Keeping lock from dropping into door frame

A quick learner from Riverside, CA says:
What is the trick to not dropping the lock in the door frame during installation?
Profile picture of Tom
Tom from SWISCO responded:
Thanks for posting. Your mortise lock is dropping inside your door frame? That probably shouldn't happen; this lock has a faceplate that is wider than the hole. It's possible that your have the wrong lock. If you wish, you can send a few pictures of your lock as compared with the installation slot for us to take a look at.
A home owner from St. Louis, Mo says:
I have a 5500 series sliding glass door, the mortise lick I received is slightly larger than the opening in the door frame. I don't think this is a problem. I can file the door frame opening for the lock slightly and it will fit. I don't remember how the latch moved to the locking and unlocking position, there is no thumb handle to operate the locking lever. It looks like the lock is 55-537 as noted on the shipping order. Please advise about the locking device.
order No. 20079399 customer no. 3452
A home owner from NJ says:
I have the same problem here. The 3-11/16 is definitely the right size but for some reason the whole itself is about 4" in size. On my door it appears thee are holes for some kind of face plat to keep the lock in place. Picture attached.

In theory, the faceplate is not needed because as soon as you install the handle into the lock it keeps it in place. It should only be an issue if you remove the handle and the lock falls into the door (which happened to us).
A customer submitted photo of a mortise lock.
Profile picture of Donna
Donna from SWISCO responded:
Looking at the image you posted with the ruler, it looks like the installation holes might measure 4-5/8" on centers, if they do please take a look at SWISCO product code 82-226, mortise lock with faceplate, as a possible replacement.
A quick learner from St. Louis, Mo. says:
Got the lock installed after a little filing of the opening, but it works great now.I was able to get a long nail thru the locking handle hole and the door jamb to hold the lock in place untill I got the screws installed.
Reply to Thread
* Mandatory fields
Use this form to ask a follow-up question or to share your experience regarding this subject.
(your email address will be kept private and is only used to inform you when a response has been made)
82-218 : Mortise Lock, Round Face, 3-11/16
82-218
Price: $10.92
Mortise Lock, Round Face, 3-11/16"
82-226 : Mortise Lock, 4-5/8
82-226
Price: $13.45
Mortise Lock, 4-5/8"
How to install the 82-034 Legacy Handle Set
Video
How to install the 82-034 Legacy Handle...
How to install the 82-218 Mortise Lock
Video
How to install the 82-218 Mortise Lock
How to maintain a sliding glass door
Guide
How to maintain a sliding glass door
82-034 Legacy Handle Set Installation
Guide
82-034 Legacy Handle Set Installation