What's the purpose/benefit of re-torquing a head stud? I assume you torqued them correctly when you installed the heads. What guidance does ARP give? When you torque a head stud for the first time it stretches so that it can generate a clamping FORCE and then every time a power stroke occurs the stud stretches by a slight additional amount and then returns to its previous length and provides the same clamping tension as before.

If a stud is junk and it takes a permanent set after a short while and begins to lengthen and loose its clamping FORCE then re-torquing the stud will only be a temporary fix at best and the only long term fix is to replace the stud.

If the head gasket collapses some because it can't keep pushing on the block and head hard enough with an equal and opposite pushing FORCE to counter the clamping FORCE of the studs then re-torquing the studs might help assuming the head gasket doesn't continue to collapse under the new load on it caused by re-torquing the studs.

As you've pointed out re-torquing the studs is a lot of work and there's a definite risk of causing problems were none existed to begin with. I especially think re-torquing only the center studs is a bad idea because of the same reasons of block deck distortion cited in the link I gave earlier...

"...the fasteners not only hold down the head but also PULL-UP on the block. The threads within the block may be weak. Some spots within the block are weaker than others depending upon how much metal is around them. When these weaker spots are stressed they "give" more than other areas. This can actually deform the block and dimple the deck surface a bit. This under-appreciated problem can create sealing dilemmas..."

"The more torque that is applied onto the block the more chance of distortion. This distortion is usually seen at the weakest places at the narrowest points of the bore and at the top of the cylinder. At the top of the cylinder is where the compression pressures are always the greatest and any excess distortion there will nullify any benefit of that extra clamping force. Blow-by of gasses will cause premature gasket burn through and less horsepower. "Less maybe best"."

So there's my case for leaving well enough alone. Also it's not boost pressure per se that you need to be concerned with but rather the peak combustion pressure which depends on the combination of boost pressure, the amount of fuel injected, and very critically on injection timing especially if the timing is too far advanced.

 

And a strong argument it is.

ARP gives no guidance at all, other than a recommended pre-load torque on the studs. I did shoot them an e-mail a few minutes ago asking if they recommend re-torquing or not....and weather it should be hot or cold if they do.

 

The case for re-torquing hot is that due to the differential thermal expansion between "cast iron" and "stainless steel" the studs have lengthened relative the height of the head and loosened up slightly but if you re-torque hot what actually happens is that you increase the risk of distorting the block deck because the head is cooling off the entire time you're re-torquing the studs and this results in a differential application of clamping FORCE and pulling FORCE on the block deck even though you're applying the same torque to each stud.

So if you decide to re-torque let the engine cool for 24 hours or at least overnight as has been suggested to establish terminal equilibrium and then repeat the re-torquing of the entire set of studs not just the ones you can conveniently reach.

BTW did you use a spray-on head gasket dressing?

 

The only time I have seen a "hot retorque" is for those who have fire rings.

My only reason for suggesting Cookie retorque was due to the fact he has new gaskets, which of course over time will settle.

 

WOW, That was quite the learning experience. At least the last hour reading all of this was not wasted. Scott, glad your up and running again.

Now, I gotta go wrench on mine a little...

 

I did not. I didn't have time to order the stuff you linked to, and the only thing I had handy was some Permatex spray copper, which says it can be used on heads....but I didn't fell comfortable with it.

That's what I figured. It's also why I waited 1/2 an hour between torque checks on the final stages. I'm hoping it did most, or all of it's compressing then.

Thanks Hab.

 

Before I found the link below I was going to comment that a new head gasket will compress the most in the locations where the clamping FORCE is the highest and it'll compress the least amount in the locations where the clamping FORCE is the lowest.

The locations of highest and lowest clamping FORCE are determined in part by the pattern of the studs but there's also a random component involved because a considerable amount of the torque applied to any given stud is used to overcome thread friction and the rest of the torque generates the clamping FORCE. Since thread friction varies somewhat from stud-to-stud so does the resulting clamping FORCE.

So the differential settling of the new head gasket in effect tries to even out the variations in stud-to-stud clamping FORCE and you wind up with a better uniform distribution of clamping psi pressure.

Then along comes the person who re-torques his head gasket and the second time around due to the variations in stud-to-stud thread friction he winds up generating more clamping FORCE on studs that previously had less and this causes the gasket to restart its settling at those locations and due to the fact that everything flexes and stretches a little during the re-torquing process and due to flexing caused by thermal cycles over time you might even wind up with reduced clamping FORCE on studs that previously had more and the gasket has already compressed there.

So the net effect of the re-torquing process might be to sufficiently disturb the initial differential settling of the new head gasket and wind up with a distinctly non-uniform distribution of clamping psi pressure!

