A heavily-disguised prototype has been seen on test, looking a lot like a current Chieftain but with an upside-down fork and Brembo brakes. However the real clues have been revealed in a patent from Indian that focuses on its cylinder head and valve train.

Appearing to be around the same size as the existing air-cooled Thunder Stroke 111 (1811cc with pushrod-operated valve gear), the new engine features a single overhead cam in each cylinder head with a huge radiator.

Patent diagrams show each cylinder’s single overhead cam operates four valves, with the camshaft sitting deep in the head between the intake and exhaust valves and acting on roller-rockers. This means the top end is nearly as compact as a pushrod engine’s cylinder head, and is far less bulky than the DOHC design used on Indian’s current water-cooled 1100cc engine.

By Ben Purvis