CP clutch hub centre nut

[Invicta]

Hi can anyone please tell me what size socket fits the clutch hub cetre nut on a 1950 model 18 with a CP gear box 69-X-2 or 11-7-11 I understand that the same nut is used on the later Burman gearbox also. I have searched and can not find any reference as to the size of socket needed to undo it. It clearly has previously been undone with a cold chisel, but I am more of a socket and spanner man than a hammer and chisel one. I do have some large sockets but none seem to fit. Any information will be greatly appreciated.

[dave16mct]

Seems to be 3/4" Whitworth according to previous answers on the forum, 33mm across flats. I haven't got one to hand to measure.
Dave

[Groily]

http://www.baconsdozen.co.uk/tools/conv ... charts.htm
The charts here are extremely handy for finding where the exact and 'close enough' overlaps are between different series of spanner jaws. I have a printed version on the shed wall . . .
3/4 BSW is right for the GB centre and therefore for the CP if it's the same nut - but I have used 1 5/16" AF in emergencies I think. Not having a 33mm socket . . .

[Invicta]

Thank you both for the information. however when I measured across the flats I measured 1.540" and even my bigest 36mm socket won't fit over it. Perhaps some PO has fitted a much larger nut.

[Groily]

That's a BIG nut at a bit over 39mm. Not a standard width for anything in the BSW department I don't think, falling between 7/8" and 1". Maybe a 40mm box spanner or deep-enough 6-sided socket would do it?

When faced with a similar silly size, I think it was on the end of a big Oilfield crankshaft, I made a mega 'adjustable socket' to get the thing off, with a big enough hole to allow the outer end of the shaft to pass (because an ordinary socket wouldn't go over it). Lot of work for one thing though (I know I should get out more and/or should have had the patience to wait for a tool order to ship!), and one would have to be designed to go in the basket and grip the thing firmly.
Good luck and hope the cold chisel treatment can be avoided (or a new nut sourced after demolition).

adjustable socket 1.jpg

[Invicta]

Hi I just went and re measured the nut,(with my glasses on} and it is 1.5" across the flats , which equates to a 3/4" BSW socket, which I have now ordered. Thanks again to all who repied. As I am buiying a new nut I may use the PO's method to get it off while I am waiting for the new socket to arrive."

[Groily]

Hang on a sec!

If it's 1.5" across the flats it's NOT a 3/4 BSW socket you want. (EDIT- To get this one off) (If it were 1.3", then you'd be OK . . .)

See this pic:
*one Burman mainshaft (GB version)
*one socket clearly marked
*one correct old nut - which the socket fits nicely - and
*a decent vernier gauge showing a precise 1.3" AF (correct to a thou or two on the vernier's attached clock, not shown in the pic)

Burman mainshaft nut.jpg

[Invicta]

My 3/4" BSW socket at last arrived today and of course it does not fit the clutch centre nut, it is far too small. So clearly my clutch hub nut is much bigger than that fitted to a Burman GB version. My 36 mm socket won't fit so it must be a 38 mm socket that might fit, but it would be nice to know the size of the correct imperial socket that fits.

[Groily]

It wouldn't, for reasons already stated.

Not sure, but your nut may be incorrect in AF terms if it's true that Burman CP and GB mainshafts used the same, per dave16's first response to this.

You said initially 1.540" AF, then 1.5", both are WAY over 3/4 BSW and in neither case is there a BSW/F size that suits (see tables posted previously). 1.5" AF will of course fit nicely and is a 'size'.
A 38mm won't go so don't buy one of them as well unless you need it for something else. A 39mm (?if an available size?) might just go on. Otherwise it's a 40mm box or six-sided socket as mentioned before, and hope for the best despite a bit of 'slop'. But a socket that big is probably a 3/4" drive job, so best avoided unless you have the drive tools, as they aren't cheap.

(Or whack it off off/ split it with a chisel like the last bloke, and get the correct new nut to replace it, whatever that might be exactly. It should / must be a size for which there is a spanner, at least!)

[Harry44]

How about this ?

https://www.ebay.co.uk/itm/360472239668 ... R9aBkNfVYw