A relative got locked out of a rental house (out of state landlord) due to a balky mortise lock in a decorative metal frame outer door. He called a locksmith to get him back in and the locksmith installed a used but "working" mortise lock which was still unreliable. I was over at his house and was asked to and agreed to "look" at it. At this point I am profoundly regretful that I became involved, but at the least must restore the lock to what it was when I unwisely began working on it.

I had never installed or replaced a mortise lock and blundered. I unscrewed the outer deadbolt cylinder and couldn't get it back in. I think the threads on the lock body and the deadbolt may be damaged. In trying to back out the outer deadbolt which I had cross-threaded trying to get it back in, I broke off an aluminum key in the cylinder. Right now the door works from the inside, but has the deadbolt missing from the outside.

My immediate question is can I remove the broken off part of key from the cylinder or is that part ruined? (I have access to the back side.) If I can get a new deadbolt, how does one screw it in while getting the actuating tab that operates the deadbolt in the right place to function? Is there a tool like a thin wrench that allows threading in the deadbolt actuator while holding the key to keep the tab in place?


I retrieved the lock from my relative's residence and in the peace of my own home analyzed the problem and located the right tool in my 50-year-old miscellaneous box. I poked out the broken off key with 2 or 3 23-gauge pins fused together. With the key in the right position the key came out smoothly.

I even think I see how to reinstall the deadbolt actuator. It is easy to cross-thread, however. It is a 1 1/8" cylinder being threaded into a narrow set of threads in the lock body.

The lock that was removed by the locksmith is a "Marks mortise lock model/function 90A right hand reverse". I assume the one in the door which was removed by the locksmith was same or the equivalent. I would bet that there was nothing wrong with the original lock (the one I have in hand) because it looks new. I am guessing that there was nothing wrong with the original lock body. Any fault is probably in one or the other of the deadbolt actuators. I speculate that someone recently replaced the mortise lock thinking that was the fault when really the fault is elsewhere.

I plan to set the cylinder at the key removal position then retract the key partially so the lock tumblers cylinder won't move and then use the key to thread the deadbolt controller (outside one) back into the lock. When I have it at the right depth and in the right orientation I will tighten the set screw exposed on the edge of the door. Hope this works.

This video details installation of this type of lock. However, I am not sure how to tell if a lock is right handed or left handed. https://www.youtube.com/watch?v=f0YdbsAk0iM

  • The cylinder screwed back in using the key inserted partway to turn the cylinder without turning the tumblers. The lock is now back to the state it was in before I messed with it and it seems to work. So qualified success. – Jim Stewart Mar 22 '17 at 18:30
  • The way that you install the cylinder is that you loosen the one (or sometimes 2 ) locking screws that anchor the cylinder. You then spin the cylinder with the key until it is tight and vertical. You then screw in the lock screw. As an aside: Many of these are reversible. They do, however, break -- one failure that I've seen is that the casting anchoring the springs can fracture, in which case the lock will stop working. – gbronner Apr 17 '20 at 1:19

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