Getting to the bottom of it...

Well, last night we removed the engine again and split the cases. No great problem - oil mess on shed floor.

Not a very good pic I'm afraid. Interesting piece of debris:

It's metallic, the curved edges are as cast and the straightest edge is a fracture. We shall see no doubt.

So the cranks are out; I have started to clean up the front crank:

The timing side journal is good (dimensions shown in the Engine Tolerances page) and the rods look good too. You might recall that No. 1 small end bush is out of position and the oil hole does not line up.

The big ends feel OK, No.1 rocks considerably more than No.4. I will need to grind down my 1/4" BSW socket to allow it to fit the big end nuts - I have already mauled a tube spanner. The oil pressure relief valve had a large chunk of debris in it - rubber or carbon, I'm not sure which at the moment.

Next was the sludge traps. The plugs came out with the impact driver & I consider that a lucky break. Full of carbon though:

However, I poked a 5 mm twist drill into these and the carbon, approximately as hard as clay, was quite easy to remove.

It was obvious from the resistance, and the consistency of the goo coming out that the carbon extended down to the big end oil ways (cross drillings) and no further. At this point, the goo was very oily and no more solid came out.

When I removed the opposite plug, exactly the same sequence of events and when both were clean I was able to poke a bit of welding rod down the drillings, right through the crankshaft. 

It's not a straight hole - they are obviously drilled from either and and meet in the middle.

So, there is not much more I can do with that until I can remove the big ends. Then I can clean out the smaller big end drillings and properly clean the main bore through the middle.

I haven't really looked at the cases yet. When I removed the sump plate ('Very flat, Norfolk') there were flakes of white metal in the primordial ooze. These came from the timing side mains:

I was aware that these were shot from the movement on the nut. Now we have to find someone to replace and line-bore them!

More later.