The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: KiwiGF on 10.04. 2011 02:54

Title: Cylinder base studs and nuts
Post by: KiwiGF on 10.04. 2011 02:54

The studs I've got look wrong they have whitworth threads both ends (my engine has been upgraded to thick flange barrel).

I've some other studs off a spare set of 54/55 cases but they are possibly a bit short so my questions are:
how long should the studs be?
how much stud should stick up above cases?
should the top threaded portion be whitworth or a fine thread?
should washers be fitted?
Should the studs be loctited into the cases?

The studs I've got are 1 3/8 long

Thanks !

Title: Re: Cylinder base studs and nuts
Post by: trevinoz on 10.04. 2011 03:00

Kiwi,
             The studs should have 26TPI threads on the top portion.
Length I can't say but if you look in the table I posted some time ago the info may be there.
  Trev.

Title: Re: Cylinder base studs and nuts
Post by: Beezageezauk on 10.04. 2011 09:57

Hi Kiwi, 

As Trevor says the top threads should be cycle thread (26TPI) and the bottom threads should be Whitworth.  Measure the difference between the thickness of the thin flange and the thick flange barrels and add this figure to the length of your original studs.  I reckon that this should give you the length of the studs you need.

Beezageezauk.

Title: Re: Cylinder base studs and nuts
Post by: chaterlea25 on 10.04. 2011 13:16

Hi KiwiGF

how long should the studs be?
how much stud should stick up above cases?
If you are making your own, as much thread as possible into the crankcase. then barrel flange washer nut + 2 threads app


should the top threaded portion be whitworth or a fine thread?fine

should washers be fitted? yes (plain)

Should the studs be loctited into the cases? no need if the case and stud threads are good, make sure they are

HTH
John

Title: Re: Cylinder base studs and nuts
Post by: Goldy on 10.04. 2011 13:51

The basics to any fastner is that the thread depth should be the same as the thread diameter and so a 5/16" nut will be 5/16" thick. There is no strength gained from making this any more so you coudl make the nut 2" thick and it would not be any stronger. so you can calculate any stud/bolt length by the length to be bolted + diameter + 1/16" for the washer + 1/8" for appearance. With the tapped hole into the crankcase, although there is not strength gained there is a mechanical advantage in having more thread due to the soft alloy material and as others have said in this case the stud depth is 1/2".

Title: Re: Cylinder base studs and nuts
Post by: KiwiGF on 11.04. 2011 12:00

Thanks everyone, I need some new studs then, as they should be cycle thread above the case. For the record I reckon the stud should be at least 15/16 above the case and at least 1/2 in the case (I could go up to 5/8 with my cases), so the studs I have off a thin flange engine are just a 1/16 too short at best - just another item on the huge parts order I will have to place on some lucky vendor .......

Title: Re: Cylinder base studs and nuts
Post by: iansoady on 11.04. 2011 14:13

Interestingly, Velocette (whose aficionados claim you need to be an engineer to ride one) used studs threaded 5/16" Whit at both ends for the magneto fixing to the timing chest. Confused me no end.