Timing Calibration

The topic of timing calibration came up in Illf8ed's thread on jet sizes. I would like to see more on this topic, but had already attempted to hi-jack that thread with a different off topic question. I read some directions given by Norbsa in an old thread on calibration and looked at timing wheels to see what is available out there. Then of course I started wondering about how to attach a wheel to the end of the crank and see that the thread there appears to be 5/8 X 20 tpi. What the heck is that? I can't find it on any thread chart.

I also see that most of the wheels are solid discs but the Wassell tool has cut outs in it. I pressume this is to allow the user to see the rotor, but would like to know what others have found useful.

Here is the old thread:
timing-wheel-tool-use-t1258.html?hilit=calibrate timing

Any tips or information will be much appreciated.

Russ

I cut the centre out of a Wassel disc so that its a tight fit on over the rotor nut, works for me !

5/8 X 20 tpi is a cycle thread, on the larger sizes the cycle thread spec allows 20 tpi instead of 26 tpi as an option. Generally the 20 tpi is used in high torque situations where the thread form needs to be stronger, eg wheeel spindles etc.

I have both types of wheels. One for the crankshaft and the one I used yesterday is for the camshaft (1 degree of camshaft movement equals 2 degrees of crankshaft). The camshaft wheel scale compensates, so states crankshaft degrees. Wassel made these, however mine is a BSA tool. The camshaft wheel is handy as you can fit it to the end of the magnetic trigger or autoadvance unit and not disturb the primary cover and timing scale. I set TDC on the camshaft wheel then compared the reading to the scale in the primary. I got a perfect match, so confirmed the primary scale was accurate.