The Forum moderator has asked for updates on members' activities so I thought I'd add something for what it's worth.
I've converted a troybilt trimmer engine to water-cooled. It will go into another 65" mahogany boat (see prior posts). The water pump is an internal gear pump made from a honda oil pump. See photos below.
The attached drawings are designs I've been working on recently. I don't have the machinery to build them unfortunately. The vee four has a displacement of 200cc. The flat head is 100cc. The vee design could also be a twin and the flat head could be a four I suppose.The pump for the vee four is a dual-chamber gear pump of my own design.
My next project will be a design of an in-line four at a size I think I can construct. It will have a displacement of about 100cc's.
Below is a link to a video of the converted engine running. I think the ignition system is interfering with my cameras's electronics and that is why the distortion is present. I worry now that, without shielding, an R/C system won't be reliable.