Any ideas on what the thread in the end of a mag engine crankshaft is?

Which end? Can you be mores specific? Some of the early mag crankcases had fine threads rather than coarser later types. What year is it?

Cheers

R

Can it not be simply measured, the diameter and TPI etc?

To the best of my knowledge:

5/8" 16 tpi Whitworth form (Special) on front

7/8" 12 tpi Whitworth form (Special) on rear

Before you go ordering special dies etc (they cost a mint!) I would be inclined to take Hedd's advice and measure them.

Regards
Barry R.






Regards

Barry R

Have just had a look on that fount of information for things A7, The Cornwall Club web site, and have had a look at their "Screw Threads" page, which confirms crankshaft thread details on 1932 engines.

The particular page is:
http://www.austin7.org/threads.htm

I am now just a little concerned that the details I gave, while correct for later engines, may perhaps be different.

Perhaps out of all this confusion, when the absolutely correct details are able to be confirmed, the Web Master of the Cornwall site might be able to be contacted (as invited on the site) and that further wisdom be then added to Cornwall's most useful archive.

Regards,

Barry R.

I think you'll find the Cornwall Club's webmaster keeps a very regular look at these messages and contributes as well.

Sandy

Sorry, it is the thread in the front of a 1928 1 1/8 crank, I dont have a spare starting handle bolt to check,bit difficult to check inside the crank end itself though.Suspect it may be one of the 'Austin' specials like on the halfshafts.

Even so it should be pretty easy to measure, use a thread gauge to get the TPI, (or even a thread file if you dont have a thread gauge) And you can fairly simply best guess the diameter. It'll be a fraction. Pick the nearest to your rough measurement.

Ian

Further to what Hedd advises, you may find it easier to make a mould of the thread form, i.e like the bar of soap and prison key principle. Maybe just a bit of plastacine pushed in and carefully pulled out will allow you to gauge the pitch. A drill shank pushed into the hole would gauge the minor diameter and you could then educated guess the actual size. When I worked in a calibration lab we often took casts of difficult to measure threads

Of course hopefully a knowledgable person from the forum will no doubt know the answer

Steve

Thanks for all your help guys, I lent my thread gauges to someone years ago and never had them back, and cant remember who had them. Was hoping someone might know for sure what thread it was.

I think that it's one of Austin's long serving "admiralty" threads.
The story goes that they bought so much kit during the Great War for naval contracts that they continued to use it after the war - right up into the A series.
During the Great War admiralty threads were fixed pitch - 16tpi if I remember correctly. Admiralty fine is 20tpi.

1/2" BSF is 16tpi so you can easily check it using a 1/2" bolt as a thread gauge.

Charles

I might be wrong but I'm sure the thread continued on the starting handle dogs/crankshafts on early A Series engines (early Morris Minor, Austin A30 etc.)

STEVE