How Critical is 180* when installing head bolts?
12-24-2010, 09:25 AM
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How Critical is 180* when installing head bolts?
I installed new head gaskets on my '92 4Runner 3VZE 3.0L yesterday with new head bolts. The 4runner had blown a head gasket so I had the heads milled, etc. I'm starting to second guess my "accuracy" with the two passes of 90* that I did, so I was hoping to get some other opinions. Basically, what I did was start with the breaker bar 90* to the head and torque it so that the wrench was parallel to the head. I did not mark the heads of the bolts as the FSM suggests... I usually am much more thorough than this, I am kinda confused as to why I rushed this 
. Anyway, I'm just wondering if all the head bolts are within a 1/8 turn of eachother, will that be sufficient? Thanks in advance...
. Anyway, I'm just wondering if all the head bolts are within a 1/8 turn of eachother, will that be sufficient? Thanks in advance...
Last edited by mattster03; 12-24-2010 at 09:26 AM.
12-24-2010, 04:17 PM
#4
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I also think youll be ok. Just make sure the cooling system is up to spec to keep that HG good. Also, might want to consider getting some headder wrap to go around the crosover pipe before it goes back in.
12-24-2010, 06:29 PM
#5
I'm not able to follow that line of reasoning. You're not releasing torque by stopping the turning of the fastener. The only way to release torque is to turn the fastener in the opposite direction.
Anywho, the FSM says to torque to yield the head bolts in 2 seperate 90° increments after the intial torque of 33ft.lbs. is achieved. I believe their point in stating to do so was in an effort to apply tension to the head more evenly, as to prevent any possible distortion of it during the process.
http://personal.utulsa.edu/~nathan-b...68cylinder.pdf
To the OP, I don't know. Maybe something bad, maybe something good? But of all the torque specs on the entire engine, those would arguably be the most important ones to get right. Who knows though, maybe you did?
Anywho, the FSM says to torque to yield the head bolts in 2 seperate 90° increments after the intial torque of 33ft.lbs. is achieved. I believe their point in stating to do so was in an effort to apply tension to the head more evenly, as to prevent any possible distortion of it during the process.
B. Install cylinder head (12 pointed head) bolts
HINT:
• The cylinder head bolts are tightened in three
progressive steps (steps (c), (e) and (f)).
• If any bolts is broken or deformed, replace it.
(a) Apply a light coat of engine oil on the threads and
under the heads of the cylinder head bolts.
(b) Install the plate washer to the cylinder head bolt.
(c) Install and uniformly tighten the eight cylinder head
bolts on one side of the cylinder head in several
passes, in the sequence shown, then do the other side
as shown.
Torque: 44 N–m (450 kgf–cm, 33 ft–Ibf)
If any one of the bolts does not meet the torque
specification, replace the bolt.
(d) Mark the front of the cylinder head bolt head with
paint.
(f) Retighten cylinder head bolts by an additional 90°.
(g) Check that the painted mark is now facing rearward.
(e) Retighten the cylinder head bolts 90° in the numerical
order shown.
HINT:
• The cylinder head bolts are tightened in three
progressive steps (steps (c), (e) and (f)).
• If any bolts is broken or deformed, replace it.
(a) Apply a light coat of engine oil on the threads and
under the heads of the cylinder head bolts.
(b) Install the plate washer to the cylinder head bolt.
(c) Install and uniformly tighten the eight cylinder head
bolts on one side of the cylinder head in several
passes, in the sequence shown, then do the other side
as shown.
Torque: 44 N–m (450 kgf–cm, 33 ft–Ibf)
If any one of the bolts does not meet the torque
specification, replace the bolt.
(d) Mark the front of the cylinder head bolt head with
paint.
(f) Retighten cylinder head bolts by an additional 90°.
(g) Check that the painted mark is now facing rearward.
(e) Retighten the cylinder head bolts 90° in the numerical
order shown.
To the OP, I don't know. Maybe something bad, maybe something good? But of all the torque specs on the entire engine, those would arguably be the most important ones to get right. Who knows though, maybe you did?
Last edited by MudHippy; 12-25-2010 at 02:15 PM.
12-25-2010, 02:12 PM
#6
As much as I want to debate that with you, I'll refrain from doing so at this point. I've done some research since we left off, and haven't found anything referencing the specific physical processes by which a fastener could, somehow, lose clamping force in that manner. And, I'm highly doubtful such processes can even occur. However, I'll give you the benefit of the doubt for the time being. Why? I know, it's very uncharacteristic of me to shy away from any argument(especially one that I don't feel I've decisively won). But, something more significant has come to my attention that needs to be addressed first.
So...
I've had a sneaking suspicion that the term TTY(Torque To Yield) has been misused when refering to the head bolts for this engine. It's never made much sense to me why Toyota would recommend reusing head bolts that have been torqued to their yielding point. Wouldn't that be asking for failure of said bolts? As it turns out(pardon the pun)it indeed would be. True TTY fasteners SHOULD NOT be reused under ANY circumstances. So what kind of bolts are these then? Are they formed of a certain material as to allow for some kind of super elasticity? How are they able to be tightened to their yielding point repeatedly without failing? Or is the secret in the tightening procedure itself?
Answer:
The bolts themselves aren't special in their construction. It IS all about the tightening procedure. Which IS NOT really a TTY process afterall. It's actually a process called TTT, Torque Turn to Tighten. In this procedure the bolts are not necessarily torqued to their yielding point. But instead can be tightened to near that "threshold of yield". Which is the point of tension beyond which they lose their ability to "spring back" to their original length when the tension is relieved. That means, theoretically, they CAN safely be reused if they've not been over-tightened/stretched beyond that "threshold" and into their yield zone.
