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The latch bolt in the mortise lock on my front door hangs, presumably because of built up grime. At any rate it gets stuck before exiting the faceplate fully (see picture below), resulting in it not entering the strike plate.

I want to try to clean the lock and then lubricate it, but I am uncertain about the best way to go about it. Can someone here please give some advice on how to best fix my door?

enter image description here

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  • Have you tried wd40?
    – Questor
    Commented Nov 29, 2023 at 16:20
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    @Questor wd40 is not a long term solution for lubricating stuff like this. Commented Nov 29, 2023 at 16:26
  • @ratchetfreak It works wonders for cleaning...
    – Questor
    Commented Nov 29, 2023 at 16:31
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    WD40 turns into sticky goo after a few years. Unscrupulous locksmiths can guarantee repeat business by using WD40 liberally on locks that they service.
    – MTA
    Commented Nov 29, 2023 at 16:51
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    For locks you want a dry lubricant to avoid attracting dirt. If somebody already sprayed WD40 in there, then more of the stuff is might be okay for cleaning away the old stuff plus accumulated dirt. That feels like "doubling down on stupid," however. WD40 actually owns a "dry" lock lubricant brand. That stuff, graphite powder, etc. is what you want if the lock hasn't already been contaminated with oil and dirt.
    – popham
    Commented Nov 29, 2023 at 17:00

1 Answer 1

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To clean the lock: disassemble and remove the handles, loosen and remove the lock cylinder(s) and/or thumbturns (remove edge cover plate, loosen setscrews a few turns, unscrew these from the lock body or in Europe slide the cylinder assembly out), dismount the lock body (remove screws, slide out), open the lock body, remove dirt/dust, check whether springs are still strong enough, check for unreasonable amounts of wear, replace parts that are worn out (if you can), lubricate (see below), reassemble everything in reverse order of disassembly, check that it all works and nothing is loose enough to move in ways it shouldn't or too tight to move in ways it should.

Traditionally, the latch mechanism was lubricated with a light grease. This is not a place where precision matters much; you just need things to slide reasonably easily and not wear out too fast.

Graphite powder used to be the locksmith's go-to for lubricating precision moving parts such as the lock mechanism (the parts that recognize the key). It can still be used, but many (most?) locksmiths have moved to a silicon microsphere lubricant such as Tri-Flo. These go on wet but the carrier evaporates away leaving a dusting of, essentially, microscopic ball bearings. This has the same advantages as graphite but doesn't have the risk of being overapplied, and has some of the same cleaning properties WD40 claims.

(I am not in the no-WD40 camp. If treated as a cleaner, to be followed with the proper lubricant, my experience is that it's harmless at worst.)

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  • Graphite powder is also very easy to obtain in small quantities. Take a pencil, a box cutter, and shave off some lead. See if that helps.
    – Nelson
    Commented Dec 5, 2023 at 3:07
  • Trivia: commercial graphite powder is fine enough that it can be used to lift fingerprints.
    – keshlam
    Commented Dec 5, 2023 at 10:51
  • Graphite powder is cheap at most hardware stores and locksmiths a few dollars for a tube that should be good for many applications if not overapplied.
    – keshlam
    Commented Dec 5, 2023 at 11:12

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