I`ve been dreading building the valve block, the truth is, I didn`t really understand how it worked despite hours of reading plans and posts. However, thanks to Doug in the USA who wrote a very detailed explanation of how the parts work on the plans for me.
I really struggled to come to a decision on how to machine this. As far as I could see, the important factors were that the 3 blocks had to have perfectly flat surfaces to mate well (I expect paper gaskets will be used still) and that one of the long sides will be perfectly flat so that it will seal well with the cylinder head. I needed to convert the bolt holes to metric because I didn`t want to go searching for the imperial bolts. I changed them all to M3, but it was hard work as they were quite close to intercepting (even with the approximate 2.5mm bolts advised).
I wanted to use brass so I took one of my stock 1.5″ square bars and cut off 3 slithers. I then faced up the surfaces to thickness. I moved from the plans as another builder, Doug, advised, making the top and bottom block a little thicker to allow a better connection with the exhaust and intake.
So now do I work on each individually and hope they all square up at the end? No chance, I know my limitations and the only way I would get everything to locate would be to make it as one block. So I marked out the top block but allowed 1mm the close sides to machine back as well so in reality I didn`t have a datum face yet.
I then clamped, drilled through the top two blocks and tapped the bottom block, holding them all together.
I then spent a long time aligning the bolts with the new face that was to be cut, i.e getting the bolts parallel with the bed. I then squared up the rest of the block to size:
I then centre drilled (and will located off this hole when I took it apart to increase the hole dia of the two out blocks. I then horizontally drilled the two holes to bolt the block the head. This was near to colliding with the centre hole and the 4 holes holding the block together. I had concerns the drill would wander and intercept another hole ruining the block but I peck drilled slowly and all was fine! I then countersunk the holes for countersunk allen screws.
From the other side, the 0.188″ hole is drilled into the centre bore of the valve block which connects to the head.
I then took to block apart so that I could drill and counter drill the outside blocks to insert the valve guides.
And this is where I am currently at… an exploded photo showing the top valve guide fully inserted and the bottom valve guide about to be pushed into position.
One of the valve guides is a fantastic pressure fit, the other is just a “good” fit so I hope that the loctite I use will provide a good enough seal. I expect it will. So the next job is to loctite them in place once I`m happy everything is ok, let that set and then drill into the side of the blocks, through the guides for the exhaust and inlet holes. Before all that, I need to cut the valves and use some grinding paste to lap them to the valve guide seats.