TTY head bolts - more than you might want to know.

[TylerDurden]

I'm using new 12mm TTY bolts from AutohausAZ on a 1.6 TD.  (I did notice that some bolts were lighter/more-shiny than others.)

I read the threads on dry/oiled stretch bolts. I went dry, figuring the oil on the new bolts was to prevent rust.

No mention of oil in Bentley...

The block holes were cleaned and dry.

Only half of the bolts got to the yield-point, the others got up to ~100ft-lb and no yield.


All 12mm are TTY, yes?... Try again with oiled bolts?



Edit: revised title

[92EcoDiesel Jetta]

How did you determine whether the bolts yielded or not? I also used head bolts from Autohausaz to do the head gasket on my 92 Eco and as I recall, I cleaned the block holes out with brake cleaner, blew out with compressed air but left the oil that came with the bolts (did not clean them)and followed the Bentley torque procedure and everything came out alright, no leaks of any kind so far in 20k miles.

[TylerDurden]

Thanks for the reply.

With a beam type wrench you can see and feel the torque reach a plateau when the bolt yields... ~85ft-lbs.

[92EcoDiesel Jetta]

I used a click type torque wrench (Sears Craftsman) and I could not tell whether the bolts yielded or not during the initial torque. I think the final torque was by angle and the bolts did not all feel the same, most were smooth and quiet a about 3 of them squeaked. Not sure if the squeaking was an indication if the bolt yielded or not. I did not try to loosen and re-torque the squeaky bolts and left them and it seemed to have been OK.

[TylerDurden]

Yeah the last bit is by angle, but I was watching the beam indicator too.  The ones that did not yield did not allow the angle turn... they were really stubborn and I didn't want to totally reef on em.

[92EcoDiesel Jetta]

Yeah the last bit is by angle, but I was watching the beam indicator too.  The ones that did not yield did not allow the angle turn... they were really stubborn and I didn't want to totally reef on em.

Did you mean on the bolts that did not angle turn, the torque wrench indicated they should have turned. What were the torque values on the ones that angle turned vs the ones that did not angle turn?

[TylerDurden]

The ones that angle turned went to ~85-90, IIRC. The stubborn ones were not budging at >100.

[745 turbogreasel]

I always clean, dry and oil every fastener in an engine unless it specifies not to.
Going over 100lbs on a 12MM head is not abnormal.
If you stopped and chickened out, what are you going to do on the warm retorqes?
IMO, watching the torque is a waste of time, the bolts don't work that way, and if they break like the really cheap ones do, spin out the nub and put in another.
I'd back each  out, lightly oil it on the threads and the washer, tighten it to 35,  move to the next, then start over.

[TylerDurden]

Going over 100lbs on a 12MM head is not abnormal.
IMO, watching the torque is a waste of time, the bolts don't work that way,

Please explain.

[burn_your_money]

Personally I'm surprised that you only hit 85 ft-lbs. I don't use a torque wrench for the angle part of the procedure but by pulling on my 36" breaker bar, I know it's a lot more than 85.

[745 turbogreasel]

Going over 100lbs on a 12MM head is not abnormal. When I started with VW diesels, it seems I really had to reef on em, so i did a few with the clicker, and some were in the upper hundredandteens.
IMO, watching the torque is a waste of time, the bolts don't work that way, They are designed for an angle torque application , because doing it the old way wasn't good/consistent enough.  Therefor watching the  beam wrench does not  deliver useful information.

Please explain.

That answer your question?

[R.O.R-2.0]

Going over 100lbs on a 12MM head is not abnormal. When I started with VW diesels, it seems I really had to reef on em, so i did a few with the clicker, and some were in the upper hundredandteens.
IMO, watching the torque is a waste of time, the bolts don't work that way, They are designed for an angle torque application , because doing it the old way wasn't good/consistent enough.  Therefor watching the  beam wrench does not  deliver useful information.

Please explain.

That answer your question?

120 ft lbs is not unheard of with yielded bolts...

[smutts]

I understand the theory of TTY bolts, but it still scares me to death doing it. On the brighter side, the last blown head gasket on my SB was a bit strange, Bought it for peanuts at 100k miles, ran like a scalded weasel but started to drip water at 170K, leaked for a while before it popped at 180k, weird thing was when dismantling, the head bolt at the blown corner was only finger tight. I've inherited someone elses bodge thinks I. But the gasket was the original Reinz with the same date stamp as when the car was built in 1991. It hasn't lost a drop in the 40k miles since. So did it leave the factory like that? That would be a very stiff head.

Back to the subject, I oil mine, as it depends on the angle the bolt is turned, so whatever makes life easy for those threads.

[TylerDurden]

Thank you for the replies. 

My conclusion:
Bolts must be oiled.
Bentley Publishing has a serious omission by not mentioning this critical factor.


