That type of ratchet end is commonly found on orthopaedic bone clamps but here the tool is apparently used for extension instead of compression. What is odd is the angle of the jaws. In bone clamps such jaws widen the area of compression and still perhaps allow fixator access. Here they don’t look angled to grip during extension, suggesting that some specially shaped items that fit into the jaw notches?

pgk

I should really have said Valve Spring Lifter, rather than compressor.
I haven’t found one quite the same yet, but from the 1922 Sears Roebuck catalogue

1927 Auto Supply Company

Getting closer, but not quite
BOG Catalog No 8

Bill

Only thing that suggests possibly not spring compressors is that the outside faces are curved / tapered toward the edge. This means they would be forced out of the gap. I’d expect them to flat, have a recess or even be tapered the other way.

Robert.

Absolutely of the type suitable for my Model A Ford. Might be a bit big for a small british side valve.

Frm memory, this is the sort of tool that would be used to release the valve, on a prewar Austin 10 and others..

The lower spring “cap” had a recess which covered a pin through the valve stem, so that the valve spring was retained by this “cap” washer.

Using this tool, the spring would be compressed allowing access to the pin. The pin would be removed, allowing the valve to be withdrawn for facing or replacement.

Howard