Norton Twin, Oversize Cam Followers: Anyone know of a supplier?

Britstuff said:

Hi Jim:

I was hoping you would chip in at some point. I certainly get what you are saying about radiused cam follower ends and broader camshaft profiles being superior. If I was smart I would have installed your modified BSA lifters and cam shaft when I had the motor apart. However, I did not. This motor runs your lightweight pistons and rods, my Commando runs a set of your pistons. Both are excellent!

While clearly not the optimum configuration, can you confirm whether your BSA lifter setup can or cannot work with a non JS camshaft? Naturally part of the answer depends on how broad the camshaft lobes are. I believe mine are a bit wider than standard, my cam is supposedly a longer lasting type I purchased from Norvil, that I think has wider lobes, (maybe not as wide as yours). One useful clue may be the wear pattern on my existing cam follower pads. Somebody apparently radiused them, the wear patterns seem to suggest the width of the contact marks.

Truth be told. I would prefer to use your BSA lifters. Lighter, probably a lot quieter, I don't even need the help of a machine shop to install them, (although getting the height right clearly takes some thought).

Thank you!

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jseng1 said:

You have only the slightest radius on your stock lifters shown in the photo above (post #19) and that may be alright but generally when you combine a cam that was designed for flat lifters and change to radiused lifters you suffer a significant loss of performance because you are reducing the duration.

If you use a higher performance flat lifter cam with radiused lifters you get some performance back but your duration is still reduced. This means that because the performance cam has the increased lift the valve has less time to reach and decend from that lift - the velocity/speed of the valve can be too much for the valve spring and the valve/lifter will "float" at high RPM by losing contact with the cam and reach even higher lift than it was designed for - again tangling the intake and exhaust valves resulting in destruction. This problem holds true (but to a lesser extent) with lower lift cams such as stock cams.

If you look at it the other way around - combining flat lifters with a cam that was designed for radiused lifters will increase the duration so much that the intake and exhaust valves will again tangle with each other and destroy everything.

Generally speaking its a very bad idea to mix radiused lifters with flat lifter cams or visa versa. You can put a slight radius on lifters designed for a flat lifter cam but that's about it and you'll need good strong springs to inhibit valve float. Either that or keep the RPM down low which is no fun.

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