Hello Nick, I agree. The sets of castings I have purchased have been disappointing in finish especially. I did toy with making my own head including overhead cam when I got the first set but skill overcame ambition! However I am in the midst of designing my own engine which is a long term project. I was put onto Alibre and Its a great program. I have even used it to design before build recently to make some brackets, and it worked!
Today I managed a session in the workshop and completed (other than cutting a screwdriver slot in the valve faces) the first set of 8 valves. Last night I thought I would change my plan and get something to revolve to spur me on! To that end I ma going to get the valve side completed i.e. the camshaft fitted and working on one engine. To that end I drew up machining methods for the tappets, nuts, valve inserts, and camshaft bearings so that side of the engine works!
So after completing the valves the next items I was going to tackle was the two 1/4" hex nuts per valve. That was until I found I didn't have a suitable drill for the tapping. According to my charts I needed a 1.8mm No. 50 or 0.0709" drill. When going to my numbers drill box the only one missing is ............yep No. 50. So that job was put to one side and instead I decided to make the two camshaft bushes. The first went well enough and was reamed 0.250" and was pleased when it fits the camshaft nicely.
The second bush however produced another problem when checking the main block casting. This one was bought second and had some work done by the previous owner. All the work when checked previously was of a high standard, however the two holes bored previously were not the same. One, the timing end was spot on but the second was slightly oval! So worked stopped on the bush because it will need to be oversized, and the casting set up on my angle plate on the mill and the hole bored circular. When the finished 'round' hole was measured the bush will need to be some 35 thou oversize.
I can't see this will cause any problems yet, but will keep my fingers crossed. I will be using some hardening powder for both the nuts and the tappets, for the first time so that will be interesting. I have had it for a couple of years now and never used it before so if anyone has any tips additional to the 'normal' instructions I have, that would be very helpful.