I'll leave you to judge, I was in there at 6AM and did five hours!
I started the day by tidying up in the shed, first thing was to bring all the parts into the kitchen to clear the decks.
Then I cleaned and oiled the big surface plate, put a clean tablecloth on and got my ducks in a row.
Before you start on the castings you have to get your head straight and understand exactly what it is you want to do. Castings by their very nature are rough, not square and you aren't even sure the bore is on centre, cores have been known to move during the process of casting. What we are after this morning is the most accurate face we can get for the valves to run on, that face has to be parallel with the eventual bore, the ends of the cylinders faced off square to each other and the cylinder bored in the centre of the meat of the casting. Mick had already driven some good hardwood plugs into the bores and my first move after a good inspection of the casting for surprises was to mark the centre of the bore as near as I can get it. Note this isn't the centre of the core hole, it's the centre of the meat of the castings. No easy way to do this, lots of intelligent guesswork! Once you have a notional centre marked on each end of both cylinders you are ready for the next stage.
First I mounted the big vise on the VM table and squared it with the ball bearing trick. Remember that what I want is for the surface of the valve face to be parallel to the centre of the bore so a bit of careful setting up. The ends of the cylinders are rough and not square at this point so you haven't got a perfect hold. Do the best you can and when you judge you are as close as you can get, tighten everything up and start cutting carefully.
Some time later you finish up with these. Don't worry too much about finish because the face will have to be milled again once you have perfectly parallel ends on the cylinder. You have to start somewhere and this will be your register until you achieve something better.
The Gospel according to Newton says that what you need now is a big 4 jaw chuck and grab hold of the casting best you can. The main things you are after is the valve face being 90degrees to the chuck face and the casting centre is the pop mark you have made in the wood plug. Take your time, get it as close as possible and then machine the face until you have a clean finish across it. I used my wobbler to get it as good as I could. Then start cutting across the face.
A quick check with the square and it is almost a perfect right angle with the valve face. Reverse the casting in the chuck seating the good face on the chuck face, centre it again and cut this second face dead parallel with the first. Later you can set the cylinder in the milling machine using these two parallel faces as your new register and take a skim across the face which will then be a perfect right angle with the the faces and dead parallel with the bore.
You'll never have the cylinder more accurately set up than it is now so you might as well bore it. You can see that the core was almost dead centre. I carried on boring long enough to satisfy myself that it will have got rid of the hard inclusions in the bore well before it reaches the finished size of 1.5". Then I knocked off. Five hours is too long for an old fart like me but I had got to where I wanted to be on the first cylinder..... Go and do likewise!