Stud size - Flywheel cover to Bell housing

[jedwards]

Gentlemen, my battle with studs and nut sizes continues.

I am keen to fit nice new nuts to the studs that hold the bell housing to the Flywheel cover, on my 1953 Series 1 80".

There are three different length studs involved, and are in the parts manual as 55778 (2 of), 3650 (10 of) and 3200 (1 of). The manual states that are 3/8" with no additional thread information, meaning that they should all be BSF.

However, (and there always seems to be a However) the tread is actually 16 Threads per Inch (TPI), which makes them either BSW or UNC. If it were in fact BSF, as per the Parts manual, then the studs would need to be 20 TPI.
My collection of 3/8" BSF 20 TPI nuts do not fit.

Taking the width across the flats, (which is around 0.600") suggests BFW thread as well. However those nuts have been blasted, re-plated and painted at least twice to my knowledge, so could easily be 0.562" across the flats, which would make them UNC. I also recollect reading somewhere in which a mechanics stated that they were UNC, but I cannot recollect where I saw that.

Can anyone she some light on their experiences with these studs?

regards
Jeff

[1950landy]

The stud should be BSW were it screws into the alum housing & BSF were the nut screws on. Any bolt / studs screwing into alum should be a coarse thread as fine thread will easily strip the thread out of the alloy.

[jedwards]

The stud should be BSW were it screws into the alum housing & BSF were the nut screws on. Any bolt / studs screwing into alum should be a coarse thread as fine thread will easily strip the thread out of the alloy.

Yes 1950 Landy, what should be and what is, are not necessarily the same thing. I have not removed the studs as yet, so cannot say what thread is used in the aluminium side, but the Nut size is certainly not BSF.

I suspect in fact that a previous owner or mechanic has swapped them out for 10mm Metric studs, which would explain the troubles I am having with Nuts.
I will explore further and report back when I happen upon a solution.

regards
Jeff

[russellrovers]

Yes 1950 Landy, what should be and what is, are not necessarily the same thing. I have not removed the studs as yet, so cannot say what thread is used in the aluminium side, but the Nut size is certainly not BSF.

I suspect in fact that a previous owner or mechanic has swapped them out for 10mm Metric studs, which would explain the troubles I am having with Nuts.
I will explore further and report back when I happen upon a solution.

regards
Jeffi have bell housings here jim

[jedwards]

i have bell housings here jim

Hi Jim, my issues is with the studs in the flywheel housing that holds the bell housing in place. My bell housing is fine.
regards
Jeff