Can anyone confrim the position of the valve gear timing mark on the OS 81a. The generic advice for OS four strokes is the timing mark to be at the 12 o clock position ( vertically aligned with the bottom of the valve stems?) with crank shaft at top dead centre. Just to confirm the above would be helpful.

Many thanks Bob Vaughan

The "generic" advice is wrong. Here's the correct way:

(photo courtesy of Minnflyer)

Thanks Bill..............much better.<div>
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</div><div>Bob V</div>