Indian Four Motorcycle
Indian purchased the ownership of the name, rights, and production facilities of the Ace Motor Corporation in 1927.
Production was moved to Springfield and the motorcycle was marketed as the Indian Ace for one year.
In 1928, the Indian Ace was replaced by the Indian 401, a development of the Ace designed by Arthur O. Lemon, former Chief Engineer at Ace, who was employed by Indian when they bought Ace. The Ace's leading-link forks and central coil spring were replaced by Indian's trailing-link forks and quarter-elliptic leaf spring.
By 1929, the Indian 402 would have a stronger twin-downtube frame based on that of the 101 Scout and a sturdier five-bearing crankshaft than the Ace, which had a three-bearing crankshaft.
Despite the low demand for luxury motorcycles during the Depression, Indian not only continued production of the Four, but continued to develop the motorcycle. One of the less popular versions of the Four was the "upside down" engine on the 1936-37 models.
While earlier (and later) Fours had IOE (inlet over exhaust) cylinder heads with overhead inlet valves and side exhaust valves, the 1936-37 Indian Four had a unique EOI cylinder head, with the positions reversed. In theory, this would improve fuel vapourization.
In practice, it made the cylinder head, and the rider's inseam, very hot. Dual carburetors, fitted in 1937, did not help. The design was returned to the original configuration in 1938.
Like the Chief, the Four was given large, skirted fenders and plunger rear suspension in 1940. In 1941, the 18" wheels of previous models were replaced with 16" wheels with balloon tyres.
The Indian Four was discontinued in 1943
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