Replace a lock cylinder
Its a mostly simple job to fit a new lock barrel. The lock itself is not replaced, just the barrel, which is bought separately.
Why replace
Apart from the obvious...
A new lock barrel is under £2 for a basic one, or £4-5 for one with hardened pins in 2011. So replacement is often cheaper than copying keys. New barrels usually come with 3 keys, sometimes 2.
When moving into a house, you've no idea who has keys. Its prudent to replace external lock barrels.
Some house insurance policies are invalid if a barrel with unhardened pins is used on an external door.
Gain access
If you're locked out and can't get in any other way, drilling out the lock barrel is usually the easiest way to gain entry. Expect to ruin a few drill bits in the process. 4mm twist drills are good for the job, though if not careful more drill bits will be needed.
Remove lock
There are 2 ways cylinder locks are commonly fixed to doors. Remove the visible screwheads, and either the whole lock will come off in one piece, or most of it will come off, leaving a backplate behind that needs to be unscrewed to remove it.
If the whole lock comes off in one, there is a separate smaller backplate that holds the barrel in place. When the lock leaves a full size backplate in place, the baseplate holds both the barrel and the lock.
Remove old barrel
As you'll see, the lock barrel is held with 2 snapoff screws. Remove these, and the barrel, the ring on the front, and the plate on the rear all come away. Reuse these screws if they're not wrecked, its easier than cutting the new ones to length.
The new lock barrel
They're standardised, so the main choices are brass or chrome finish, and hardened or unhardened pins.
- minimum cost barrels are unhardened, and can be drilled open
- house insurance often requires hardened pins
- hardened pin barrels can be drilled, but its more difficult, and can take a while, and several drill bits.
- unhardened may be preferable for internal rooms & cupboards, a fair bit easier to remove if keys are ever lost.
Its not best practice to have new locks, barrels or keys posted to you, the seller usually has your address, either from the delivery address or credit card details, and there are people that copy keys and misuse them.
Fit new barrel
How it fits in is fairly obvious, ring at the front, plate at the back. Get the new barrel in the right position, not rotated round out of place. There's usually a slight ring indentation in the door, sit the front ring in that to avoid a minor decorating mishap. Often the old front ring looks better than the new one, and on occasion the old rear plate is the only one that will sit flat enough.
Reuse the old barrel fixing snapoff screws when possible, it avoids needing to cut the new ones. If they can't be reused, the new ones can be chopped or sawn at the indentations. Don't try to snap them by bending, a lot of these screws aren't hardened and will bend, ruining them instantly. if cutting screws, look at the cut end afterwards, and if any thread is distorted at the end, file the damaged bit of thread down.
The tongue of the new barrel needs to be cut to length. Mark on the tongue where it projects about half the depth of the lock, and cut it off there. Length needn't be precise. A hacksaw works, but is slow and fiddly; bolt croppers or mini bolt croppers are very quick.
Refit lock
Just the reverse of removing it.
Issues
Issues sometimes encountered:
The new lock is too stiff to turn as far as is needed. If it turns in one direction ok, and opens the lock, no problem. If not, the cause is usually poor alignment between barrel and lock. This tends to give huge variation in stiffness as the key is turned. Slacken the lock barrel fixing and slide it sideways a fraction so it lines up better with the slot in the lock where the tongue goes, and retighten. Oiling the barrel is never the solution. If the amount of stiffness doesn't vary with key position, the fault is with the lock, not the barrel. Open, clean and grease the lock mechanism. Lock parts tend to pop out of place when opened, so probably some people had best leave it alone.
The lock screws won't tighten because the thread in the wood is stripped. Probably the simplest solution is to lightly hammer a matchstick into the hole in the wood door, and snap it off level. Or sometimes slightly fatter screws will fit and grip. Or if the screws are short, fit much longer ones.
Lock won't quite sit flat against the door. This happens when the rear plate that holds the lock barrel fouls the lock. Loosen this backplate, reposition slightly and tighten, or if necessary remove it and put the old one back on instead.
In some situations you might need a new lock that takes the old key. Rekeying a lock barrel is a locksmith's job.
Key needs waggling to turn. Caused by poorly cut key copies.