retorquing the head gasket...

[RoyBatty]

I prefer to use a torque method similar to how I learned to install aircraft cylinders.
First, no click type torque wrench. I use a torque meter type wrench.
I then use a two stage torque sequence where in the first pass I take the bolts up to about 80% of the final torque value. And then finish up with the final torque value.
The key is to use the torque meter to maintain your pull on each fastener, until it holds steady for a 5 second count. Instead of just yanking it until it reaches the desired number and letting off.
If during the 5 sec count the fastener moves, you restart the count once the torque value is once again steady.
Works Great.

[majicwrench]

I am a huge fan of doing what the gasket maker recommends!! OR the factory manual. All this backyard engineering is not neccessary. Read the directions.
Keith

[pastaroni34]

You probably saw the Speed Channel program where they showed how torquing bolts on a destructive tester..

Nope, sounds interesting though. A while back I actually built a torque vs clamp force tester in the shop. I use a torque load cell from Mountz and a pressure load cell from Futek. The output from both is piped into the computer. I can see a live relationship between clamp pressure and bolt torque.

[manoa matt]

When the subject of bolt torque comes up, and it frequently does there is almost always a divide, whether its the connecting rod nuts, the front crank nut, or the cylinder head bolts. Some guys approach it like a Swiss watch with cleaning regimes, specific lubricants, critical step processes for tightening etc. While other guys go for a "close enough" or "this is the way I've done it and never had a problem" type approach.

What has been generally accepted by most members is the Fiat specified torque values are almost always more than what is actually needed. Front crank nut is supposed to be 181ft pounds, while Croft says 120 is more than fine. Connecting rod nuts say 54 ft pounds, while a recent thread on Mira conceded 48 was fine.

The real contention comes in when discussing cylinder head bolts. I've got 5 different Fiat manuals in front of me and there is a wide range of torque values specified (54ft pounds up to 61.5ft pounds). Yet all the bolts are M10 X 1.25 thread pitch, grade 10.9, all cylinder heads are aluminum, and all blocks are cast iron.

As Jason pointed out there is a relationship between bolt torque and the resulting clamping pressure. The main goal is to achieve a clamping pressure sufficient to seal the head gasket to the block and cylinder head. If there was a practical way to measure and confirm the clamping pressure, the torque value would be secondary. Also the use of lubricants on the bolt threads and under the bolt head have an appreciable effect on the torque and resulting clamping force.

As a rough and round number example less say hypothetically you need to achieve a clamping pressure of XXpsi and have a means of measuring it. With no lubrication on the threads and under the head you may need to torque the bolt to 61ft pounds, If you used motor oil you may need to torque the bolt to 58ft pounds, if you use the super duper special lube you only need to torque the bolt to 54ft pounds.

Unlike newer cars, our Fiat fasteners are not "torque to yield" meaning the bolts can be reused and re torqued several times before they begin to fatigue or stretch. Therefore there is a factor of safety against stretching the bolt or damaging the threads, but if you do not lubricate the threads you are lessening that factor of safety.

Now everything is fine and dandy in discussion and theory, but what happens in the real world? Lets say you chased the threads in the block, cleaned the bolt threads and lightly oiled the bolt threads and under the bolt head. You install a brand new head gasket and tighten everything down to 61ft pounds. During the torque phase the head gasket will compress to a thickness close to its ultimate final thickness, and if left overnight it may compress even more, but to a lesser extent. Now we put the engine through a few heat cycles or 500 miles and revisit the cylinder head bolts. Why do we need to re-torque them? The cylinder head bolts are clamping down the cylinder head and gasket to the block. Aluminum has a high rate of thermal expansion so as it expands it either stretches the bolts some, compresses the gasket more, or both, all of which will result in a lessened clamping force once things cool down. You need to re-torque the bolts to restore the desired clamping force.

However a new problem arises. the problem is that the bolt threads and head surface were oiled during the original torque phase, but through the heating and cooling cycles or 500 miles, the original oil has burned off resulting in dry threads and no lubrication under the bolt head. Do you just loosen the bolt a 1/4 turn then re torque it dry, or do you completely remove the bolts one at a time so you can oil the threads and bolt head?

Will the oil "varnish up" when it burns off? Will the super duper lube burn off, or stick around? How about a "no re-torque" head gasket?

Is my thinking correct, way off base, or are we all over analyzing this?

[majicwrench]

You are overthinking things. First off, lubing the bolt with some super slick stuff is going to INCREASE the likelyhood that it will stretch beyond its limit, as you will be able to turn bolt further, more clamping force, before the torque wrench reaches the proper value.
And retorqueing, if it is not figured in by the engineers that built the thing, can create too much clamping force. There has to be a certain amount of crush left in the gasket to allow for expansion as the thing heats, and the gasket has to allow the head and block to slide upon it as they expand at diff rates.

Bottom line, for me, is to do what the gasket manufactuer or OE recommends.

[pastaroni34]

I wouldn't say overthinking things. If you don't have the tools to measure it though, its all theory. There's lots of theory on the internet, most of it is rubbish. I wish you guys were local, you can come play with my tools all you want. I'd love to have a real study on these things, I just don't have time to get all the projects on my list done, and not many people care enough to investigate this one. Its not exactly free either but neither are failed headgaskets.

