Thread of big end bolts and nuts?

Derek 328 · #1 (**permalink**) 07-05-24, 11:25 AM

Hi

I have a 3/8 BSF x 20 tap and die. This corresponds with the thread gauge on the stud.
BUT when I gently put either the tap (on the con rod) or the die (on the stud) it tightens and it is visibly shiny on the thread.

Can anyone shed any light as to why this is happening.

Why am I doing this? I have a con rod with a hole into the oil way just below the small end!!! I have sourced a con rod with no studs. Just want to move the studs from one to the other.

Furthermore, I need a set of new nuts, where can they be sourced, of the correct quality?

Thanks

Derek

flyinghorse1 · #2 (**permalink**) 18-09-24, 07:30 AM

Did you solve the problem as it would be interesting to know the issue.
Whit and Bsf have 55deg thread angle.
Unf is 60deg, plus the tpi is different between 3/8 Bsf and 3/8 unf ( 20 vs 24)

Derek 328 · #3 (**permalink**) 18-09-24, 05:39 PM

Did not solve it, just screwed the big end bolt in. I have learnt that a stud is best made with a tighter thread in the end that would go into the block or end cap. A looser thread is used for the nuts to tighten. An engineer told me, who made a new stud for a main bearing which had been mauled by someone with a stud extractor.