1969 Bonnie

recently bought the bonnie , real problem with primary chain too tight but unable to loosen adjuster . grateful for any ideas

 

after removing the cover , I tried several screwdrivers into the adjuster but could'nt engage with any slot . Out of curio, I inserted an imperial allen key which seemed to engage with a slot and spent half an hour turning and turning the key but nowt happened. I know its supposed to be adjusted with a small driver , but nothing works. My next move is to take the cover back off and see how the adjuster is fixed onto the bottom of the inner case. I have trawled ebay and found a complete adjuster in the states , but I need to investigate further before I buy a replacement

 

thanks for replies , I will remove outer case again and investigate further . I am wondering if the actual adjuster part is actually in place , or removed or broken by previous owner , will let you know
Bob