The cylinders eventually arrived and quite a lump they are too. As can be seen in the
picture, the portways are cast in. A lovely saving in work time apart from the fact that
the accuracy of the portways is not very good. In theory they should only need cleaning up.
In practice the solid wall between the inlet and exhaust on one side is less than the
drawing dimensions. When I faced off in the mill I found the land was 50 thou under size.
There being no alternative but to return the block for a replacement. I drove the 110
miles for the replacement and getting it home, skimmed the surface to find that this time
the results were even worse, as can be seen in the picture. 
On talking to the suppliers I was told that the batch was being returned to the foundry with a criptic note! I decided that I would find an alternative solution to waiting months for another casting. It's a pity that the accuracy can't be spotted until the surface has been machined. Just about everything is wrong this time; land size, position and portway. I've only done one block but I've no doubt the second one will be the same. I'm thinking the solution is to mill off about another 1/8" and make up a plate with accurately made portways and clamp this between the block and the steam chest.
I bored the cylinder on the lathe
using my largest boring bar, but even this still gave me chatter problems. I'm hoping that
the hone will be enough to remove them. The quality of the cast iron is not wonderful but
as somebody pointed out; the little holes hold the oil!!
Back to the mill to face off the supporting brackets. I needed to be able to calculate how
much to take off and I could only do this accurately after I'd found the cylinder centre.
Clamping wasn't too bad for cutting the two rear supporting mounts. The photo shows the
way I did it. Small cuts and the vibration was within limits. While in this position, I
cleaned up the middle area and changed the top clamp to the other side before finishing
the surface.
At this stage it became obvious that the original drawing which showed bolts of 3/8" diameter, were going to be too big. There just wasn't enough width in the brackets after they'd been cleaned up. The problem was that the frame holes had already been drilled. There was nothing for it but to strip everything off to get back to the frame, and then fill the holes. The first job was to locate where the new holes were going to be. I settled on 8mm bolts and four each side.
Back to the computer to print out the new arrangement full size
I stuck this to a piece of 1/8 sheet. All the holes had been marked with centres so I drilled
out two of the 3/8 holes full size and drilled the new holes with a 4mm bit. This template
was bolted to the frames and it was possible to drill at least two 4mm holes in the frame
without fouling the larger holes. Next, I gave the 3/8 holes a deep countersink, then plugged
them with 3/8 steel rod. I had to drive them in as they were a tight fit. I then MIG welded
in the countersink and finally levelled off with an angle grinder and flap wheel. It made
a mess of the paintwork which meant rubbing down and repainting. I now bolted the template to
the frame using the two 4mm holes and drilled out the remaining six. I removed the template
and redrilled 8mm. Owing to the accuracy of the CAD and the digital readout on the mill,
the bolts were a perfect line up. The picture on the right shows that the exhaust port holes
were also drilled and tapped.
Next came the steam chest. Not too much of a problem and
the casting seemed to be OK, which is more than can be said for the endcaps!
I think this is about the worst casting I've come across. In the first casting I managed to
turn the pit out but in doing so, I lost the centre boss, which is really only of aesthetic
value. However, the other one was almost done with the reverse side finished; so I wasted
several hours. I'll pick up a replacement at the Donnington exhibition. One thing; on my
next engine I'll go back to making my own patterns with a foundry I know produces good
results.