I did a little more reading on the subject. 
This was the most informative:
Engineering Fundamentals of Threaded Fastener Design and Analysis

This is also a short but interesting read, regarding re-using stretch bolts:
Bolt Science: More Thoughts on Fastening


The short story:

Bolt lubrication allows the fastener to transfer more of the turning energy into clamping force and reaching the required plastic range of deformation.
Excessive friction in the threads (due to debris, corrosion, etc.) can also result in torsion strain that releases in heat/cool cycles, reducing clamping force.
Overtightening (a common source of leaks) is not likely, due to the plastic nature of stretch-bolts.

Some nuggets:

The torque applied to a fastener is absorbed in three main areas. First, there is underhead friction, which may absorb 50 percent or more of the total torque. Thread friction absorbs as much as 40 percent of the applied torque. The final 10 percent of the applied torque develops the clamping force that holds the components together. Thus an increase in either friction component of 5% can reduce tension by half.

*****

When torque-only control is used as the method for tightening a fastener, there is absolutely no way to be 100 percent certain that the desired tension will be created. Using installation torque alone to control the process always introduces an element of “statistical gambling” into the assembly process. Installation torque measurements that are not backed up with simultaneous angle-of-turn measurements cannot be totally relied upon to insure that proper fastener installation has been accomplished.

For bolted joints where safety and reliable performance are dependent upon proper initial tension, both torque and angle-of-turn must be monitored and controlled during the tightening process. As each fastener is installed, the torque-angle tightening signature of the bolted joint should be compared to established assembly process limits to insure that the specified assembly preload has been achieved.

The fundamental tightening procedure for Torque-Angle-Tension Control is simply defined as follows.
1. Torque is applied until a specified “threshold” level is attained.
2. An additional angle-of-turn is applied to finish the installation.


*****

The most general model of the fastener tightening process has four distinct zones as illustrated in Figure 19.

Zone 1 is the rundown or prevailing torque zone that occurs before the fastener or nut contacts the bearing surface. Prevailing torque due to thread locking features such as nylon inserts or deformed threads will show up in the rundown zone. Frictional drag on the shank or threads due to misalignment of parts, chips or foreign material in the threads as well as unintended interference due to out of tolerance threads are additional causes of prevailing torque in the rundown zone.

Zone 2, is the alignment or snugging zone, wherein the fastener and joint mating surfaces are drawn into alignment, or a stable, clamped condition. The nonlinear alignment zone is a complex function of the process of drawing together the mating parts, and bending of the fastener as a result of non-parallelism of the bearing surface to the fastener underhead surface. In addition to the macro effects related to alignment of parts, there are micro effects within the alignment zone. The micro effects include contact stress-induced deformations of plating and coatings as well as local surface roughness and thread deformations.

Zone 3, is the elastic clamping zone, wherein the slope of the torque-angle signature curve is constant. The elastic clamping zone torque-angle slope is a very important characteristic of each bolted joint. This slope can be projected backward to locate the elastic origin. Angle-of-turn from the elastic origin is multiplied by the angle-tension coefficient to calculate the tension that has been created by the tightening process.

Zone 4, as shown in Figure 19, is the post-yield zone, which begins with an inflection point at the end of the elastic clamping range. Yielding can occur in the bolt or in the joint assembly, as a result of underhead embedment or as thread strip in the bolt or mating threads. The yield point can be used to establish or verify the tension-angle coefficient for the torque-angle-tension tightening process.


*****

For this process to work reliably, it is necessary that the threshold torque level for starting angle counting be set at a level which is above the alignment zone of the tightening process.

The range of final torque values on the engine I'm working on ranged from 108ft-lb to 140ft-lb.

Following the Bentley sequence, torque values at the end of angle-tightening (in ft-lbs):

Bolt #	1	2	3	4	5	6	7	8	9	10
First 1/4 turn:	90	115	90	95	90	85	100	80	115	100
Second 1/4 turn:	108	115	100	115	120	120	120	100	140	110

I don't think using a bolt with relief cuts is adequate to chase threads, the ones I tried were too loose to address corrosion. A tap would be better, methinks.

[JFettig]

NO, you do NOT oil stock head bolts!

There is a reason you angle tighten them and not torque them to a certain number. Torquing them to only 44ft-lbs then angle tightening eliminates most of the friction error. DO NOT OIL

If you oil head bolts you'll only get about 80-110ft-lbs out of them, if you try for more you'll just stretch the hell out of them... My haynes manual says to oil them, Bentley says DRY! Bentley is correct.

I am experimenting with something new, I use 12.9 SHCS, M12x1.75 by 110mm long, 115-125ft-lbs OILED(30w oil).  pick your torque and use the same torque for all of them. Make sure to clean the holes out very well, sucking out any fluid that is in them to prevent cracking the block.

http://www.mcmaster.com/nav/enter.asp?partnum=91290A642
http://www.mcmaster.com/#98035A107