25-06-2023, 05:53 AM
As part of my engine recondition, I decided to save money by reusing the old head studs. To my regret, I used a recently purchased die nut to clean up the threads on the upper end of the studs. The die nut was very tight on the threads and took off a significant amount of metal. After doing a few studs, I tried the nuts on the studs and found that they were very loose, and didn't use the die nut on the remaining studs.
When tightening the nuts with the head in place, one of the loose nuts sheared it's thread at a torque of 10 lb-ft. Trying a second nut on that stud gave the same result. The nuts on other studs that had been cleaned with the die nut felt dodgy at about 15 lb-ft. The nuts on the other studs tightened satisfactorily to 20 lb-ft.
Was I using the correct die nut? The nut has the inscription 5/16 BSF. The Cornwall Austin Seven Club publish a list of thread types saying that cylinder head studs have BSF threads.
Is the answer - the die nut was made incorrectly?
When tightening the nuts with the head in place, one of the loose nuts sheared it's thread at a torque of 10 lb-ft. Trying a second nut on that stud gave the same result. The nuts on other studs that had been cleaned with the die nut felt dodgy at about 15 lb-ft. The nuts on the other studs tightened satisfactorily to 20 lb-ft.
Was I using the correct die nut? The nut has the inscription 5/16 BSF. The Cornwall Austin Seven Club publish a list of thread types saying that cylinder head studs have BSF threads.
Is the answer - the die nut was made incorrectly?