Replacing an odd sized mortice lock.

2 Feb 2020
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United Kingdom
Hi all. This is more a question on why rather than how, but anyway the mortice lock on my front door jammed up the other day finally. It's been dogey for a while but luckily it broke after I unlocked it so I didn't need to call a lock smith.

I thought I'd replace it myself as I've done it plenty of times before, but I measured the old mortice lock and it is 64mm case size, but has a 40mm backset.

For the life of me, I cannot find a replacement that fits these dimensions with that backset, and the hole in the frame is built for those dimensions so I cant put anything bigger in it (I tried a 67mm case size lock I had and it wont fit). Should say at this point the door has a metal frame, it's not wooden.

It seems like every lock I can find in 64mm case size has at least a 45mm backset and every lock I find with a 40mm backset only comes in 67mm case size (or larger).

The broken lock doesnt help either, there are literally no markings on it at all, no model names numbers makes, it's completely blank and generic looking.

Clearly I'll end up getting a 64mm case and 45mm backset lock and have to cut the keyholes again and somehow cover up the mess, but I just wondered if anyone could shed some light on why no manufacturer apparently makes locks in these dimensions. Cheers!
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sorry to hear there are no markings on your old one. Please post a photo of it, with dimensions, and of the key, showing any markings, and of the frame showing the current hole.

Is it a metal door?
I didn't think of that, or looking at the keys (d'oh). I'm not at home atm so can't show pictures of it but I looked at the key and sure enough theres the make. It's a chubb.

Based on all this I may have actually found a replacement made by union on amazon of all places! Excellent. Thanks very much for tge help guys.
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Is it a 3G114E?

makers name should have been on the brass or stainless frontplate

The new one has a bigger bolt than the old (BS has been improved for greater strength) so you may need to file the frame a bit.

I have them on my back doors and shed, you can get them suited to the same key if you have several, so you only need one key.

Very good lock. It's the Chubb design, Union used to be in the same group, but the licence to use the Chubb name expired.
Yea that's the one. It initially through me off because it stated it was 67mm but I bought it anyway seeing as it seemed like an identical lock, but upon ariving it is pretty much identical to the old one in size so, either they're including something else in the 67mm measurement or my tape measure is 3mm out of whack. Either way all sorted. Thanks all for the help.

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