Continued from Part three here.

The cylinder head was the next logical casting to get out of the way. After a quick clean up I made a start by holding it in the 4-jaw slipping a parallel under each of the stud bosses in turn to make sure the outer cast surface was reasonably true across the lathe's axis and than machined the underside of the head so I had a good flat surface to work with. I also took the smallest of cuts off the OD to get the head round but not far enough up the sides to remove the draft angle.

Next the head was clamped to the mill table on a piece of MDF. I held a straight edge against the two valve bosses and eyed that up along the X-axis so the valves would sit horizontally. Then the three ends of the T where milled flat, the inlet and exhaust ones just want the minimum taking off so you get as much thread depth as possible for the pipes but the one for the rocker bracket should be machined to dimension. The clamps will need moving about to allow access to all three faces. The tops of the valve bosses can also be leveled off at this stage.

The bosses for the four head studs are not equally spaced around the head so I spend a bit of time getting the best centre for each boss and noting the DRO readings before spot facing and drilling 4mm. Ignore the fact they are tapped in the photo, I was going to hold the head one way for the next op but did it another.

I like to do the valve guide, valve cavity and valve seat on the lathe rather than use  a CSK bit in the mill which can chatter and I've not yet had to make a valve seat cutting tool for any of my engines doing the seats with the topslide set over. So I made some simple standoffs from tube and screwed the head to a scrap piece of square aluminium plate which could then be held in the 4-jaw to position each valve hole in turn.

The square piece of plate also made it easy to index the head around to drill and tap the inlet and exhaust connections. The M3 tapped hole for the rocker could also be done at this stage though I did mine later as I wanted to tweak the rocker post casting to suit having the exhaust valve on the far side.

Still holding you the plate the spark plug hole was drilled, spot faced and then tapped M10 x 1 for a CM-6 plug.

When I did get round to doing the holes for the rocker post this is how I set it up to do the tapped hole using two drill bit sin the valve holes to set the work vertical and then using the side of a drill bit to run the edge finder against.

The two drill bits were used again for the 3mm clearance hole being pressed against a table tee slot to line up the head and run the edge finder against then the hole was drilled and the opposite side countersunk.

lastly the carefully noted stud hole positions can be used to locate the holes in the cylinder so they can be drilled and tapped making sure not to go too deep and break into the water space. You could spot the positions from the head but I seldom use that method since fitting the DRO.