Camshaft Pulley Nut

In common with the nuts on some other critical components, the camshaft pulley nut is designed so that - once correctly tightened, it's edge can be 'staked' into a little receiving groove on the shaft. That 'staking' stops the nut working loose.

Any work on the car that involves removing the pulley, means either grinding that dink off, or trying to 'un-stake' it with a screwdriver or similar. Then, of course, when you want to refit the nut, the 'dink bit is either missing or damaged and weakened.....

My pulley shaft and 'staked' nut

The more you remove the pulley, the more unusable the nut becomes.You could pack out the nut with extra washers so that - when the nut is tight - the bit to be 'staked' is different but then the nut is not fully threaded onto the shaft , which potentially represents a weakness. 

I decided to fit a new nut. The usual DS parts suppliers sell a modern 'nyloc' nut for this job, but they aren't cheap.The shaft thread size is M16 x 1.5 pitch - so that is the size of the nut needed. I went around the corner to my local fixture specialist and bought a nut for just 25p. In fact I was so embarrassed at only spending 25p, that I went crazy and bought two for 50p!

Camshaft pulley 'nyloc' nuts

That felt better. And it was a saving of £8.50 over the £9 if I'd bought them elsewhere. 

Except it wasn't a saving. it was a loss of 50p!! When I came to fix one of the nuts, I discovered that it tightened against the pulley before the nylon part of the nut engaged with the threads of the shaft - meaning the 'nyloc' nut wasn't going to 'loc'....For the nut to lock, the pulley would need to have been further along the camshaft. Or the shaft would need to be further forward. That simply wasn't possible and - even if I could remove any shims to get the pulley further back - it would have meant it was out of alignment with other pulleys on the car.

Shim behind the pulley - used to align pulleys and belts

What I noticed was that the very tip of my camshaft - where the little groove to receive the 'staking' was - was not threaded. You can see in the photo above. The end of the camshaft was thinner and smooth. There was nothing there for the nylon in the nut to bite in to. Perhaps the ends of the camshafts were this way so that any 'staking' did not damage threads on the shaft when the nuts were removed? 

Anyway, it meant that my 50p had been squandered. And I still had the problem of sourcing a proper nut with a collar that could be staked. I asked questions in a Facebook group and got several helpful replies. The advice was to buy a hub nut for a trailer stub axle. Some quick Googling confirmed that this looked to be the way to go. 

Hub nut for a trailer stub axle

They weren't cheap - especially when you factored-in postage - but I splashed out and bought three so that I had spares! They've arrived now and look to be just what I need. 

Trailer hub nuts

The only difference is to the collar - the bit that get's staked. The proper DS nuts are machined around this part - possibly to make the metal a little thinner and more maleable? By comparison the hub nuts retain their rough cast shape and look to be thicker-walled. 

Are the walls thicker?

But they are designed to be staked, so I'm not worried about that. I can't justify being a lathe to machine these nuts down a little - but I might just try and catch my mate Peter on a good day and see if he'll do it for me.

I was still left wondering why a DS parts supplier sold a 'safety nut' (a 'nyloc' nut) that wasn't fit for purpose? The parts book relevant to my car shows a collared nut for staking and a groove in the camshaft end.

I have another spare DS camshaft. I dug it out and was surprised to find that the threaded end is different. the thread goes all the way to the end and there is no groove for staking a nut.

Other camshaft - threaded to the end

You can see how that end is different to my (fitted) camshaft.

Camshaft on my car

I've got no idea why my spare camshaft is different, but it looks as though a 'nyloc' nut would work just fine with that other type of end. There was a change to the nut in June 1971, as documented in parts manual 604.....

A change to the nut from June 1971?

......but not an equivalent change in the camshaft part number. And the change to the nut can't simply have been a 1mm reduction in length can it? Citroen catalogue 645 that shows the sizes of fixings lists the post June 1971 part as just a standard nut? Not collared or even a 'nyloc' nut.

The catalogue does have a section listing 'nyloc' nuts but part 'ZD 9525 000 W' is not listed  there.

Citroen 'nylstop' nuts 

So in conclusion, perhaps a word to the wise: if you are looking to replace your camshaft pulley nut, look for the groove on the camshaft end for staking and whether the threads on the shaft go all the way to the end. If there is no groove, a 'nyloc' nut will probably be fine - but check the thread 'bites' onto the nylon. If there IS a groove then seek out a trailer hub nut and stake it to the shaft.