Wasting time constructively
SEAL 15 CC 4 CYLINDER ENGINE
Designed by Edgar T Westbury
This is my latest project and one that may take a while to complete. The Seal was designed in 1947 by Edgar T Westbury, as such it relies on technology of the period. Engines were usually side valve with two bearing cranks and of modest power output.
I have long been an admirer of Westbury's work. I plan to use methods as close to those employed 75 years ago when this engine first appeared.
Before committing to an expensive set of castings, I ordered the drawings which are accompanied by Westbury's construction notes published in the Model Engineer. The most challenging component appears to be the camshaft, which poses a number of problems; it is slender, is 5" long and ranges in diameter from 1/2" down to 1/8". Westbury suggests machining from mild steel then case hardening. Past experience suggests that preventing the part becoming banana shaped during the hardening process would be the greatest obstacle to overcome.
The photographs below show the process, including making the special turning fixture to create the cam lobes. Final profiling was done by hand, using radius gauges.
After hardening I was delighted to find that the camshaft is straight to within 0.003", Westbury designed in about 0.005" "wiggle room" to allow for distortion during the hardening process. The cam lift should be 5/64" (0.078") they all are within a few thousands of nominal which should be fine.
The whole process took way longer than I had imagined, that said if I need to make another I think this could be achieved in a couple of days, now that I have the turning fixture and the work flow sorted out.
CASTINGS
Having successfully made the camshaft I ordered a set of castings and associated material from Hemingway Kits. I carried out an inspection of the castings and was disappointed to find that they were not very accurate. The main problem was the block casting which was oversize on width and length. As this casting is cored for the cylinder liners and valve chest it caused a lot of head scratching to work out a way of getting everything to line up, while still retaining some of the cast surfaces. Eventually I managed to arrive at a compromise where everything would work. More about the castings later.....
MACHINING THE BLOCK
The images below show the machining of the main block and rear bearing housing. The dimensions are critical as there is very little space within. I had to remove material from within the casting to make room for the camshaft. As I mentioned previously the castings supplied are not good dimensionally. In the end all the bosses at each end had to be completely machined away.
CYLINDER LINERS
This engine uses "wet" liners, these were made from fine grained continuously cast iron. They were made to be a light press fit in the block. They will be honed later when I have made the pistons.
CRANKSHAFT
Westbury designed the Seal with a two bearing crankshaft; this was to simply the engine and make it more compact.
Machining the crankshaft, posed a number of challenges, the greatest of which is keeping it straight.
The gallery below shows the machining sequence, a paper patten was glued to the stock as a guide for material removal by chain drilling and some work with the hacksaw.
