There are a couple of painted shut unused dead bolt (mortise?) locks in my flat attached to internal doors that are so ill fitting they stay shut anyway. Also they are mine and I dont mind, so a couple of days ago I cut some spokes off a rusty old bike in the garage.
A while of prodding at one of these with a bent spoke or two revealed no insight, they must be 20+ years old anyway so today I removed one and had a look.
Thought I might as well share.
Here it is straight out of the door. Some of the screws had to be dremeled loose because they were so rusty:

And with the front removed:

Here we see the warding, which makes me think the key might've looked something like this wonderously creative artists impression



The bolt removed and a bit of a clean, revealed a single lever. There is an appropriate nodule on the reverse of the bolt and no "gate" as such so the lever only has to be lifted far enough to clear it. There are no measures to prevent an over-lift apart from the insanely tensile strength of the spring.

The next photo shows how I was just about able to operate the lever with a bent spoke and take a pic at the same time:

The thing that surprised me was the amount of force necessary to lift the lever, without taking it apart I wouldn't have known to push that hard.
I have since found the lever on my other internal door but the force required is similar and creating a tool effective enough to hold with one hand, able to operate from either side, whilst manipulating the bolt will be an experiment. Again it's painted shut so I dont expect i'll bother. Maybe at some point ill get round to making a couple of keys, that would be fun.
My guess is that with a new proper lever lock the force required would be considerably less. Hopefully I'll find or get one soon.
Any advice gratefully received.
All pics taken on a Sony ericsson k800i phone, set to "Document" with no flash.