We have started: the engine and the cylinderhead are at the overhauling workshop and the first parts have been ordered. The goal: to build a 1000cc engine (or roughly that size....) for the Fiat 850, using an Autobianchi A112 Elite block; it's 965cc and and will be drilled 0.6mm over to get 982cc. The bore is 67.8mm and the stroke remains 68mm.
The block I bought is completely empty, as if it just came from the foundry. Crankshaft is in good condition, no machining is required. I have connecting rods, but no pistons, which is why the choice for a larger bore was easy.

850 A112 blok

The cylinderhead is something else. A previous owner has been working in the inlet channel with a dremel. I'll have to wait and see what the effects are. And as with any genuine Fiat 850, the combustion chambers of the first and fourth cylinder are pitted. Never seen a used head without burn-in around the valve seats. 

850 A112 kop 1 850 A112 kop 2

The idea is to have larger valves installed because of new valve seats. The current inlet valves are 29mm, the exhaust valves 26mm. I am thinking of having valves from a Cinquecento fitted: inlet valves of 30.5mm, the exhaust valves of 27.5mm. Not too big and there should be enough space for it.

Of course I also have to keep going and make sure that I use my own stock of parts before I order new parts. I already have a lot of NOS-parts and also a number of used ones: that's what I started with.
First item found: the rockershaft.
The average Fiat 850 normally has a tough last year of use: little or no maintenance. And when the engine is taken apart, there normally is a thick black layer of sludge on the inside. And thats also present on the rocker shaft I had in stock. Side-effect: it can no longer rust.

850 tuimelaaras 1
This is the rockershaft when it came out of storage. Looks useful but nothing is movable anymore at this stage.

850 tuimelaaras 3

I was able to take it apart and then cleaned with a lot of elbow grease and penetrating oil.

850 tuimelaaras 4
The shaft with a lot of oil residue.

850 tuimelaaras 5

850 tuimelaaras 6

After a lot of brushing, fiddling and rubbing with wet 1000 grit sandpaper, this is the result. The bores were opened by hand with a small drill, after which the interior was soaked in solvent for a few hours. Blew  through all holes and then checked one by one: with duct tape, masked off all but two holes and then blew through. Tape other holes and repeat.
At least I'm now sure oil can get in when the engine is running. And for the purists among us: no part of this rockershaft touches anything that it has been in contact with before. The sequence of assembly does not have to be the same as that of disassembly. 

850 tuimelaaras 7

Nearly ready for use. Oiled and wrapped in a cotton cloth, it's in a plastic bag waiting for use. What I will have to do after installing it is checking if all the rockers touch the valve stems in the correct spot.