The more accurate the clamp pressure you achieve, the closer your setup is to the design specifications, the less chance the system will fail. Lets say it will fail 25% of the time with +/- 30% of clamp pressure. BUT it will fail 5% of the time at +/- 10% of clamp pressure and it will fail 0.5% of the time at +/- 5% of clamp pressure.

An acceptable failure rate in someone's garage might be 1 in 5 units (20%). That might not be important to some people but for the people who manufacture, assemble, and engineer these things, its of great importance. An acceptable failure rate might be 50 in 100,000 units (0.05%).

Another interesting point.. many things put on our cars these days are not manufactured to the original OE specs anymore. They've been updated and massaged over the years. This is a problem found in many industries. So in that regard, I place little importance on the original design specifications when I am no longer using original parts.

[coise]

Well Magicwrench,
The gasket manufacturer don´t tell us anything about the product they are selling.
There is a lot of different gasket outhere, are you telling us that each should be torqued differently?
Also I agree with pastaroni34 the OEM product are long gone and we are using new product with no spec given.
I think it´s up to us to figure out what´s the best for each of or engine ( which totally differ one fron each others).

To tell you the truth I don´t know anymore what should I do with my gasket...

Thanks all for your advices.

[maytag]

And retorqueing, if it is not figured in by the engineers that built the thing, can create too much clamping force. ......
Bottom line, for me, is to do what the gasket manufactuer or OE recommends.

Majic, please don't take this as any way reflective of how I view your own knowledge, as I think you know I value your opinion and what you bring here.

But I just do not understand the thinking that somehow a Fiat engineer (or Toyota, or GM, or whatever) is somehow on another plane of existence, and are to be followed blindly.
I say B.S.
These guys are just guys drawing a paycheck. Their job is more about statistical failure than "what will it take?".
Have you ever sat in an engineers' office? Or better yet, helped him assemble a specification for a product or other? It's all about CYA. it's about "let's find precedent and historical data to back up what I've drawn." It has NOTHING to do with actual measurements or calculations.

Ok... I'm exaggerating, abit.

But what I'm getting at is that just because an engineer put it in his "design" or "specification" does not mean it's the best way, or the smartest way, or even reflective of the engineer's own opinion or "gut".

What the engineer "said" is usually the LAST thing I'm concerned about. I've dealt very, very closely with several types of engineers in several different industries. Currently, I work most closely with Electrical Engineers, and let me just say that with very few exceptions, they're all idiots. Their drawings are full of mistakes and their specifications are boiler-plate exercises in CYA.
I was once an "industry-provider" member of ASE, and those guys were the same way. They didn't want to know what the calculations and testing of the product were; they wanted to know which spec it fell into so they could interchange it with something else.

Now before I offend any of the engineer-types here, let me say that there are exceptions, particularly where a passionate subject / topic comes up, like your own Fiats!

[timinator]

The discussion of head bolt torque always returns to the same point which is " when is it tight". My opinion is that the bolt is tight when it holds the same torque value every time you check it. On a Fiat it is easy to check. If there is an air injection tube in the way remove it. If you put anti seize on the injection tube threads and don't over tighten they come off easily. The term re-torquing means to back off and bring the bolt back up to torque. When using ARP I do that before the engine gets started the first time. Checking the torque only involves seeing if the bolt resists turning with the same force as used to tighten it the first time. After the engine is heat cycled no mater what is on the threads the torque gets checked with the same torque setting as when the bolt was sliding. Since the object is to clamp the head gasket, not wait and see if it blows out, why not check it? If the method used to torque the head the first time can be done so many different ways then going back and checking it the same way only makes sense. The fact that you know the bolt is not loose is worth something.

[majicwrench]

Maytag,
As always I appreciate your opinion. Yes, engineers are human, and just like in all trades, some are idiots. I certainly DO NOT hold them on a higher plane, like I said, human. But what applies here is the old saying "You can't beat a man at his trade". These guys (and gals) do this for a living, and are darn good at it for the most part. They know a heck of a lot more about it ( gaskets design, clamping force etc) than I do. Until I get a chance to work with a whole lot of Fiat engines and gaskets where I can run some controlled tests and determine what "too tight" and what "too loose" and what lubricant works best under head bolt, I am going to use the specs provided from the engine or the gasket manufacturer.
I've been in this business (auto repair) for almost 35 years now, and have learned that the best way to do repairs that work well and last a loooong time is to believe in what the factory did.
No worries if you feel otherwise.
Your fellow human,
Keith

[maytag]

Maytag,
As always I appreciate your opinion. Yes, engineers are human, and just like in all trades, some are idiots. I certainly DO NOT hold them on a higher plane, like I said, human. But what applies here is the old saying "You can't beat a man at his trade". These guys (and gals) do this for a living, and are darn good at it for the most part. They know a heck of a lot more about it ( gaskets design, clamping force etc) than I do. Until I get a chance to work with a whole lot of Fiat engines and gaskets where I can run some controlled tests and determine what "too tight" and what "too loose" and what lubricant works best under head bolt, I am going to use the specs provided from the engine or the gasket manufacturer.
I've been in this business (auto repair) for almost 35 years now, and have learned that the best way to do repairs that work well and last a loooong time is to believe in what the factory did.
No worries if you feel otherwise.
Your fellow human,
Keith

no-no, I absolutely agree with your reasoned approach to head-gasket / head-bolt torqueing.

I just always cringe whenever anyone suggest we do something just "because the engineer said so".