Benelux mid-50's derailleur - not adding tension - any ideas?

[DCLane]

I've been working on the Carlton I picked up from @jfk262 last November and am almost done. However, I've hit one final snag which I can't resolve. The rear derailleur doesn't appear to add tension and, as a result, the chain slips quite a lot and I can only get three of the five gears.

It's a 1955 Carlton running Benelux gearing, I'm unsure of which type but it appears to be 1949-1953 Cyclo Benelux. To say I'm unfamiliar with these would be an understatement. It's been removed, after being coated in gunk, rust and grease for many years, cleaned and re-greased before re-fitting with a new cable outer and inner.

The bike originally as picked up and derailleur looked like this:




Progress has been made, with the Carlton now looking a bit tidier:



However, the rear derailleur just doesn't shift properly. Current photo of it:



Any suggestions would be gratefully appreciated.

 

[bikeworkshop]

Does the cage need a full counterclockwise rotation (to tighten the spring), or am I confusing dérailleurs?

 

[jim haseltine]

That's a Benelux Mark 12. My first thought is that the chain is too short by something like 4 double links but full fitting instructions are here - take note of the 'three rivets' comment in paragraph two on page 3 of the scan.

 

[DCLane]

Thanks @jim haseltine - I'll have a good read of the instructions. Also, identification of the derailleur is appreciated.

The chain is the same length as the one which was removed prior to re-spraying, so shouldn't be too short. However, I can't guarantee it worked before.