1936 Spring announcement of 61E at bore and stroke of 3 5/16 x 3 1/2 = 60.3 cu. in. Cradle twin down-tube frame, heavier fork, horsepower is around 36 on 6.0:1 compression. A four-speed constant-mesh transmission (Indians were still shifted by crashing gear teeth into mesh sideways), multi-plate clutch, 565 pounds wet with one gallon of oil. Dry sump pumped lube system. A single four-lobe cam is used, requiring non-parallel unequal-length pushrods. Much of the detail design work came from Hank Syvertson and Joe Petrali. It was released over their objections in June, despite fairly severe oil leakage, chiefly from the rocker boxes. Much of the reason for this chronic leakage was the complex shape of the surfaces to be sealed, which was over-ambitious. When heads heat up and cool down, gaskets are subjected to expansion and contraction of the parts they seal, and this remains a difficult problem to this day. Rocker boxes were separate, bolted to the finned heads via four cast-on lugs (Andrew Wilgoos at Pratt &Whitney had patented cast-integral rocker boxes). The iron head was retained by five short fasteners, and had five horizontal fins. The front exhaust port turns 100-deg to face downward. Linkert float carburetor, used until 1965. Cylinders were base-bolted to the crankcase by four short bolts each.