Broken lock please help

[timothydoran]

Just went to lock the door for the night and it felt a bit strange. Then I realised it was jammed. Managed to unjam it with wd40 and curses, but I dare not lock again.

I want to get a new mortice lock tomorrow but it appears to be a 40mm backset which seems to be an odd and expensive size. Also not able to source one tomorrow.

Will I get away with moving the holes 5mm and fitting a 45mm backset lock? Not bothered about the handles, of those have to be changed too, to cover the change. Very happy with a bit of chiseling if that's needed.

Attached a picture in case that helps.

Thanks for any advice you can give.

 

[JohnD]

Please show us some photos of the lock, especially the fore-end plate on the edge of the door, which probably shows the makers name

When you take the lock out, the colour of paint, and screw patterns, will help identify it. Also the key, both sides.

Measure the backset in inches, to the nearest sixteenth of an inch, and the size of the case.

How old is the house?

Is this the front door, needing a secure lock?

 

[timothydoran]

Please show us some photos of the lock, especially the fore-end plate on the edge of the door, which probably shows the makers name

When you take the lock out, the colour of paint, and screw patterns, will help identify it. Also the key, both sides.

Measure the backseat in inches, to the nearest sixteenth of an inch, and the size of the case.

How old is the house?

Is this the front door, needing a secure lock?

Hi John, thanks for getting back.

That's a good point, photos of a closed door probably no use to anyone. Here are some more photos.

I think it is one of these but it's quite pricey
https://www.locksonline.co.uk/Chubb-3K75-5-Lever-Sash-Lock.html

Would you advise getting one of these or fitting a 45mm backset?

 

[JohnD]

yes, I think it is a gold-painted 3K75 (simplified version of 3K74, which is painted grey).
Yours is the usual 2.5" case (there is also a 3")

They are still available but rather expensive (now branded as Union). It's a very good lock and the roller latch has a better action than others. If it's on a front or back door and you need an insurance approved BS3621 lock, the 3K74E is the one.

There is a copy made by Zoo at a lower price.
https://www.ebay.co.uk/itm/Zoo-3K74...325104?hash=item4b7d18cf30:g:e4kAAOSwL3FfA4U5

But yours is a Chubb model and they very rarely go wrong. Do you want to open it and show us what's happened? There are three very small stainless CSK screws on the other side, use a PZ screwdriver of exactly the right size and press hard, or you may burr the heads.

I might have a used 3K74 lying around.

 

[timothydoran]

I have to dash to the recycling centre now, as they are doing bookings only. But here is another photo of inside the lock. Nothing obvious but there is a build of swarf which might suggest it's worn.

The symptom was that it was really stiff, then when it did move the key turned passed its maximum rotation and didn't want to turn back.

Found a better price which I can cope with.
https://www.ironmongerydirect.co.uk...ck-67mm-case-40mm-backset-satin-chrome-150564

Any thoughts