Water pump fan mounting studs 1989 xj40

[onside405]

I have a 1989 XJ40 4.0 and have just fitted a new water pump

Can anybody clarify exactly what size the nuts should be that attach the viscous coupling to the water pump studs?

They should be 13mm, but a 13mm spanner is loose and a 12mm doesn't fit.
A 1/2" just about fits, very tightly, if tapped gently onto the nut.

The water pump looked original and the nuts were very tight, resulting in very slight rounding of corners when undoing them with a 13mm spanner. The spanner is good quality and a sliding fit on other 13mm nuts.

Were there any imperial threads/nuts still used on this model?

I have been working on cars for over 50 years and have never experienced such a strange thing

[mike020150]

The only reference I can find to these fixings, is the use by Jaguar of 8mm flanged nuts plus washers, which may suggest that someone else may have been there before you. If, perhaps the studs had been damaged previously, they could have been replaced with non standard items. Mike.