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The latch bolt of the mortise lockset in a metal security door is stiff. I worry about the long-term effect of slamming the door in order to drive the stiff latch bolt back and allow the door to close in its frame.

There is much discussion of lubricating the pins and the cylinder of the keyway, centering around the pros and cons of graphite and non-greasy lubricants. But there is no discussion of how to lubricate the portions of locksets which are not along the keyway.

I plan to remove the mortise lockset and, hopefully, open the case to expose the latch bolt mechanism. Can I assume that the latch bolt mechanism is simply a moving metal part in a metal housing and lubricating it is unrelated to the controversy over whether graphite or graphite-substitutes are appropriate to keyways?

What to you think of this plan? Disassemble and clean the latch bolt parts. Remove dust and dirt along the moving path of the latch bolt. Lubricate the latch bolt mechanism either with oil, or possibly grease it?

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Yes, this is just a lump of metal, big enough that it doesn't matter a lot what you lube it with. (I'd lean more to a grease than an oil -- lithium grease used with a light touch, perhaps.) But it also shouldn't need lubrication on a regular basis, so I suspect you've got something else going on.

  • I read often in older how-tos of graphite as the lubricant of choice, but this lubrication from the past seems to have fallen on disfavor. I suspect people chose it assuming that maintenance is rare or never. Grease and oil might work well, but require more frequent cleaning to avoid gumming up with dirt? – George Snead Aug 2 '15 at 3:37
  • It's a religious debate.... I'll expand upon my answer but basically it has to do with how various lubricants respond to dirt, moisture, and temperature. I don't agree with the critiques of graphite unless it's overused... but it's relatively easy for novices to overuse in a lock. – keshlam Aug 2 '15 at 15:09
  • I did try to lubricate the mortise lockset, but was unable to remove the cover on the case. Subsequently, I blindly blew in silicon lubricant thru openings in the case. Not a good technique, but I needed to ease the stiffness in the bolts. Later, I found servicing instructions on a webpage for reversing the latch-bolt. This process includes opening the case, which befuddled me earlier. It turns out that a third screw secures the case and its hidden under the paper label that identifies the model type! Also, the dead-bolt should be extended with a push thru the cylinder hole. – George Snead Aug 7 '15 at 21:12
  • Screws hidden under labels should always be suspected; it's an easy way for a manufacturer to know if someone opened the case. – keshlam Aug 7 '15 at 21:36

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