Head Gasket Replacement

[wetminkey]

At 61ftlbs of torque, these factory M10 bolts have not stretched, nor are they stressed. I'd reuse them, except that the nuts will torque onto the studs FAR more accurately than bolts will torque into their threads (especially with a thread sealant). And, I can afford the $50.
Now is the time to do it, and it's basically the very reason that I am having to do this head gasket replacement again,...I never got the head bolts torqued fully (due to unnecessary friction - my gosh, go back and see the pic of them!), and the clamping force on the gasket was inadequate.
Working full-time = rush job,...but that was twenty years ago. Luckily the engine never got much running time over the years.
Now, with a pretty 'new' engine, I can get it sealed properly, and the car can begin to get out a bit! The rest of the car is now ready for it,...

[wetminkey]

So, now that things have slowed down a bit - parts are coming, weekend/holiday are over, family events calendar empty for the moment - I had time to concentrate on the task at hand,...
What an idiot,...perhaps it would be a good idea to chase the bolt holes with a HEAD BOLT! Just got done soaking with WD40 and running a bolt in by hand. They were a mess, but not anymore! Front row, passenger-side, had so much crap at the internal end of the thread that I couldn't turn it through by hand. Finished the last ~1/4" with the ratchet's help. Now a head bolt runs smoothly by hand, through each of the ten holes, without any resistance. BINGO!
I'll flush the coolant passages out the block drain once I have the water pump and head back on,...They look beautiful on visual inspection, but there's some fine crap on the floor of the passages, and that will as much out as possible.
More later,...
Todd.

[wetminkey]

Water pump installed, gasket and head in place, tensioner bearing in place,...
Head bolts thread with so little resistance that you have to lift up on them to tell if they are threading.
Stud kit should be here Wednesday, and I will install with the Loctite thread sealant that I mentioned above. I'll use my moly lube to reduce friction on the washer/nut/thread interface and torque to the specs that Allison's supplies, since it will probably not be the 61ftlbs that stock head bolts would be.
Studs do not torque dependent on the friction of the threads in the block PLUS the washer/bolt-head interface at the top, like head bolts do. They are set in place in the block, and the points of friction while torquing are reduced to the nut/washer/thread interface at the top of the stud,...and it is lubed with molybdenum. Clamping force is then torqued evenly and correctly over the entire surface of the head and gasket,...but not to the old bolt values, due to the changes in the way that the torque is applied and measured.
Best wishes for a good week!
Todd.

[18Fiatsandcounting]

Keep the story coming, Wetminkey!

Meanwhile, back in the workshop, Bryan is still clueless regarding studs vs. bolts. If you look at the frictional torsional forces on a head bolt, they are: The friction between the bolt threads and the block threads, and the friction between the bolt head (and washer) and the top face of the cylinder head. Plus the clamping force.

If you look at the frictional torsional forces on a setup with studs and nuts/washers, they are: The friction between the stud threads and the nut threads, and the friction between the nut (and washer) and the top face of the cylinder head. Plus the clamping force.

So how are these different in terms of the accuracy of the head bolts/studs torque?

-Bryan

[wetminkey]

And this is where the details become important.
The thread surface of a bolt is FAR longer than the thread surface of a nut, and the tops of the stud, nut, and washer are lubed with molybdenum, which lowers the co-efficient of friction tremendously (far more than oil, BTW).
Necessary thread sealant changes the torque vales, in addition,...but studs do not torque at the bolt threads, only at the nut threads, so sealant makes no difference to their final torque value (and if you don't clean that crap outta there before trying to torque the bolts in again, your engine will leak, like mine did!),...
Head bolt torque is measured with a clean, dry bolt, washer and threads. And is 61ftlbs. Using a stud changes all of that, and that's why the stud nuts will be torqued to a lesser value.
If you think about it, bolts 'pull' the head down toward the block threads from below, where as the stud nuts 'pull' down on the head from above, and I would guess that there must be some advantage in that, also,...
Studs,...you don't NEED 'em, but they're a darn nice option, and cheaper than a new set of bolts!
Todd.

[18Fiatsandcounting]

Makes sense, Todd, thanks for the explanation. I have just one remaining question: How do you know what torque to use for the stud/nut/washer setup, when the specification is for the original bolt/washer combo?

-Bryan

[dinghyguy]

hmmm,

some generally accepted engineering information re bolted joints.

If a nut is used, if the material is slightly softer than the stud the nut will share the load more equally between threads BUT nominally only 3 full threads actually carry the load in a nut, on a bolt or on a stud. So thinking longer engagement is better is a bit of a fallacy if the threads are all in good condition on both pieces.

in a dry clean steel connection, about 50% of the torque goes to overcoming friction between the nut and the washer. 40% is used to overcome thread friction and the remaining 10% actually produces tension in the bolt or stud.

Unlubricated bolts have about 9% higher standard deviation compared with lubricated bolts for the same preload. So lubricated bolts torqued to the same value will be closer to the same bolt elongation and preload than non lubricated bolts or nuts. However the nominal average of either is about the same.

all the above is from Shigley, a mechanical engineering text.