PartsTrain.com - Hard to Find Auto Parts and Truck Parts - Head Gasket - Head Gasket
Felpro Cylinder Head Gasket... 1999-2003 Ford F-350 Super Duty FELPRO PERMATORQUE CYLINDER HEAD GASKET SET -- These Head Gaskets Provide An Ideal No Retorque Design, Compresses Enough At Installation To Conform To And Seal Minor Surface Imperfections While Minimizing Relaxation And Maintaining Adequate Clamping Force Over Long Time Periods, With Felpro's 1-Year Warranty

 

Those Felpro's are exactly the gaskets that were installed .

 

Yep....that's them. I upped the chip to the lowest setting yesterday, it's just drove me crazy running around stock. Running great.....roughly 200 miles so far this week.

 

Well hopefully my lengthy inputs will be a useful contribution to the general knowledge base on head gaskets but if you'd bothered to mention that you used a "No Retorque Design" head gasket to begin with my arguments and cautions about not re-torquing it could've been much shorter! However I still think there's another issue you guys need to address!

I think I found the following "quote" on PSN and it reminded me that when I experienced unexpected failures of a component on my race car I not only repaired the problem but I also racked my brains until I was satisfied that I'd fixed the root cause of the problem as well so that the same problem wouldn't cause another DNF! As can be seen below my 5 year racing career did have its moments...



"I have been riding around with a cylinder pressure transducer and an oscilloscope for the last 4-1/2 years, and consider it an indispensible tool for tuning. I absolutely will not adjust injection timing on a high-horsepower truck without the transducer installed.

People constantly talk about when the peak pressure occurs, as if that's the only thing that matters. I'll let you into a secret--the shape of the pressure curve is way, way more important that either the position of the peak or the maximum peak pressure."

 

BINGO!!!
Rang the "Bell"

Bill

 

I've been schooled today Gene.

 

I don't remember anything on the package about them being none Retorque but it must have been there some where.

 

Here's why equations are neat things to mess with and can teach everyone including me something new. What I'm referring to here is that it wasn't until I wrote the equation for PD=Piston Distance vs C*=Crankshaft Degrees that I realized a piston doesn't descend from TDC by a distance equal to 1/2 the stroke when C*=90* ATDC and I've assembled quite a few engines in my day without noticing this!

First let me clarify something regarding the quote I gave on the relative importance of the peak versus the shape of the curve for the CP=Cylinder Pressure psi vs C*=Crankshaft Degrees. The guy who said this quote which I agree with in its correct context is an engine tuner and he was referring to the fact that tuning for the best overall shape of the CP vs C* curve is more important for making HP than just being concerned about tuning for the highest peak value of the CP curve at some particular C* location.

Previously I said that it's the peak CP value that blows head gaskets and that if the CP value at any C* location exceeds the head gasket's MSP=Maximum Sealing Pressure psi which is given by MSP={clamping FORCE}/{material AREA} psi where the clamping FORCE lb is provided by the head bolts or studs and the material AREA in^2 is the area of head gasket material that's between the cylinder wall and some critical passage like for oil or coolant to flow between the head and the block then the gasket will leak combustion gas pressure to wherever the weak spot is.

The shape of the CP vs C* curve also is a consideration for blowing head gaskets because if the CP exceeds the head gasket's MSP over a range of C* values that's more likely to blow a gasket than if the CP just barely exceeds the head gasket's MSP at some particular value of C*.

The reason the shape of the CP vs C* curve is the most important factor for making HP can be seen in the two graphs below. In the first graph the green PP vs C* curve where CP is called PP=Piston Pressure is multiplied by the green PS vs C* curve in the second graph where PS=Piston Speed to get the blue piston HP vs C* curve in the first graph.

The last picture is my hand drawn diagram of the connecting rod-crankshaft journal geometry at C*=90* ATDC where the connecting rod length is L and the stroke is S. The shape of the green PS vs C* curve in the second graph is determined solely by the L/S ratio and the crankshaft RPM so the engine tuner can only impact the shape of the blue piston HP curve by carefully tuning the shape of the PP vs C* curve.

What's important in tuning for the maximum FWHP is getting a piston HP curve shape which has a maximum "average HP" value when the blue piston HP curve is averaged over the entire 90* power stroke and this in turn requires a careful shaping of the green PP vs C* curve relative to the green PS vs C* curve because instantaneous piston HP~PPxPS!

Dan you'll be seeing the "pink" Cylinder Temperature curve again when I reply to your NOx post!

 

Just to close out the saga...sort of... I did finally get a reply from ARP this evening.

"After the fasteners are installed we recommend that you let the engine
get up to operating temperature and then shut it down and do a cold
retorque. If the car is already up and running and you have not done
the cold retorque and you aren't having any problems you should be good
to go."

I'm not crazy about the "should be" part of that advice, but I've been to not quite 30 psi a couple of times this week and frankly the truck is running better than it ever has, so I'm definitely going to leave it be.