This weekend I've been making a lot of swarf! With the help of my mate Ralph, I've been working on a revised crank shaft trigger wheel. The standard setup clamps a solid wheel to the front of the pulley with a spacer washer underneath it to pack out the space created by the dishing of the pulley. The drawbacks of this arrangement are weight, poor centration and poor repeatabiity on angular location.

I measured the weight of the pulley, trigger disk and spacer washer at 1010 g. My revised arrangement uses an alloy spacer ring block with a 75mm OD and 54mm ID. The pulley was machined with a well with a 75mm ID to center the ring in the pulley and the centre of the trigger wheel was removed. A shallow well was turned into the back of the trigger disk, again with a 75 mm diameter, so that the disk, pulley and spacer are all tightly co-aligned. Having removed the centre of the trigger disk, I needed a replacement washer for the bolt to clamp down on, which I made from the centre of the spacer disk.

The new set of bits now weighs 748 g, a 26% saving.