So what does it mean? basically both systems, studs or nuts are equivalent in the way they load and compress the head to the block. What does matter is the materials. Given that the bolt or stud must stretch and that the preload on the head must be the same for any system, if the stud material is different than the bolt material, the torque value must also be different to apply the same compression force.

all of the above ignores fatigue effects which can become important. But of more basic importance is the material choice and the nominal bolt safety factor = ratio of preload/external applied load.
In theory if you know all the material properties of the suds vs the bolts you could in fact work out which system has a higher safety factor, but that is not a function of stud vs bolt.

Having said all that i have one question, where did all the grit from the threads in the block go? Did some go in the oil passages? if so do you have any plans to flush the oil system or just change the oil after 2 hrs of operation?

cheers
dinghyguy

[18Fiatsandcounting]

That also makes sense, Dinghyguy, and I'm sure entire PhD theses have been written on torquing fasteners.

However, if it's true that you can't remove a Fiat cylinder head with studs unless you remove the engine, that fact alone would make me wary of studs. I suppose you could remove the transmission and exhaust manifold and tilt the front of the engine downward on the motor mounts, or maybe remove the motor mounts and exhaust manifold and slide the engine forward an inch or two. But still.

-Bryan

[wetminkey]

Why would you NOT be able to remove the head with the studs in place?

[wetminkey]

In addition, you missed the point about the thread length,...bolts have 1 1/2" of thread, or so, that must be threaded into that amount of thread in the block,...every inch provides THAT much more friction. The stud is FIXED in the block. ONLY the nut turns and it's threaded length is about 1/2", which significantly reduces the amount of thread to produce friction.
In addition, THAT threaded length is lubricated with molybdenum, unlike any of the head bolt friction surfaces.
Also, thread sealant does not affect torque values because the stud does not turn in the head,...
The stud kit will come with the proper torque values for the head stud nuts. It accounts for the moly lubrication,...
It's not really rocket science,...

[wetminkey]

Oh, and if you check my thread, you'll see that I used plastic plugs to close off my oil passages while I was working with the head off, and all of the crap from the head bolt threads falls into the remaining coolant left in the jacket. I'll rinse it out of the block's side drain after I've torqued the head down.

[18Fiatsandcounting]

Why would you NOT be able to remove the head with the studs in place?

At least for the Fiat engines that I've had, the face of the block tilts slightly downward from the front to the rear. If you are using bolts, removing the cylinder head simply involves removing the 10 head bolts, lifting the head up by a 1/2" or so (to clear the two locating dowels that are diagonal on the front and rear of the block), and bringing the head towards the front of the car an inch or two and then hoisting it directly upward out of the engine bay.

I have heard that the problem with studs is that you can't bring the cylinder head forward as you lift it up, and so the rear of the cylinder head assembly (probably the caps and their nuts on the rear end of the two cam housings, or maybe the cylinder head itself) hits on the rear of the engine bay after you raise the cylinder head 2 or 3 inches, and so you're stuck because you need to lift it more than that to clear the studs. Where it hits could be the "frame" crossmember that goes across the engine bay, or the bundle of wires beneath it, or the welded attachment point for the hood latch mechanism. But somewhere.

I'm not arguing against studs, by the way. Just trying to understand how this all works in case I decide to go this route myself. One quick test would be to put two studs in the block (perhaps the two in the rear) and see if you can lay the head on the block. If you can, then you would certainly be able to take it off again with no issues.

-Bryan

[wetminkey]

I think I see what you mean! With studs in place, you would have to lift the head over the ends of the studs,...and the cowl gets in the way,...!
The studs remove as easily as they insert,...all they have setting them into the block is thread sealant,...just like bolts.
Got the head studs today, and I find that they use a 14mm, 12pt nut (far smaller, and a lot less friction, than the stock 17mm bolthead), and lubed with light oil for a final torque of 54ftlbs. A little different than the ARP stud nuts,...
The Loctite Head Bolt and Water Jacket Sealant 1158514 will be here tomorrow,...hard to get, but the perfect stuff! I'll install and torque then.
BTW, I'll install these with the head in place. And noting Bryan's point, if I need to remove the head, I'll remove the studs first.
I'll just always remind everyone to chase those head bolt holes before re-assembly. Missing that detail got me to here!
Manyana,...

[18Fiatsandcounting]

Sounds like a plan! I checked on the two Fiats I currently have ('69 and '71 spiders) and yes indeed, it would be the nuts and studs on the camshaft housing end caps that would be the issue. They would hit the "crossmember on the cowl" (for lack of a better term) if you tried to lift the head straight up and off.

Removing the studs as you suggest would work, and another option would be to remove the camshaft housing end caps and studs before trying to remove the head. Looks like it could be done, but probably not easy. Or remove the camshaft housings first, and then remove the cylinder head off the studs. This latter option might be the easiest.

I guess you could also pound in the crossmember with a large hammer to get the required clearance, but this would definitely NOT be my first choice....!

So many choices, so keep us posted on your progress.

-Bryan

[wetminkey]

Ah! Studs go in, studs come out.
1/8" Allen wrench and some thread sealant,...no more difficult than head bolts. Obviously the easy way to remove, and install, the head,...
Don't forget to chase those bolt holes!