I am replacing some of the bolts attaching the gearbox outer cover to the gearbox shell. According to items I have read, the required bolt size is ¼"BSF, so I ordered some, which arrived today. Upon opening the package, it soon became apparent that the bolts supplied, as per my order were not correct. Despite the invoice stating they were the ordered ¼"BSF, the thread was much too fine. It looks more like BSCY to me. Are all boxes the same, or did, perhaps, Norton/AMC change the thread at some stage? My gearbox has the serial number NA6904 stamped on it, which I seem to recall from earlier observations, makes it about 1964 vintage.
It seems to me that the required bolts should have the same thread as the timing cover bolts on the engine. Any ideas, please?
Bolts ??. Neither the inner…
- Log in to post comments
1/4" BSF and 1/4" Cycle have…
1/4" BSF and 1/4" Cycle have the same pitch, at 26 threads per inch.
That is a fine thread.
- Log in to post comments
Their thread angles are…
BSF and Cycle thread angles are different but suppliers seem to consider them to be interchangeable.
Fine threads are more secure because the wedge angle is shallower.
(Edited to remove confusion...Whitworth is much coarser for use in alloy)
- Log in to post comments
Neither BSF nor Cycle will…
Neither BSF nor Cycle will fit in a Whitworth threaded hole.
- Log in to post comments
Cover Screws
What is worth a mention is the Heavy Twins Gearbox Cover Screws and Engine Timing Cover Screws. These look similar but.....
GEARBOX, AMC.
Inner case studs, short (5) 5 /16” 26 +22 - 1” Slotted Cheesehead.
Inner case studs, long (2) 5 /16” 26 + 22 - 1½” Slotted Cheesehead.
Outer case screws (5) ¼” 26 - 11 /16”
DOMINATOR TIMING COVER
Screw, short. (6) E6980 ¼” 20 1” - Slotted Cheesehead.
Screw, long. (6) 10940 ¼” 20 1¼” - Slotted Cheesehead.
- Log in to post comments
Bolts ??. Neither the inner cover or outer cover use bolts . I suspect you mean studs and nuts?. Each stud will have two thread forms usually whitworth where they screw into alloy and bscy for the nuts that secure the inner cover. The Nuts can be usefully changed to a reduced hexagon type to allow a socket set to be used .So much easier if you have to work on the box in the future.