Jim,
If you are referring to the valve timing, there are timing marks on all the pinions. With the pistons at TDC, you should be able to align the marks. However, you will find the idler has an odd number of teeth, so the marks only line up now and again. The easiest way is to remove the outrigger plate and remesh the idler. You should end up with the valves just 'rocking' with the piston at TDC. (i.e. exhaust just closing as the inlet starts to open).
To time the magneto - bring the pistons to TDC and with a rod in the spark plug hole, check the depth to the piston and then add 7mm, then turn the engine backwards and then bring the pistons up again until they just contact the rod at the new mark. Check which cylinder has a valve open and time the mag for the other cylinder. On the Mark series engines, it is possible to remove and fit the mag complete with the timing gear, providing you remove the offside clamp stud to allow the mag to slide back. Also, remember that on these engines the crank and mag rotate anti clockwise looking from the back. The figure of 7mm before TDC is calculated from the 36 degrees quoted in the handbook printed in 1950, so, with the modern 'improvements???' in fuel technology, you may need to adjust the timing on the advance/retard to find the best setting.
Regards,
Eddie.
