....alternatively supply a picture.
Hi @lwik@bambuko - could you show the differential bolt (the rear spindle extension) out of the head. I assume it's an expanding arbor than locks into the spindle?
BTW, your head looks lovely. Better looked after than mine
Thank you for all the comments an photos - most helpful.... @bambuko, could you measure the length of your plug for me - I'm suspecting the inner plug was the original, and its just under 9mm long (but not threaded, as the new one will be!).
Agree, this is the only logical explanation, hence dog end grub screw, to lock the hole once you are done.I also suspect that the grubscrew (which the head above doesn't have) is simply a vent to allow air to escape as fluid is added. The heads with the larger piston (which from the brochure looks like how the new ones are done) don't need this.
It should always rotate, because there is no way to disengage this, but should rotate with the indexing disc, not with the indexing handle (if that makes sense?). Have you had that side housing off (pretty trivial to get off). There is just a simple bevel gear connecting the differential shaft to the outer shaft that mounts the indexing disc (the inner shaft connects through to the worm that drives the spindle). Yours has a different index disc lock than mine (mine has a ring around the disc, I think yours just had a pin lock at the top). If you release this, does it free up?
Yes, you are right again - just edited my last message.I had forgotten the head in the earlier picture wasn't actually yours! Your disc clamp is exactly like mine - the black ring around the disc.
Are you referring to the two grub screws in the middle of the disc. They should just be for jacking the disc off, and with the three black screws still in place shouldn't do anything? The lock I was referring to was the clamp bolt for the ring, just to the right of the oiler in the differential shaft in your picture. This should allow the disc to turn with your differential shaft