4.2 VX TD Ticking noise - UK

[Toad555]

Hi
This is my first post on this US forum, so hi to everyone.
I've been posting on this subject in the UK but I'm not getting much response.

I have a 1992 Landcruiser VX Auto, its the 4.2TD engine 1HD-T.
The whole truck is mint except for this ticking/tapping noise thats been audible for some time, well for 20,000kms but its recently been getting worse.

The sound comes from the bottom of the engine right at the back on the exhaust manifold side and makes a noise similar to a stone in the tyre or tapping a coin on the windscreen. It can be heard at tickover is still audiable at over 2000rpm, it starts as the engine starts to warm up but I don't hear it from stone cold. At tickover the noise isn't regular, you hear 2 or 3 ticks then a gap of maybe a second or 2 then maybe a couple more ticks, then maybe 4 together, little bit like morse code really.

The engine starts fine and runs really smooth, there is no smoke or missfire and it doesn't use any oil at all. The odometer is displaying 103,000kms but being a Japanese import into the UK this could be incorrect but judging by the general condition it would seem to be about right. The engine is spotless inside and out.

So far I've checked the first obvious things, I've checked and replaced the big end bearings, they showed no wear at all but I replaced them anyway.
I've checked the valve clearances which are all a little tight. I replaced the exhaust front downpipe and checked for any manifold leaks or soot indicating a leak but could see none.

I've had the engine idling and loosened injector pipes one at a time to see if that made any difference but it did not seem to.

Some other forums have suggested loose torque converter bolts so I even checked them but did not find any loose.

Other "experts" have suggested the torque converter drive plate could be breaking up. My current worry is a wrist pin or piston slap.

One thing that could help me if no one has any immediate answers would be a diagram showing the oil pressure routes, ever since I replaced the big end bearings I've been wondering how the wrist pin gets lubricated, I was expecting to find a hole in one of the bearing shells with a hole up the centre of the con rod but there is none. Do they really just rely on being splash fed?

Sorry its an epic post but I wanted to get as much info in as possible.

Thanks
Toad...
UK