April 2000 Racer Corner

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The 4-Cam System.

By Jim Wall

During Indians last fling a small batch of 4 cam big base racing Scout where put together by Dick Gross and ridden to success by Bobby Hill. The 4 cam machines where a system that included the whole machine.

The chassis was based on the 648 style factory racer but was retubed with thin wall chromemolly tubing and further lightened by drilling holes in various locations and plugging the holes with aluminum slugs. Aluminum fork links as well as motor plates where used. Gross painted everything on his machines to disguise what he had done. The handlebars risers where from the vertical Scouts and mounted with an aluminum plate to the fork crown.

Light weight machine oil was used in the hubs to cut rolling resistance as well as 10 weight oil in the primary and transmission. The front wheel was a simple hub and the rear wheel carried a sprocket to keep weight down. In talking with the son of the Indian dealer here in Denver he says he can recall seeing Hill at a race in Kansas. He recalls Bobby spinning the rear wheel as the machine was on a stand and that he and his father could not believe how long the wheel kept spinning on its own. The tanks where the factory narrowed 648 tanks, and the machine used a tachometer driven off the front cam, the tach was from a Norton. The saddle was from a Harley KR.

The motor was unique in that it still had the two camshafts, but each shaft had two cam lobes, one for the intake valve and one for the exhaust. This required a thicker cam cover in order to accommodate the extra cam gear. It also required a different exhaust valve lift, lift shafts, cam shaft shafts and pinion gear arrangement.

The set up essential used a factory cam to which Grosses own unique cam lobe was pinned. I've seen one set up where he was using a factory Savannah came run backwards with his own lobe pinned to it. He used a factory Bonneville lift with a spacer brazed to the side of it at one point. He also hand made his own lifts with different center to center lengths.

The cases where big base with ball bearings everywhere, and with a steel sleeve pressed in to the drive side to carry the ball bearings. He also
machined steel cups and pressed them in to the cases to carry the ball bearings for the camshafts.

The cylinders used a 1/8 over sized inlet nipple brazed in to the cylinder. They also had a 1/8 over intake valve. The exhaust valve was the standard size. They used the m-53 1 1/2 HD carb with the bombsight venturi.

Ignition was by magneto. The oil delivery to the motor was adjusted by pressing a drilled orifice in to the back of the aluminum oil pump directly in front of the pinion shaft. Different sized holes where used. All in all it must have worked well as they sure did run.

Lyle has cast up some of the deeper covers for use with the aluminum pump. They have to be machined. I have bits and pieces of one of the 4 cam motors, cases, oil pumps, one half of two different cam set. The missing bits, outside of the valve lifts, will be easy to do. At that point there will be a four cammer running again in addition to the two that already are.