8 replies to this topic

[danny5686]

Any guys on here know where I can get a tap for the crank thread flywheel end? I believe it is 5/8 - 16 whitworth. I've had a look on the net and some people want £50 which is ridiculous!! Any advice would be great!!

[Ethel]

There's an epic thread on this. I believe Guessworks had some made up, dunno if he has any left. It'll be a similar price, it's not a common size.

[tiger99]

I think you should use the search facility, or if necessary Google, as there have been a few discussions, perhaps better called flame wars, about this very subject here not so long ago.

The controversy usually hinges around whether it is a Whitworth or Unified thread form, and although the pitch of Whitworth and UNC is the same in most diameters, thread form, including angle and the tip/root clearances, is not

[dklawson]

NO... not again!

Regardless, contact John at Guessworks and see if he cannot help you out.

[tiger99]

The strange thing is that I can't remember the outcome of the debate, although I usually remember facts like that. Maybe I was just not convinced that anyone was right, or that the thread was always the same on every engine, like the mysterious CV joint threads.

I remember getting as far as thinking about the many problems people were having with the taper at that time, and wondering if perhaps the root of the problem was that the bolt did not go in deep enough, so when torqued up it stretches the crankshaft, reducing the angle of taper, while compressing the flywheel, so increasing the angle of its taper, so even a lapped flywheel does not make good contact with the crankshaft. I thought that it might be a good idea to drill the thread right out, and bore deeper, almost to the plane of the teeth of the primary gear (it is probably safe to go right to the nearest end of the main bearing), retap and fit a longer grade 12.9 bolt. In that case it would be tapped with a readily available thread, like M16, correcting the torque for the different pitch if necessary. That might solve two problems, getting the correct tap, and preventing the taper loosening. Next time I have a Mini, hopefully soon (still no garage...) at the first sign of trouble in that area I intend to try that modification.

[Ethel]

I think it went on so long because there was no definitive answer

The consensus was it was a Whitworth thread form iirc.

[Guess-Works.com]

It is a whit' form thread....

I've basically rented mine out before, costs as follows...

£10 + post + vat + £50 deposit.... when I get the tap back you get your £50 back

or £66 if you want it all added up...

[dklawson]

As John said, the outcome of the debate was that the thread is as specified in the factory manuals "Whitworth Form" but not a standard Whitworth thread size..

[tiger99]

Thanks! I will hopefully remember that next time.