Sounds like a coupling commonly used on machinery to allow for small amounts of misalignment. The chain should have a joiner link on it that can be undone.

John

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JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol

Thanks for prompt reply. You are quite right. The drive shaft from the engine/Tx PTO enters the coupling at a slight angle to the winch drive shaft on the other side. On the engine side there is a copper shear pin - on the winch side the shaft is keyed to the coupling. It is not clear to me that I need undo either of the two circumferential chains (but I could be wrong). If I unbolt the winch and pull I think the winch drive shaft might just slide out of the coupling. (I'm not going to try that right now, as I'm going away in a few days for a week, might need the winch and everything is working right now - the other maintenance job can wait. I don't need to create a new problem for myself until I have time to pick up the pieces!) Does this particular type of coupling have a name - I would like to know just how it works and what the function of the two chains is? Well, I guess they transmit torque across the coupling in some way - maybe if I cleaned it I could see better!
Carl

I don't know of a specific name, but it is the same topologically as the gear coupling - see . The two chains are in fact a double row chain - one half of the chain is driven by one sprocket, the other half drives the other sprocket.

John

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JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol

You are right again - I realized that when I looked at it again this morning - it is indeed one double row chain over two sprockets. I presume the give in the chain takes care of the misalignment of the drive shafts. That's about all I need to know about it. I should be able to remove the winch either by undoing the chain or by pulling the keyed winch drive shaft free of the coupling. I guess undoing the chain would be the pro way.
Carl