Pulled heads off my vue.
Has torque to yield bolts.
Got new bolts.
They are exactly the same length as old bolts.
Within .001-002"
How come? Or is the stretch on old bolts just hard to measure?
TTY bolts can only be used once because they stretch to apply the proper clamping force.
If reused, they will continue to stretch without applying the proper clamping force.
https://en.wikipedia.org/wiki/Torque-to-yield_fastene
Tester
i have an evil, unloved saturn so its hard to find info. the sohc torquing procedure is different than the dohc motors. my motor is the maligned opel 3.0 which is used in saabs. not SOB but close. it says to torque the bolts to 30lbs and let them sit and than take them out and oil them and put them back and torque to 30lbs than 44lbs than a final 90deg turn. my torque values are an example and only to illustrate the unique torquing procedure. put them in, take them out, torque to fl/lbs than torque angle. and you wonder why i have been looking at this vue in garage for 3 months.
You better get the torque right!
Because if you don’t, the heads will have to come off to replace the head gaskets, and new TTY bolts will have to be purchased.
You can pretty much eye-ball a 90 degree final torque angle.
But some head bolts require a 110 degree final torque angle.
And in those cases, you need a torque angle gauge.
Tester
Found some info
Initial torque is 18ft/lbs
90deg next pass
90deg next pass
90 deg next pass
15deg final pass
I’ve seen torque procedures like that on tty bolts for other cars. I expect that procedure isn’t overly unusual.
main question was bolt stretch. As in, do they stretch? Read a bit on Saturn site about some guy who reused old 4cyl sohc bolts and he said the old bolts stretched about 1/4". Which sounds like bull. But than, I have no way of knowing exactly how long my bolts were at factory. Yes the aftermarket bolts are very close to them in length. But they are 2 different sets.
You also have to torque the bolts in a specific pattern.
sequence also. yep.
so, if you torque to 18 lbs to start and than do 90 degs that is a certain amount of extra torque. say 90 deg=23 additional ft/lbs. and than you do another pass at 90 deg. will that also be 23 lbs? and so on? i was just wondering. does each additional 90 deg pass have the same affect? since there are 3 90 deg passes in total.
Note the bolts are torque TO yield not torqued PAST yield. Past yield would permanently stretch the bolt. Up TO yield will spring back to the original length. If you add load to any bolt it stretches. How much it stretches depends on home much load you apply. The best use of the bolt is to tighten it as close to yield as you can without going over. Replacing TTY bolts insures that IF you went over, the bolts get replaced as a precaution.
Let’s use a torqued to stretch rod bolt as an example. Take a look at the article;
http://www.performanceenginetech.com/connecting-rod-bolts-stretch-vs-torque/
Note that torquing to a stretch value of 75% of yield is only about 5 thousandths of an inch where yield is at 7 thou. Since you can’t measure the length of a head bolt while you tighten it, the angle measurements define how much stretch the bolts gets since the thread pitch is consistent and repeatable.
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No, the additional 90 degree will not show 23 ft-lbs. Why? because the friction on the thread goes up with more load and that causes a higher torque value. But that doesn’t matter since you are twisting to an angle rather than a torque.
dad has ratchet adapter. Don’t use it much.
Use a breaker bar!
Zero the torque angle gauge, and then torque the bolts 90 degrees with the breaker bar.
Not rocket science.
Tester
I want to use the ratchet adapter with the breaker bar. You know getting in the proper position with a breaker bar bites. You pull the bar 20-30 degrees and than have to shift position to finish the 90 deg pass. The motor is not on an engine stand.
Any mechanic worth their salt, knows where to position themselves when it comes to the final torque angle spec.
Tester