Seized Up Windmill

Sometimes, with enough strength, you can lift the impression lever enough that it will release the platen. I know you can also self-rotate the flywheel backwards to release the impression but I haven’t done it myself.

Once the press is off impression, the press usually can be advanced.

If the impression lever cannot be turned-down to the point of release, there is an anti-reverse disk near the flywheel that can be lifted and the press can be turned backwards just until the impression lever can be released. Do not turn backwards any further, or the press can be badly damaged.

Only proceed with the motor power off.

Refer to p109 in the manual “Backing up the press”.

In essence, the Thompson British Auto Platen, in many respects has virtually the same system as the H/Berg as regards the SHEAR Collar safety device, is almost identical to the Thompson???
As your machine is still jammed hard on impression the shear collar has probably not yet sheared (broken), if it had you would almost certainly be able to turn the machine over with NO resistance & No impression whatsoever!!!
Therefor initial suggestion would be thus:- Slacken progressively the FIVE (5) 28/32 m/m Approx. bolts on the Shear collar device just a few turns (orogressively) which should release the impression, rotate the machine normal way to remove all/any obstruction(s), with the Platen open re-tighten the 5 bolts, H/Bergs as with Thompson,s generally, not considered advisable to turn backwards.!

Unfortunately the Shear collar is situate at the Base & The rear of the Machine, i.e. Hands and knees and a kneeling cushion.!! . .Info based on Thompson, U.K. only.!
Good luck

I got it!! Thank goodness. Thank you for all of your help.

I was able to muscle the flywheel forward enough so that we could get off impression.

Now, am I ok to print? Or might the shear collar have been broken?

If the collar has fractured, the impression settings typically used prior will seem too light.