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- Jun 30, 2012
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In Triumph motors E3134 race cams are usually run with R type cam followers. The normal followers have less radius which give a slower lift rate. In a Commando motor, the cam is almost as hot in timings as an E3134 and the followers are flat, so give the quickest lift rate. The tappet is the screw and lock nut at the end of the rocker arm with adjusts the valve clearance. Less clearance gives slightly longer timings. I think the cam in my 850 motor is probably a 650SS grind, which is sufficient. If you read Tuning for Speed, the valve timings are listed in there for most of the 1950s race bikes. A 1959 AJS 7R was the best of the 350 singles in the 1950s - so the timings for that might be relevant. The timngs and exhaust system set where the power band occurs. A quicker lift rate can give more power, but the cam can beome a valve-dropper, depending on the weight of the valves and rocker gear you are using. My 500cc Triumph engine was capable of revving to 10,500 RPM safely. My 850 engine revs to 7000 RPM. I have not lightened the valve gear in the 850 - there is no need. With the relatively mild cam, valve float does not occur.
If you are using a more radical cam, Jim Scmidts followers would be a good way to go. But the 850 motor is fast enough, if the crank is rebalanced to suit revving to 7000 RPM.
I never believed in my 850 motor - I now love it. The gearbox is more important than a hot cam. A hot cam with a wide ratio gearbox can slow you down. A more pronounced power band must be managed better. With a Commando motor, the corners are more important than the straights. You only need to be fast enough to keep-up with the lead bunch on the straights. It does not matter who gets to the next corner first. Most other race bikes will be slower in corners. On race circuits, at least 40 % is usually done with your bike on a lean. in corners, you need less lean and more torque.
If you are using a more radical cam, Jim Scmidts followers would be a good way to go. But the 850 motor is fast enough, if the crank is rebalanced to suit revving to 7000 RPM.
I never believed in my 850 motor - I now love it. The gearbox is more important than a hot cam. A hot cam with a wide ratio gearbox can slow you down. A more pronounced power band must be managed better. With a Commando motor, the corners are more important than the straights. You only need to be fast enough to keep-up with the lead bunch on the straights. It does not matter who gets to the next corner first. Most other race bikes will be slower in corners. On race circuits, at least 40 % is usually done with your bike on a lean. in corners, you need less lean and more torque.
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