Replace Norton Commando 850 Clutch Plates


| 7/1/2017 12:00:00 AM


Tags: July/August 2017, How-To, Norton,

If you’re actually riding your old Norton Commando 850 — and we hope you are, because they’re one of the great bikes of the ’70s — chances are good that at some point you’ll have to replace the clutch plates. The original setup used five alternating bronze friction plates keyed to the center clutch hub, with four plain steel plates keyed to the outer clutch drum followed by a pressure plate and a single diaphragm-spring plate compressing the plates. It’s a fine setup, but eventually the plates wear. Slippage and overheating take a toll, as well: Once the steel plates start to blue, they’re toast, and both the steel and the bronze plates can warp from overheating.

The good news is, replacement clutch plates are readily available and the design of the Norton clutch makes servicing quite simple. Only one special tool, a diaphragm spring compressor, is required. You can buy the tool for $26 from donelsoncycles.com, or you can make your own if you want (go here to see how).

There are a few points to appreciate, one of them being the stacked height of the clutch plates. According to various sources, Commando 850 clutch plates should have a stacked height — the total thickness of all the plates stacked together — of approximately 1.17 inches. However, replacement clutch plates (even stock Norton items) rarely stack out to that exact specification. The height matters because of the nature of the diaphragm spring clamping the plates together. A shorter stack allows the spring plate to push farther into the clutch hub, resulting in a stronger pull at the clutch lever, while a taller stack means the spring plate is flatter, resulting in a lighter pull. That makes a taller stack desirable, but only to a point. If the stack is too tall the clamping pressure is reduced, increasing the risk of clutch slip. Back in the day, variations in stack height were routinely balanced by inserting a fifth steel “shim” plate to compensate, but shim plates are now hard to find.

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