Thu Jun 06, 2013 9:02 am by rai
Don't ever buy any lock you intend to use for security with a bitting like that.
notice that the cuts generally slope toward the tip of the key, and the third position is the only one that is slightly deeper than the one on the tip side of it.
such keys can wear along the peaks that are between the bittings or if copied to a second or third generation (copy of a copy) these peaks can simply start to dissapear,
what then happens is you get a key that can be pulled out of the lock without the plug being in the top dead center locking position,
I once had such a key on the door of a rented apartment in a building of apartments, (masterkeyed) and one day I came home and found my lock picked, the core was turned, but it was turned toward the locking position. Not a mistake a lockpicker would make, if he picked it to relock, he would then have relocked it.
I figured out that as I locked the door with the key, I was turning away from the door and starting to walk away, and accidentally pulled the key out leaving the plug turned toward the unlock position.
file off that peak between the third bitting and the one nearer the tip of the key and see if you can pull it out in an unlocked core position, (this loses only that one peak and is done to see if the third pin will ride over the other bitting and let the key pull out, {it looks like a new lock and key so likely you have two keys, the experiment would only alter one of them in an insignificant way}
if not, that is all the other peaks and possibly the difference of the third bitting being slightly lower that prevents it.
besides the weakening of the lock that can be caused by masterkeying, there is also the yale habit of champhering the pins at the shearline and the rounding of the pins where the key rides on them that can cause this defect.
your lock might not have it,
a piece of half inch wooden dowel will make a nice plug follower for it, make it about 3 inches long, no less, a follower is longer than the plug usually, and wood can be shaped on one end if necessary,
An emergency plug follower that I have seen on the forums is a piece of stiff plastic sheet that is simply rolled up to fit the cylinder. work over a towel, not on a hard flat smooth surface as all the little parts will bounce and roll away, A piece of corregated cardboard such as found in packing for a new lightbulb will make a nice tool to sort pins into collumns with their springs.