OK I think I can finally draw a line under this refurbishment.
I managed to fit the replacement tipping ram spool valve. It had a totally different mounting lay out, so I had to make up an adaptor plate taking the original valve's mounting points and presenting tapped holes to suit the new one. Fitted nicely and I managed to get the operating rod in the same alignment as the original, just having to shorten it a bit.
Now the hydraulic ports were another matter. The original was BSP all round. The second hand replacement had a very odd coupling that I've not been able to identify - 20 tpi, but an o/d of 0.758" with a deeply recessed conical seal. No matter, the body of the valve was tapped 7/8 UNF on all ports, so it was a matter of sourcing 7/8" UNF conical male to 1/2" BSP conical male adaptors for input and output, and 1/2" BSP ones for the A & B ports of the tipping ram. All went together nicely, and I even got 'tip' and 'retract' the right way round on the spool valve (50/50 chance !)
So I thought that I'd replace the weeping sealing in the tipping ram itself. I put the skip into 'full tip', then extended the fork lift tines above it and secured the skip to them with strops. This let me safely disconnect the hydraulic pipes to the cylinder and knock out it's pivot pins - heavy bu@@@r
I've had the seals waiting for some time but have been putting the job off. The outer end of the rod is a design I've not encountered before, with the end cap retained by a heavy C ring. All the was visible from outside was a large circlip preventing the cap sliding into the cylinder. Turns out, you remove the circlip, push the end cap inwards leaving the C ring in its groove, then remove the ring. Clever design.
Replaced the piston and rod seals, put it all back together then cleaned it up and sprayed a couple of coats of zinc rich primer followed by satin black, as I did with the steering ram. Back on the dumper and it works a treat.
In a fit of enthusiasm I decided to sort out the 'rotating skip'. The skip sits on a massive thrust bearing, and is prevented rotating by a large pin that is spring loaded upwards, and released by a foot pedal. It's never worked in the nine years I've had it. If you managed to release the pin, it would stick down and be a problem relocating. After a bit of cleaning up, cooking with a propane torch, and jiggling about, it freed off enough to withdraw it and give it a good greasing.
This has allowed me to rotate the thrust bearing and re-pack it with grease. Easy enough to turn it unloaded, not sure what it will be like with 2 ton of rubble in it
So - that's about it - well I've a wheel and tyre to replace as one on the front axle is off a one tonner and a bit narrow - I've got the replacement (good old eBay) - just a case of doing it