I think I should have posted this in this forum instead of the cabriolet forum. I was wondering if anyone experienced the same issues of the head bolts "yielding" or "letting go" during the 90 degree additional turn after the 43 ft/ lb./ torque. They did not strip but they lost some torque as I suspect they started to stretch. Here is my question with more information in the Cabriolet forum.
Sounds intuitive that they are supposed to stretch...I know, but I've never worked with them before and it just felt weird when they started to stretch. I was looking for people who had experience with them and not just opinions. Some with experience said they never felt them stretch, which got me thinking that I somehow messed up or got a bad set of bolts, or something was messed up with my case. Thanks
Last edited by 84Westfalia; 08-16-2012 at 04:25 PM.
It is important to understand this is a precision process.
My limited experience with the TTY (Torque-To-Yield) headbolts is that I feel the my applied torque level out at the very end of the final turn sequence.
The feeling you have is that the bolt is getting ready to snap, so that makes you uneasy, since it goes against your instinct. However, this is normal behavior for a stretch bolt.
How do you make sure you will get to the bolts to this point, not before and not beyond where they begin to weaken?
First, the headbolt holes need to be chased with a thread restorer. That is ideal. It you don't have a thread restorer, then you can use a bottoming tap. If you don't have a bottoming tap, then take a regular tap and cut off the tapered end with a silicon carbide cutting wheel on a dremel tool.
Clean the debris from the holes with compressed air.
If you do not chase the bolt holes, friction will cause the bolts to be under-torqued, and since the stretch part is at the very end of the sequence (I want to say about the last 10 degrees), you may not even get to the stretch phase.
Normally, the headbolts are lightly pre-oiled. Do NOT use anything else on the bolts or holes. The sequence is calibrated for the lubricant on the bolts. If the bolts are bone dry, use a light-grade machine oil, certainly no anti-seize.
Your torque wrench must be checked for calibration. You might be able to find a tool dealer or shop that has a tester. Learn how to use your torque wrench properly and don't loan it to anyone. Back off the setting collar to the lower end of the scale before putting it into storage.
Use a long-handled breaker bar for the final degree turns. You need that leverage to help with the control and to keep your rotator cuff from being pulled. 2 feet would be a good length.
The advantage of the TTY bolt is even clamping pressure which cannot be obtained with non-stretch bolts.
The only bolt better than a TTY is a stud. It is stronger, has even clamping pressure, and is reuseable. TTY bolts are one-use only. The disadvantage is the extra cost over TTY bolts.
Last edited by chickenfriend; 08-17-2012 at 10:52 PM.
Although it is not stated in any repair manual that I can remember, except for the diesel engine which uses a larger bolt and the same torque data, they should not be reused. Maybe one time is OK if they feel right when using it, but even one time I think is pushing your luck.