I'd be inclined to replace the CPS. They aren't expensive and are one of the few things that will stop you dead in your tracks.

OK well here are the pics:

I straightened the central pin of the CPS as a temporary measure. It has also got wear marks on it so needs changing.

I also straightened the bent teeth. Initially I hadn't bent them back enough and had a very light tick... 1mm more and it was all silent again.

I was very hopeful.... engine quiet as a mouse.... left it running as it hadn't been started for a week and the battery had needed charging.... then...

Engine warms up and.....

CLACK CLACK CLACK

Absolutely no change at all!! I think I just happened to find the bent bits, and these had no connection to the clack at all! The engine does run a bit smoother now, and thinking about it he had lost a tiny bit of pick up power (although at speed no change).... so now I am at a loss AGAIN! Really fed up! :-(

I fully understand that this drives you mad. Do you have access to a ramp? I'd say run it hot, quickly remove all sparkplugs and let someone turn it over while you listen underneath. (and have look if it was the only bent tooth).
It's not much but just trying to help.

I took off the fan and used my torque wrench to turn the crank while I had the cover off... there was only that one bent tooth. Also when I bent it back but it was touching it was a very different noise, more tap than clack. Plus it happened straight away.

This clacking noise is definitely not there when cold at all. Also if I raise the revs very slightly it doesn't get louder, in fact it seems to get quieter! It's still faintly there, although let's face it the V8 is not a completely silent lump anyway.

The thing I don't get is that most noises caused by wear are there when cold as the tolerance is higher, then as an engine warms it expands slightly and the tolerance lowers... unless I am getting is wrong? Unless it's caused by the oil thinning as it heats up? Initially I thought that and that's why I did an oil change when it first happened.

Ferryman - what will popping the plugs when hot and turning over tell me? I'm keen to learn as my little K-Series TF is a very different beast to this V8!

Popping the plugs and turning it over means there is no disturbing noise from compression and drag on startermotor, the engine just turns smoothly apart from the hissing plugholes, that's why.
Tony.

Ah OK makes sense.....

I'll try and give it a go tomorrow as alone today!

OK so finally my usb camera arrived and I had a good look around in the bellhousing (as best I can anyhow). I couldn't see any obvious 'rub' marks etc - and the 'bent back in to shape' CPS seems to be missing all the flywheel teeth - and anyhow it's a different noise to the tapping that occurred when they were touching.

I ran it till it warmed up and the noise started again - as soon as it got hot - before that it really is silent Listened all over the engine with a long screwdriver and the loudest 'feedback' is deifnitely coming from the bellhousing - you can hear the noise through the screwdriver alsewhere on the lower end, but it is noticeably louder there, and quieter the further forward on the engine you go. It's really really odd though. On tickover (that is slightly lumpy) the clack is much worse.... speed it up and it gets better. I am feeling a engine/gearbox separation is the only way to tell now.... losing the will to live!

Is it possible to run the engine when it's not connected to the torque converter? I am thinking that would tell me once and for all if the noise is the gearbox end or engine?

If it does turn out to be in the bellhousing then there really isn't much in there to cause a clack right? Flywheel to starter touching (pretty sure I didn;t see any wear with my little camera so unlikely), CPS to teeth (but I am pretty sure that is sorted and a differemt noise), Flex plate (the suspect but then how does it 'clack' on anything? Plus it gets no worse or better when putting in gear) or I guess a loose bolt that's touching somewhere when hot (but then surely it would get worse when revving?).

I am sorry for all the questions - it's driving me nuts as I keep the old boy on a budget for the sake of my mum (plus I love him to bits), otherwise I'd have something reliable like a Honda!

OK ... I'm back! Been so busy (and had the use of my mates lovely MGZS (which he now says he's giving me in November when he finally moves!) that I havne't had a chance to move on with this.

So yesterday afternoon I went out and started to remove the radiator and bits so I can jack the engine up, remove the engine mounts, and split the engine box so I can see the bellhousing interior. For some reason I can't get the viscous fan off (which way should I be turning it to undo - as I tried both!?), last time my huge adjustable and a mallet got it off! So you can imagine gettin teh rad out was a bit of a pain, but eventually I eased it out. I loosened all the air con and oil cooler rads so they move as far forward as possible.

Also took off the heater pipes, and anything else that stopped the engine moving forward.

Today I'll undo the passenger (RHD) manifold to downpipe, and the drivers manifold to head (as I can't seem to get to the engine mount bolts with the drivers side in place!). Then I'll undo the flex plate to torque converter bolts, and the lower bellousing one apart from one (to stop it flexing and cracking anything), then it's jack the engine up and remove the mounts. Then finally I can lower it down, remove the top bellhousing bolts (and the lower one I left in) and separate things. I REALLY hope I find something otherwise from what I've been reading, it could be a slipped liner or something.

I've also been on the lookout for any local 4.6's going cheap as 'spares or repairs' just in case I need an engine! Wish me luck!