procedure.

The stack height reduction from the first heat cycle pretty much takes the mls gasket to it minimum stack height. After the retorque the stack height reduction from additional heat cycles is to small to matter.

Ed

 

[eschaider]

Can't the re-torque theory be tested by checking the torque of the headstuds after a heat cycle?

Re-torquing certainly makes sense, but maybe 90ft lbs is enough to squish the stack height into a sufficiently un-squishable height. I figure the gasket manufacturer would test this before claiming that no re-torque is required.

Gasket manufacturers do their level best to produce gaskets for normal use that do not require retorquing. The discussion is not a favorite topic for them. The belief is that if one manufacture does not recommend retorquing and the others do, customers will buy the gasket that does not because they do not want th aggravation of retorquing.

Real world is that most n/a engines will not require it. Most supercharged engines should absolutely do it. Our chamber pressures can be 2x or more the pressure in a n/a engine and they can be there right from the hit with a PD blower.

Ed

 

[ScottyDsntKnow]

I'm building my first modular (4V) and still making my way through reading this thread and it has been absolutely a goldmine of invaluable information. I've done pushrods before but this is a whole nother ballgame.

 

[jrgoffin]

Glad it has helped! My apologies for being a bit delinquent lately, but I'll have some pics up of the driver's side head re-torque soon enough just to keep it going. After that, I really need to get John's Vampire tapped in and then wait for all the snow in these parts to quit so I can get back out for another drive!

 

[Quicktime_GT]

Anything new? I'm ready to see some videos

 

[ScottyDsntKnow]

Glad it has helped! My apologies for being a bit delinquent lately, but I'll have some pics up of the driver's side head re-torque soon enough just to keep it going. After that, I really need to get John's Vampire tapped in and then wait for all the snow in these parts to quit so I can get back out for another drive!

It's really helped actually. Like... a lot. Makes me not so sketch about doing the degreeing myself and also good to know the 96-98 intake cams can perform so well and about the advance.

I'm on way more of a budget than you but I suppose now I have to find $600 somewhere for one of those Vampires... I will not be running a ton of power, just about 500-600 on a freshened B headed motor with a Novi 2000. Also a silver car, Steeda special edition build #48 from model year 2000 with think every available option from Steeda that year.

 

[jrgoffin]

Anything new? I'm ready to see some videos

Nothing at the moment. Still need to get the driver's side head buttoned back up, but with work and the tax deadline coming up, I've been a bit busy. There were a couple video links several pages back of the engine running if it helps - has been completely smooth. I'll try to get some more clips in the upcoming week, especially since the exhaust has a bit more of a rumble with the extra flow.

It's really helped actually. Like... a lot. Makes me not so sketch about doing the degreeing myself and also good to know the 96-98 intake cams can perform so well and about the advance.

I'm on way more of a budget than you but I suppose now I have to find $600 somewhere for one of those Vampires... I will not be running a ton of power, just about 500-600 on a freshened B headed motor with a Novi 2000. Also a silver car, Steeda special edition build #48 from model year 2000 with think every available option from Steeda that year.

Very cool - keep everyone posted. If you dive in to the degreeing process, you'll be amazed how it will fall in to place. If you do get stuck on anything, however, there is a ton of help available here. With all the insight Ed has lent to me on this project, I'm glad to pay it all forward as much as I can.

 

[na svt]

Dont forget to check your valve lash.

Valve lash needs to be checked before the heads are assembled and installed. The reason for this is that if it' too little, the valve tips need to ground.