I then turned, bored and reamed the valve chest (sorry, no pics of this) and cut the two recessed passages where the ports were to go, using a parting of tool. Then the ports were drilled and filed all the way through. Accuracy is very important here. The valve chest is to be a light press fit into the cylinder - the end parts of the valve chest stick out of the cylinder, and their o.d. is not critical to the thou. So I turned this part down until it would just pass into its bore in the main casting - then withdrew the tool by a thou (diameter) and cut a bit more. I tried it against the cylinder casting, and checked that it wouldn't enter the bore. I actually went over the surface with some very fine abrasive nylon (like panscrubs) to keep the interference fit to a minimum. The problem is that there is very little metal at the valve area, and it can easily collapse if the press fit is too great. (I've heard it suggested that a sliding fit and loctite might be better - as ret...