Time for another update!
I'm conscious that this mght be a bit boring for the experienced Morini engineers, but I also hope some of this will be helpful to other newcomers like myself - it's certainly a voyage of discovery for me!
Back in the 1970s oil filters were uncommon on motorcycle engines and crankshaft sludge traps were common. The idea is that metallic particles etc would be centrifuged out of the oil stream and collected in the trap. I don't know why, but the plugs are always difficult to remove and the Morini was no exception. There are 3 plugs on the 500 crankshaft and the large one eventually came out with an allen key. The two smaller ones had to be drilled out, thus ensuring that the crankshaft was covered in metallic swarf!
Initially I thought the sludge traps were clean, but they are in fact quite a bit deeper than I thought. I used a drill to remove the sludge deposit, which was about 20mm deep:
To get all the crankshaft oilways really clean is a bit of a poke and hope job because you can't see if they are clean or not. I used several generous shots of carb cleaner and compressed air. When nothing visible was coming out, I pumped in a lot of oil and started to reassemble.
I was very lucky to be able to borrow a cutaway R/H crankcase half, so the next job was to reassemble the gearbox and adjust it. I had carefully cleaned all the gears, etc, so I double-checked the assembly order against the parts book. There are so many plain washers, splined washers, circlips and so on, there are numerous opportunities to make a mistake! The selector stop plate needs to be adjusted on its slotted holes so that the selector pawl travel is equal in both directions. The travel needs to be enough for the detent arm to drop into its grooves without starting to climb up the other side. This adjustment is easy - if you have a cutaway crankcase. You can now check that all gears can be selected cleanly and neutral has a positive stop.
The crankshaft is now re-fitted to the L/H crankcase with the nut on the oil pump drive gear done up as tight as you can with the crankcase open. The important thing is to close the two halves of the L/H main bearing so that the crank is properly located. I found it easiest to fit the camshaft into the R/H crankcase first, but I think it can be done either way. You really need an oil seal protector for the R/H end of the camshaft, doing it without needs a lot of care and patience. A final check and the R/H crankcase should slip on quite easily.
And that's as far as I've got. So far so good. All gears still engage correctly and easily and the crankshaft turns smoothly without play in any direction. I'm hoping to get a couple of hours on this tomorrow. In the meantime, does anyone know if the barrels and heads can be re-fitted with the engine back in the frame? If so, that will allow me to do a lot of reassembly while I'm waiting for the heads and barrels to come back from being skimmed and having new valve guides fitted.