Flywheel Bolt Thread: UN or Whitworth?

[ianh1968]

Both ends of an 'A' Series engine crank have the same thread.

It is 5/8" by 16 TPI (Threads Per Inch).
IT IS NOT 5/8" UNF (18 TPI) !!!
This is fairly well known, but what is the thread type supposed to be?

Is it 55 degree, round top/bottom "Whitworth" (British),
or 60 degree, flat top/bottom "Unified" (American)?

I suspect that the thread is 5/8" by 16 UN as most of the other threads
on the engine are either UNF or UNC.

Some of the "fluid" ports use "pipe threads", others don't:
The oil pressure outlet thread is 1/8" NPS (Straight), for an 1/8" NPT (Taper) adapter. (American)
On pre 1990 engines, the oil filter head is 1/4" NPT for the feed pipe. (American)
On pre 1990 engines, the oil pipe banjo bolt is 5/8" UNF. (American)
After 1990, both ends of the oil pipe changed to 11/16" UNF. (American)
The rear block water drain bung is 1/4" BSPP. (Parallel/Straight). (British)
The oil pressure relief valve is 1/2" BSPP. (Parallel/Straight). (British)

Are there any "Thread-Nerds" amongst us?
Please post corrections if any of these are wrong and I'll amend the thread. (Sorry!)

[Smiffy]

It's WF, 'Whitworth Form' tells you in the BMC manuals.

[ianh1968]

Thanks, Smiffy!

What's left of my Dad's old "Austin Seven Workshop Manual" is archived out in the loft, I never thought to check in there...

I must confess that several years ago I did acquire a 5/8"x16UN tap and have been using this to "clean out the threads"
of various cranks. Maybe the threads in the crank are machined a bit sloppy as using the "wrong" tap has always been
successful...



Ian

[Smiffy]

I must confess that several years ago I did acquire a 5/8"x16UN tap and have been using this to "clean out the threads"
of various cranks. Maybe the threads in the crank are machined a bit sloppy as using the "wrong" tap has always been
successful...
Ian

You wouldn't be the first, even 'Mini experts' where under the same impression until a few years ago...........

[Spider]

Are there any "Thread-Nerds" amongst us?

Yes I have to confess....

The Crankshaft Threads ARE actually British Small Arms Thread

http://www.mokesinc.org/index.php/topic,9692.0.html

[Tim]

It wouldn't be that small an arm if it has to use those chunky big threads.

Tim

[Spider]

It wouldn't be that small an arm if it has to use those chunky big threads.

Tim

Tim buddy, your right mate

Maybe they've reacher's disease? Small arms and deep pockets


Oh damn, that short arms

[251 ENG]

The thread is 5/8" 16tpi WHIT form .

Use to work somewhere that had 100,s of taps that came from Morris engine,s when it shut down .

[ianh1968]

Well, it looks like Whitworth won...

Thanks for all your suggestions.

Does anyone know where I can buy decent hex-headed crank pulley bolts of a sensible length?

Presently I have Allen screws, but I think that a proper hex with its larger contact area would be better.

[Smiffy]

Well, it looks like Whitworth won...

Thanks for all your suggestions.

Does anyone know where I can buy decent hex-headed crank pulley bolts of a sensible length?

Presently I have Allen screws, but I think that a proper hex with its larger contact area would be better.

Use a verto one and cut it down, took about 3/8 inch of mine iirc

[ianh1968]

Thanks, Smiffy...

Great idea to use a Verto bolt!

Do you know what the A/F size is? Is it metric? (I hope not...)

[Smiffy]

Yeah it's metric, 30mm