[ndutton]

In 1947 the Atomic Four was introduced. It was a 4 cylinder inline / 1 litre (64.46 cu. in.) / 30 hp engine, Model UJ - 5101 (direct drive) / UJR - 5102 (2:1 reduction gear) / UJVD - 5103 (V drive, 1:1, 1.29:1, 1.67:1, 2:1 reduction gear options) L head (flat head) engine incorporating an integral reverse gear, with roots stretching back to the earliest Universal 4 cylinder engines. It was not a modified Jeep or Farmall tractor engine (the early military and civilian Jeep engine was a 4 cylinder, L head design like the Atomic Four, but it was twice the size of the Atomic Four at 2.2 litres (134 cu. in.) and had 3 main bearings - the Atomic Four has 2. In 1953 Jeep switched to an F head engine) and if anything was based on the successful Utility Four life boat engine. Sales of the Atomic Four grew strongly after 1955 as the recreational sailboat market expanded.

To add to Tenders post, as far as I know the industrial engines that were marinized (Palmer, Gray Marine) had center main bearings. The Atomic 4 does not, never did. However, I can cite a single instance I know of where an Atomic 4 was used in an industrial application. At Islander Yachts one of our forklifts needed a heart transplant and we had maybe 20 A-4's on the shop floor. Our maintenance mechanic/tool repair guy was quite a craftsman and very resourceful so in about a week there was one less A-4 on the shop floor and a forklift back in service.