Fox T-Bird/Cougar Forums  

@JeremiB 
Exactly what you said is what i understand is FACT. But check this out. Here is another wrench in the works!!! Studs for example naturally have the pitch and size of the engine they are designed for. But the nut side is normally a fine thread. This makes the clamping load more consistent. So normally they reduce the torque specks on that type of arrangement. You know something we remove and install  bolts and dont really know much about there design and function. I remove Bolts every day from brake calipers to head bolts. But do we really think about them other than what size socket we need to remove them or tighten them up???? Silly but true!! Thanks great discussion!!

Why are these 70-100ft/lb bolts so sensitive in the first place? With thick enough surfaces, it shouldn't matter at all if it's +/- 10ft/lbs. I don't think the bolts on our heavy, thick-enough fox body motors are too sensitive to the torque values compared to newer vehicles. Get it in the general vicinity and they last beyond the point where freshening up is needed. Is it due to thinner castings and aluminum being used instead of iron? That should be much more sensitive to torque values.

Pieces clamping down bearings I can see being a little more sensitive to torque. I just don't understand TTY for heads, especially when it appears to do nothing for extending the life of head gaskets or head straightness when poor choices were made elsewhere by the engineers (Subaru notably).

I don't even believe specific torque values are needed to be exact. I've always assumed that the torque was more to make sure all the bolts were the same so you do not hurt the housings or strip out threads.

Head bolt torquing involved considerable development, the difficulty being the differential expansion of the aluminum heads and steel bolts, augmented by different clamping loads resulting from two bolt lengths. Variations in bolt thread friction and bolt head to cylinder head contact friction, due to small  part-to-part manufacturing variations, resulted in significant axial bolt load variation for a specific applied bolt torque. The objective was to tighten the bolts with automatic torquing machines to provide an axial load of 10,000 to 12,000 lbs. without initiating yield, which occurs at approximately 13,500 lbs. with the 11 mm bolts used. It had been assumed that steel washers would be required to protect the aluminum head from being scored by the bolt during torquing, however, this added interface contributed to the friction variation. A "UBS" bolt, with a washer-like surface formed into the head, was evaluated and did not mar the head surface even after repeated retorquing. The automatic torquing sequence that was developed consists of:

• Install UBS head bolts and torque to 72 to 87 Nm to equalize the thread friction and set the gasket.
• Back the bolts out 2 turns.
• Retorque the bolts to 72 to 87 Nm.

The production automatic torquing machines have torque sensors and recorders. If a bolt is not torque within the specified range the operator is signaled and the suspect bolt is replaced. If a problem is encountered during hot test, or quality control durability testing, the torque applied to each head bolt on that engine can be obtained from the records. A mattress type head gasket with a solid steel core and stainless steel fire ring was developed to match the requirements of the less rigid aluminum head with its differential bolt expansion.

I remember that procedure as i was doing a tun of those head gaskets. But Fel Pro said it was not necessary with there gaskets. The perma torque gaskets did not take a set. Now back to studs. The Midnighter is fitted with studs as well as my TYPHOON. I am coming to the conclusion that studs are a waste of time. As TTY bolts are the best thing at this point. But ARP tells a different story. They claim there studs are better by a long run. So once again i am getting a HEADACHE!!!

I question how we've managed to have combustion engines for over a century. Again, I don't see the point. I only come back to the manufacturer saving money somewhere, and that's why the change. I don't think there are too many engines failing on cars, under warranty, that are due to fasteners not being TTY or too much inconsistency across bolts.

Until recently, internal combustion engines didn't care about weight savings, CAFE, use aluminum heads with iron block, etc. All these advances require more forethought for bolted joints. Reducing casting thickness and number of fasteners could very well require TTYs in order to meet reliability requirements.
The Ford case very well could be "saving money" since they added TTY somewhat late in the design process. (The head bolts weren't TTY in the 1982 paper). Maybe they needed the ~20% more clamping force a TTY gets for the same size. An upsize of the head bolt would require re-qualification at a minimum, block/head redesign at worst.

I guess we'll agree to disagree.

I was in a training course with a Dodge engineer whose job it was to minimize the length of A/C hoses to decrease weight. Etc, Etc.

I've got some aquantances I know from Honda R&D I'll see this summer. Will ask them how they are directed design-wise - performance, weight, cost.