Goto the gnttype.org archives and do a search for Robert Caruth, he had direct involvement with the Buick v6's. There is a lot of valuable info from him.
Here is one response from him on head bolts (I hope no one minds):
"Hi all
This one is in my ball park (Head bolts)so here goes.
Torque to yield means there is permanent elongation of the bolt. As an example, if you measure bolt lengths before installation, torque them to spec. remove them and measure again,and if the bolt has yielded it will be longer. A TTY spec. usually says .002 to .012 in. permanent elongation. Thus the material has been yielded. As long as it has been yielded ,the clamp load is determined by the strength of the bolt material not by the torque on it. (Standard specs. stretch the bolts but they will return to their original length when loosened.) This method (tty)has the least amount of variation of any other fastening processes. We center bolts (put a dimple in the ends) measure them with ball
micrometers then torque up these bolts and remove them again to remeasure. 1 engine per day , per engine series to verify our equipment is doing it’s job.(Also monitor torque and angle on every engine built) We use computer controlled DC electric fastening equipment.
Tty is not a process easily duplicated in your garage. That is why so many people switch bolts and use straight torque. Unfortunately just torque has the most variation and as a result you get the most uneven clampload of any fastening processes. Our spec now ( on Series II) is torque + angle into yield which is easier to approximate with hand tools. If any one is interested I can provide the details. I believe the last update of the “G” body service manual calls out a torque + angle + angle.( 25ftlbs. + 90 degrees + 90 degrees (of rotation)) done sequentially.
TTY bolts have a large material safety factor built into them, they do get reused on standard rebuilds, BUT this is not a reuse over and over forever type thing. If you don’t know the history of your engine or change head gaskets frequently the ONLY safe thing to do is Change bolts. Whether GM or aftermarket is a matter of preference I guess. IMOP if people better understood TTY, clampload and fastening in general they could get satisfactory results from tty bolts. All Buick V-6’s have had TTY head bolts from the factory since the early 1980’s.
Hope this has made TTY clear as mud for every one.
Sorry about all the BW
Robert Caruth GMPT Flint V-6"
Last set I put into place cost less than $40.00 to do both sides from NAPA.
