Misprint in Factory TTY Head Bolt Procedure?

[DMan]

Hello,

I have an 86 Buick Regal GM manual that I bought 10 years ago. It says that the procedure to tighten factory TTY head bolts is to tighten to 25 ft lbs, then go 1/4 turn and again 1/4 turn BUT if you hit 60 ft-lbs at anypoint during the 1/4 turns, stop.

Is this correct? I thought the procedure was to go to 25 ft lbs, then 1/4 and 1/4, with no regard to what the torque reading was. Can someone confirm or deny this?

Regards,

 

[Nick Micale]

That is correct for the V-6 Buick.

Is it correct for a turbo V-6 Buick?

Just like the bearing clearances specified in the manual, probably does NOT apply to the turbo motors.

 

[sumnerw]

Nick -

Do you know what the proper TTY torquing procedure is for the LC2? I, for one, have had very poor results with the procedure listed in the manual (stop at 60 ft-lbs).

Thanks,
Buzz White in Houston, TX (sumnerw@flash.net)

 

[DMan]

Can anyone say for certain what the tty procedure is?

ttt

 

[inkcushion]

I just torqed mine to 62lbs right off and I haven't had a problem since. just my 2 cents......................Alan

 

[Jeff Harrington]

torque all bolts to 25#, then with an angle meter driven by your torque wrench set at 60# turn it to 90 degrees on all bolts, then start the torque sequence again with another 90 degrees or when your torque wrench clicks.

 

[DMan]

So for all intents and purposes, stock head bolts are torqued to 60 ft lbs?

 

[tminer]

Torque to 60 lbs in 90* increments starting at 25 lbs.

The difference is specifying an angular increment instead of a torque increment (like 25-35-45-55-60 or something). The angular increment is more accurate. Kind of like measuring bolt stretch is more accurate for tightening rod bolts.

Of course the accuracy of the 25 and 60 lb end points is still a problem, but the angular method will still help to in torqueing them down evenly. It might help to torque them down to 25 and release them a few times, but I don't know for sure if that would be a problem with the TTY style bolts. I wouldn't think so, but???

HTH,
Tom

 

[turbodave231]

I can speak with 100% certainty and say that the factory procedure you quoted it correct and it applies to the turbo LC2 engine (and all other V6 engines for 1986-1987).

Effectively you stop at 60 lbs/ft of torque because you always hit the max torque before you complete the 90 degrees.

Follow the procedure if you are using GM head bolts. It works.

DR

 

[DMan]

Coming back to this thread a few months later, I think there is some confusion here.

I think the factory manual has a misprint.

If you are using TTY bolts (NOT ARPS), and you follow the stated procedure of starting at 25 ft lbs, then go 1/4 Turn and another 1/4 Turn, you hit the 60 ft lb threshold before you're done the first 1/4 turn. Whats the point of the second attempt at a 1/4 turn if you're already at the stated 60 ft-lb limit?

Also, why would ARP bolts be torqued to 75-85 ft lbs (generally accepted ARP torque range), and the factory bolts 60? More contradiction.

So I asked my mechanic, he checked his books, and this procedure is the same for regular v6 engines. That doesnt make sense either, because this turbo motor sees alot more cylinder pressure than a NA v6 - unless the NA v6 torque specs where HIGHLY overrated, which I doubt.

As Tom correctly stated earlier, the 1/4-turn 1/4-turn angle based methodology is more accurate than specifying a target torque level because it creates a known bolt stretch. A torque spec can be affected by friction (crud on the threads, poor lubrication of threads) and so on..

So what did I finally do? Used factory TTY bolts, torqued to 25 ft-lbs, and went an additional 1/4 turn & 1/4 turn, without regard to the 60 ft-lb limit. Result - torque wrench read between 90-100 ft lbs depending on the bolt. I think this is the correct procedure.

Any comments?

 

[Ormand]

The stock bolts are TTY. That is torque to YIELD. The bolts take a permanent set when they are fully torqued, which is why you can't reuse them. They MAY do the 90 degrees without getting to 60 ft-lbs, in which case you stop at lower than 60 ft-lbs. The ARP bolts have a higher torque value because they are much stronger material, and won't yield at a wimpy 60 ft-lbs. Don't know why Buick used the TTY bolts, maybe some assembly line idea, or maybe cost, or maybe to serve as "weak link" so that head gaskets blow before something more expensive to fix.

 

[DMan]

Originally posted by Ormand
The stock bolts are TTY. That is torque to YIELD. The bolts take a permanent set when they are fully torqued, which is why you can't reuse them. They MAY do the 90 degrees without getting to 60 ft-lbs, in which case you stop at lower than 60 ft-lbs. The ARP bolts have a higher torque value because they are much stronger material, and won't yield at a wimpy 60 ft-lbs. Don't know why Buick used the TTY bolts, maybe some assembly line idea, or maybe cost, or maybe to serve as "weak link" so that head gaskets blow before something more expensive to fix.

I agree with your description of TTY, but what you are implying does not jive with the concept of TTY (in my opinion).

Here is what I believe - On a cylinder head, you want a nice, even pressure applied around the perimeter. TTY is a good way to achieve that because by turning a bolt a known rotation on a thread that has a known pitch, I can now calculate how much I am stretching the bolt, and I can subsequently find the stress on the bolt by looking at a stress-strain curve for the given bolt material. I can then compute clamping force. For TTY, it means that I will go beyond the elastic limit of the material and the bolt is junk after one use.

