Coupling rod drive question

[vtsteam]

I'm considering changing my planned valve action on the 4 cycle to steam conversion project from semi-rotary (oscillating) valves to full rotary valves. The intended driver is an eccentric on the crankshaft.

A bellcrank on the valve itself would be easy to drive with an eccentric when using oscillating valve.

But to consider a full rotary valve, a coupling rod and a crank disc and crankpin on the valve would seem to work, except that I'm worried that at top or bottom dead center the valve may tend to start in the wrong direction -- under some special starting circumstances.

Is this a real concern, or will it sort itself out in a revolution? Or is it not even a concern at all? \

Or if it is a concern is there a simple classical mechanical solution?

Apologies for a possibly dumb question, I need to look to another set of grey cells, I've been going around in circles on it.

I did think about the drive of an 0-4-0 locomotive -- but realized the track itself enforced one way revolution for both driven wheels.

Thanks in advance!!!

ps I know I could do it in other ways, timing belt and pulleys or chain and sprocket, or even train of gears, but the eccentric appeals to me. Also I want to make all of the parts myself, and timing belts and chains are not items I want to fabricate!

[vtsteam]

Probably too wordy above. The problem is one of two coupled wheels. And the answer seems to be that yes, they can get out of directional synchronization at the dead centers.

Solutions shown in "1800 Mechanical Movements Devices and Appliances" by G. Hiscox are dual coupling rods set 90 degrees apart, or a third wheel on a single rod, either inline (like an 0-6-0 loco) or  out of line with a rigid triangular coupling rod.