Ransomes Marquis 4A 20” Rear Roller Sprocket Removal Disaster.

Hello,
I recently had a Marquis 4A given to me , it sadly having been left uncovered in a leaky shed for 8 years .
After a carburettor clean up and new points ,plug and coil the engine is running fine .

The rear rollers are seized solid so I made up the locking tool and chain wrench as shown by Wristpin , which worked really well , but the sprocket is so tight that pulling steadily ( left hand thread) on a long lever produced a nasty snapping noise which was one half of the slot on the end of the roller shaft cracking off .

Any suggestions as to where I might go from here in terms of stripping out the rollers and finding a replacement roller shaft ? The only knowledge I have about this mower has come from this club forum , and I’m very pleased I joined. The very detailed posts have been great. I’m normally tinkering about with my two old Triumph 650’s, so slightly out of my comfort zone with this .

Any help would be gratefully received .

Thank you .