Re: GM 3.4L V-6 with cast iron block and aluminum heads; new Fel-Pro PermaTorque head gasket & new Fel-Pro head bolts.
I had failed head gaskets on both heads of a 1998 Chevy Venture ( #1 & #2 cylinders). Upon installing the back head (the worst one to access) I torqued all 8 bolts to the updated 44 lb-ft and the 95 degree torque angle with the new torque sequence. I believed that I did it correctly but then after lunch just for "fun" I went back over the head bolts with my beam-style torque wrench to confirm that all the bolts didn't turn before the 44 lb-ft. One bolt (lower passenger-side corner of back head; coincidentally the end where the old gasket had failed. This bolt threads into the alignment dowel) turned before the beam torque wrench even got to the 44 lb-ft. I swear I torqued it properly in sequence and although it was a PITA to do, I felt that I also did the 95degrees pretty accurately on this bolt.
Question 1) So why would this one bolt turn at less than the initial torque? Has anyone had this problem before? I understand that these bolts undergo plastic deformation during the 95degree final torque, so given that, I am reluctant to re-tighten this one bolt to the 44 lb-ft and re-do the
95 degrees possibly stripping the bolt or block threads (alignment dowel threads). I am reluctant to buy a new set of bolts and redo the whole head and gasket especially because I believe I did it "by the book" this first time. Perhaps I could just tighten it to 65-75?? lb-ft (the old torque specs on this engines "pre-torque angle" predecessor) or . . . .
Question 2) The bigger question is HOW TO CONFIRM that torque-to-yield bolts are "tight enough"? In the old days of plain torque one could go back over the bolts and make sure they don't turn below the spec torque. But with torque angle--how does one check tightness?
Question 3) I am sure some engineer's handbook somewhere has torque (lb-ft or Nm) to torque angle "conversion" for these bolts with chased, clean, oiled threads, so where is it posted on the internet?
I had failed head gaskets on both heads of a 1998 Chevy Venture ( #1 & #2 cylinders). Upon installing the back head (the worst one to access) I torqued all 8 bolts to the updated 44 lb-ft and the 95 degree torque angle with the new torque sequence. I believed that I did it correctly but then after lunch just for "fun" I went back over the head bolts with my beam-style torque wrench to confirm that all the bolts didn't turn before the 44 lb-ft. One bolt (lower passenger-side corner of back head; coincidentally the end where the old gasket had failed. This bolt threads into the alignment dowel) turned before the beam torque wrench even got to the 44 lb-ft. I swear I torqued it properly in sequence and although it was a PITA to do, I felt that I also did the 95degrees pretty accurately on this bolt.
Question 1) So why would this one bolt turn at less than the initial torque? Has anyone had this problem before? I understand that these bolts undergo plastic deformation during the 95degree final torque, so given that, I am reluctant to re-tighten this one bolt to the 44 lb-ft and re-do the
95 degrees possibly stripping the bolt or block threads (alignment dowel threads). I am reluctant to buy a new set of bolts and redo the whole head and gasket especially because I believe I did it "by the book" this first time. Perhaps I could just tighten it to 65-75?? lb-ft (the old torque specs on this engines "pre-torque angle" predecessor) or . . . .
Question 2) The bigger question is HOW TO CONFIRM that torque-to-yield bolts are "tight enough"? In the old days of plain torque one could go back over the bolts and make sure they don't turn below the spec torque. But with torque angle--how does one check tightness?
Question 3) I am sure some engineer's handbook somewhere has torque (lb-ft or Nm) to torque angle "conversion" for these bolts with chased, clean, oiled threads, so where is it posted on the internet?