There's several other good reasons, aside from potentially being able to reuse the fasteners, why TTT is a better final torquing procedure when compared to the TTY process. Those are reducing the possibility fastener failure during the tightening process, eliminating frictional variances that might effect the final clamping load achieved, and the resulting minimization of load scatter. Load scatter being the slight differences in final clamping force achieved between the multiple fasteners used to hold one particular part in place. Meaning seperate final clamping loads for each of the bolts holding the heads down, in this instance. That, for obvious reasons, is an undesireable effect.
http://www.enginebuildermag.com/Arti...uetoangle.aspx
So, what are we to glean from all this? The TTT procedure, recommended by Toyota, for tightening the 3VZE head bolts has been carefully engineered to produce the most accurate final torque/clamping load. And, when followed as prescribed, does allow for the reuse of the head bolts. Which, under ordinary circumstances, have not been torqued to their threshold of yield(or beyond).
Most importantly though, THESE ARE NOT TTY HEAD BOLTS!!!
INTERNET MYTH BUSTED!!!
So...
I've had a sneaking suspicion that the term TTY(Torque To Yield) has been misused when refering to the head bolts for this engine. It's never made much sense to me why Toyota would recommend reusing head bolts that have been torqued to their yielding point. Wouldn't that be asking for failure of said bolts? As it turns out(pardon the pun)it indeed would be. True TTY fasteners SHOULD NOT be reused under ANY circumstances. So what kind of bolts are these then? Are they formed of a certain material as to allow for some kind of super elasticity? How are they able to be tightened to their yielding point repeatedly without failing? Or is the secret in the tightening procedure itself?
Answer:
The bolts themselves aren't special in their construction. It IS all about the tightening procedure. Which IS NOT really a TTY process afterall. It's actually a process called TTT, Torque Turn to Tighten. In this procedure the bolts are not necessarily torqued to their yielding point. But instead can be tightened to near that "threshold of yield". Which is the point of tension beyond which they lose their ability to "spring back" to their original length when the tension is relieved. That means, theoretically, they CAN safely be reused if they've not been over-tightened/stretched beyond that "threshold" and into their yield zone.
There's several other good reasons, aside from potentially being able to reuse the fasteners, why TTT is a better final torquing procedure when compared to the TTY process. Those are reducing the possibility fastener failure during the tightening process, eliminating frictional variances that might effect the final clamping load achieved, and the resulting minimization of load scatter. Load scatter being the slight differences in final clamping force achieved between the multiple fasteners used to hold one particular part in place. Meaning seperate final clamping loads for each of the bolts holding the heads down, in this instance. That, for obvious reasons, is an undesireable effect.
Torque Turn to Tighten
One thing that should be obvious by now is that if we’re going to tighten fasteners to the threshold of yield, we need a better method than measuring resistance to turn. Friction variances could easily get us into trouble.
Fortunately there is a method of tightening a fastener that is much more accurate than measuring resistance to turn. It’s called Torque Turn to Tighten (TTT), often referred to as angle turn. With this method, you use a relative low torque to run down and align the fastener, then rely solely on a measured turn to tighten the fastener to the desired level. What we’ve done has not affected the friction in our fastener, it has taken it out of the equation when it comes to tightening.
For instance, 90 degrees of turn is 90 degrees of turn; old bolt, new bolt, rough threads, new threads, it doesn’t matter. The amount of stretch will be extremely uniform from bolt-to-bolt across the joint. Load scatter is kept to a minimum.
TTT is a far superior method of tightening critical fasteners regardless of whether you tighten them to yield or not. Fastener engineers use sophisticated mathematical models to calculate the amount of turn needed to get a desired load, but what has really fueled the rapid growth in this area is sophisticated electronic equipment. Sensitive electronic load sensing cells coupled with angle encoders using advanced software programs have allowed engineers to test their theories watching run down curves in real time as they tighten fasteners.
One thing that should be obvious by now is that if we’re going to tighten fasteners to the threshold of yield, we need a better method than measuring resistance to turn. Friction variances could easily get us into trouble.
Fortunately there is a method of tightening a fastener that is much more accurate than measuring resistance to turn. It’s called Torque Turn to Tighten (TTT), often referred to as angle turn. With this method, you use a relative low torque to run down and align the fastener, then rely solely on a measured turn to tighten the fastener to the desired level. What we’ve done has not affected the friction in our fastener, it has taken it out of the equation when it comes to tightening.
For instance, 90 degrees of turn is 90 degrees of turn; old bolt, new bolt, rough threads, new threads, it doesn’t matter. The amount of stretch will be extremely uniform from bolt-to-bolt across the joint. Load scatter is kept to a minimum.
TTT is a far superior method of tightening critical fasteners regardless of whether you tighten them to yield or not. Fastener engineers use sophisticated mathematical models to calculate the amount of turn needed to get a desired load, but what has really fueled the rapid growth in this area is sophisticated electronic equipment. Sensitive electronic load sensing cells coupled with angle encoders using advanced software programs have allowed engineers to test their theories watching run down curves in real time as they tighten fasteners.
So, what are we to glean from all this? The TTT procedure, recommended by Toyota, for tightening the 3VZE head bolts has been carefully engineered to produce the most accurate final torque/clamping load. And, when followed as prescribed, does allow for the reuse of the head bolts. Which, under ordinary circumstances, have not been torqued to their threshold of yield(or beyond).
Most importantly though, THESE ARE NOT TTY HEAD BOLTS!!!
INTERNET MYTH BUSTED!!!
Last edited by MudHippy; 12-25-2010 at 02:21 PM.
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