Big Twin Gear Box Bottom Studs

[TimR]

In the parts manual there are 3 different bottom studs listed for big twin gear boxes.


/tmp/PreviewPasteboardItems/Spare Parts 41-54 (dragged).pdf

Page 66 of my 1941 to 1954 parts book


Part # 34722-36 1937 to early 1947 big twin 3/8-16 X 3/8-24

Part # 34723-47 late 1947 to 1954 big twin 7/16-14 X 3/8-24

Part # 34724-36 1937 to 1954 oversized big twin 1/2-13 X 3/8-24


Does a Shop Dope explain the reason for change in size some time in 1947 of the stud? Was the 3/8-16 failing in the case? From the looks of things cases 1946 and earlier have the possibility of 2 steps of oversize. What have you experienced?

[Jerry Wieland]

What happened is this. Prior to mid 1947 the standard bottom studs were 34722-36, 3/8 - 16 x 3/8 -24. Mid 1947 and newer the standard bottom studs were upsized to 7/16 -14 x 3/8 - 24.

I did some research on this 20 years ago or so and I was thinking that the early oversized studs became the new standard stud in mid 1947 but your information seems to imply that the oversized studs were always 34724-36, 1/2 - 13 x 3/8 - 24 and that just the size of the standard studs was increased. The increase was only on the end of the stud that screwed into the aluminum case.

It is not uncommon to find the threads in the case stripped so I suspect they were just trying to cure a problem.

Jerry