aka "Shaky Jake"
The Jacobs Engine Company began in Camden, New Jersey, in 1930 with a 55-hp F-head three and a 150-hp seven. The 3-cylinder engine had a short production life, but the seven founded a long-lived line. Its output rose to 170 hp in 1931, and, enlarged as the LA-2 model, to 195 hp in 1932. The LA series Jacobs used exposed z-type rocker arms; they were the only U.S. engines to employ this dubious design feature. This was eliminated in the 1934 L-4, which used enclosed fore-and-aft rocker arms of classic design. The L-4 developed 225 hp from 757 cu in. (12.4 L). The 285-hp L-5 was added 2 years later. At 831 cu in. (13.6L) the L-5 was the largest American seven until the post-war Cyclone Seven was built, and it is easy to understand why its World War II nickname was the "Shaky Jake."|
In the market as in design, the Jacobs was a late bloomer. While used to some extent during the late thirties — the Beech Staggerwing (38.7 KB image) and the very advanced Spartan Executive were Jacobs-powered — it did not come into its own until the Second World War. Cessna used two in the "Bamboo Bomber" UC-78 and evidently became a convert to Jacobs power, since those exemplary airplanes, the Cessna 190 and 195, were Jacobs-powered (the 190 was actually Continental powered - ed.). One peculiarity showed up in the Cessna installations. The Jakes used coil ignition instead of magneto, and the distributor caps were prone to cracking. When this happens, the spark travels to the wrong cylinders and the engine runs rough. The cure was to have the cap undergo a bakeout in a vacuum oven and them impregnate the crack with insulating varnish, after which it would run forever without giving further trouble. The only difficulty was that this was illegal. What the government wanted you to do was replace the cracked cap with a new crack-prone cap.
Source: A History of Aircraft Piston Engines by Herschel Smith
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