As a machinist I thought it was a neat idea to be able to build my own version of an inline twin
In 1976 I was reading an issue of Model Airplane news where I came across an article about a machined inline Twin engine.
As a machinist, I thought it was a neat idea to be able to build a marine version of an inline twin. I am a retired journeyman machinist and back then I worked as an experimental machinist for Varian Associates. I worked with the engineers machining parts for them to test on new machines that they wanted to build or modify. I had a machine shop all to myself so when I was not working with the engineers I would design and machine my own boat hardware just to keep from getting bored.
With full access to a Bridgeport milling machine and Hardlinge Lathe, I machined rudders, struts, motor mounts and even tuned pipes and crank rods. I found myself with more time on my hands in between work projects so I decided to tackle an inline .46 marine engine in my spare time. I built it for show using an OS Max .46 piston and liner along with crank rod, flywheel carb and front crankshaft. Once I had it assembled I tested it on the bench and it showed considerable promise. Afte the success of the .46 I decided to take it one step further. Next I built and inline Twin .65 using an OS Max 65 piston, sleeve, fly wheel, 7DV carburetor, and front crank shaft. I machined an air cooled block with water cooled heads. What a beast this turned out to be. It took me about a year to complete it only working on it a few hours a day or week. It wasn’t difficult for me at all. Iit just took time to do. With the induction timing correctly adjusted each valve is timed to open at 35 degrees after bottom dead center and close at 70 degrees after top dead center. This engine was only tested on the bench as well but it did run steady and strong. It was quite satisfying to see something I built partially from scratch actually work. I suppose that is part of the satisfaction of the hobby.
In hindsight if I were to do something different I would have the housing sand casted instead of machining the housing from three aluminum blocks where I had to hold it together with pins to line everything up. I think that would have been a better way to go.
Maybe one of these days I’ll fit it into a boat to see what it can really do but until then it’ll just sit on my work bench looking pretty.