I slotted both hornplates from the top down, wide enough for the bearings to slide in (I made my bearings in one piece out of cast iron).

This allows the complete crankshaft/eccentric/bearing assembly to be dropped in from the top – this makes it much easier less difficult to set the eccentric timing and connect everything up.

I did it this way after seeing a full size engine (I forget what make) which had a similar arrangement, so I reckon it’s a legitimate solution.

The pump eccentric just slips onto the short end of the crankshaft. It does not go between the two webs, that is where the conrod goes and is why the conrod has a split bearing.

The off-centred bit is called the crankpin or big end journal, and the two odd shaped bits are the crankpin webs (there are probably other names in both cases, but I can’t bring any to mind just now*).

*And whatever you call them, someone is sure to say ‘That’s wrong! They should be called…’