If I don't turn all the bolts the same amount, because I have reached the '60 ft-lb limit' then the clamping force on each bolt will be different. I'm not sure, but I'm willing to bet that 60 ft-lbs is not enough to yield these bolts.

Would probably need to talk to some experienced engineers to know why TTY is used. But I like the theory that it makes better sense to let a head gasket blow than breaking something.

 

[Rickracer]

The theory behind TTY bolts relies on very consistent quality

Do we get consistent quality from the vendors that supply GM with head bolts basically at the lowest bid? That is a question that either takes an engineer to determine, or you have to decide for yourselves. They are designed to be basically idiot proof. TTYs makes a good attemp at achieving repeatable results motor after motor on the assembly line, based on a set of parameters specified by engineers whose job is to design a product that will have few if any warranty problems, and be suitable for the "majority" of their purchasers. Do we , as a group, fall into this category? What we wind up with is a set of compromises based on the bottom line, both before and after the sale. On the other hand, you have manufacturers like ARP, who design and build products that have a singular purpose in mind, which is to be the best bolts made, period, and to hold pressures that would scare the crap out of the engineers that designed the thing to begin with. When properly prepped and installed,they will achieve far better sealing than TTY bolts, in my opinion. Personally, I'd choose the special bolts, cuz I've got a special purpose for them.

 

[325DR]

Originally posted by DMan
If you are using TTY bolts (NOT ARPS), and you follow the stated procedure of starting at 25 ft lbs, then go 1/4 Turn and another 1/4 Turn, you hit the 60 ft lb threshold before you're done the first 1/4 turn. Whats the point of the second attempt at a 1/4 turn if you're already at the stated 60 ft-lb limit?

If you were to tighten just ONE bolt to 60 ft-lbs, and then put in the other 7 bolts and tighten them to 60 ft-lbs, the first bolt will not still be at 60 ft-lbs since the majority of the clamping force on the head is taken care of by the other 7 bolts. Doulbe check all head bolts when you are all done after you have gone through the process of going an additional 90 degrees to get to your 60 ft-lb mark.

 

[DMan]

325DR,

I thought that was case as well, but its not. After I hit 60 ft-lbs during the first 1/4 turn, I was done. I hit 60 ft lbs about 60-70 degrees into the first 1/4 turn. Even after I came back to the first bolt after tightening the other seven, it was still at 60.

Still think there is a misprint. I can't think of, or be convinced (yet) that there is any reason for the 60 ft lb limit.

Good discussion though! Would like to flush this out.

 

[tom h]

Some possibly helpful background information on TTY bolts and the principle, down below. I believe the idea behind an initial 25 ft-lb torque, is that at low torque values the effect of thread and under-head friction, and the phenomena of "stiction" , are much less pronounced. ie, a low torque (25 ft-lbs) is more likely to be accurate than a high value (60-70 ft-lbs), so they use 25 ft-lbs as a reasonably repeatable starting point.

In situations where you can caliper measure between the bolt head and its opposite end, the total bolt elongation (as an indicator of the bolt's clamping force) is perhaps the most accurate method to judge the "true" clamping force a bolt exerts.

The part of GM's instructions that DOESN'T make sense, is stopping at 60 ft-lbs, given the vagaries of torque, friction, and stiction. I would have thought the right way is is do the stated quarter-turns no matter what, but I would be hesitant to second guess...

http://www.oliver-rods.com/library/libraryindex.html

Q: Why can't your bolts be torqued?

A: Any bolt can be torqued. The question is: will using the torque method of tightening a bolt give you good, repeatable results? This is important because at top dead center of the exhaust stroke, the piston wants to continue right up through the cylinder head and the crankshaft wants to pull the piston back down the cylinder walls. At high RPM this load can exceed 18,000 pounds of pull on the cap. It is the job of the bolt(s) to provide enough clamping force to keep the cap from separating from the tower of the rod. The problem is a torque wrench only measures friction not clamp load and every time you tighten the bolts you change the mating surfaces of the threads and where the head of the bolt contacts the rod. This changes the amount of friction that must be overcome to correctly tighten the bolt. What this means is if you tighten the bolts to the same torque level, you will have a different clamp load on the bolts each time. Because of the large potential variations in the actual clamp loads achieved by using torque, we strongly recommend against using torque.



Q: Why use torque and angle?

A: We didn't invent this. It has been used by automobile and diesel manufacturers and in the aerospace industry for many years because it is much more accurate than using torque to tighten bolts. Torque and Angle uses the pitch of the threads as a good, repeatable reference for properly tightening the bolts. For example, if the bolt has a 7/16" 20 threads per inch pitch, then one full (360 degree) turn of the bolt will move the bolt exactly .050" (fifty thousandths of an inch), or 36 degrees of turn will move the bolt exactly .005" (5 thousandths of an inch). We have a specification for Torque and Angle for all of our bolts, no matter their size (5/16", 3/8", 7/16" etc.) and our specs are all derived from the pitch of the specific thread on each size of bolt.

 

[Rickracer]

I definitely agree with torque angle method being superior

It's the closest way of determining bolt stretch, which is what we're really after. Bolt stretch is definitely the best method, if possible. But we're still stuck with starting from a torque reading initially, on most applications. TTY stopping at a preset torque doesn't go the whole route though, and isn't the same as torque angle.