A short video to show the working of the valve gear when the crankpin has been rotated by one 'notch' in the crankpin's spline. Simply put, I eased out the crankpin, rotated it a fraction, and reinserted it. The end of the pin is no longer above the centre of the wheel so the movement of the valve mechanism is exaggerated. Care has to be taken to ensure that the mechanism does not become too tight - the piston is travelling backwards as the crankpin is moving forward - so the combined effect is to pull the gear in both directions at the same time. The mechanism can cope with the pin being inserted one notch out - but it is up to you to check that the wheels revolve freely.

In fact, the adjustment is too much to be absolutely realistic - and it is possible to get it the wrong way - the valve should move forward just before the piston reaches its most forward position.