I see by the pictures that this fellow made his own patterns and cast his block in two pieces much like I did except that mine was machined from a block of aluminum.
Over the years I had seen a couple of Holt models and thought it to be a very unique and attractive engine. In speaking to a couple of the fellows that built their engines I found out about some of the shortcomings of the design and castings. Having built some of my previous engines from bars stock I ordered the plans from Coles and built my own except for the large flywheel and manifolds, those I purchased from Coles.
As I remember from the drawings you are required to run a file through the windows of the crankcase and smooth out the bearing surfaces to accept the bearings. From the top of the crankcase you drill holes that go down to the bearing surface and provide a hole for the threaded holes that hold the bearings in place. With the bearings mounted the crankcase needs to be set up for line boring through all the bearings.
Attached are pictures of my setup. Although not identical to what the cast block would be the principle is the same. A long boring bar needs to be fabricated, in my case I made a bar with multiple cutters so that I didn't have to travel the lathe carriage as far. For the cast block a bar would be made with one cutter. The crankcase was mounted to a plate on the cross feed of the lathe (compound removed) It was indicated square and then clamped tight.
The boring bar is inserted into the block and mounted in the headstock and supported by a live center on the other end. The cutter is adjusted by miking over the cutter and bar then subtracting the diameter of the bar to obtain the offset.
This is line boring. I can think of no other way to accomplish this job because if you tried to drill and ream through the bearings the tools would wander all over the place and you would get a very crooked hole.
gbritnell
