The following Kwikset lockset on my front door no longer works well. From the inside rotating handle it's fine. From the outside it's sticky, as the bolt does not fully pull in. This particular lockset replaced an older and more sturdier model a few years back. Nothing inside seems amiss. I've checked the backset and it seems fine.
The problem turned out to be wear. The exterior latch turns a half circle piece of metal, which bears on the latch. Metal on metal, one with a sharp edge? No wonder it wore out:
The upper bearing surface is the factory shape, the lower shows the wear.
The interior handle actuator bears slightly higher and apparently wore more slowly.
Kwikset apparently has a lifetime warranty on mechanical and finish issues. I called them and they readily agreed to send out a new part at no charge with no receipt.
That said, bad design good warranty is an unfortunate policy: the new part will clearly wear out in the same way next time. I will lubricate it, but lubricant only goes so far.
In the interim a paperclip is doing the trick:
