Do-it-yourself replacement of the front door lock cylinder

Recommendation points

• When is it time to change the larva
• Going to the market: how to choose the right replacement
• Removing the old core of the castle
• Installing a new larva
• Abnormal situations and common mistakes

The English larva is one of the most popular and at the same time vulnerable type of cylinder locks. Whatever the reason for replacing it, you can complete the task in a matter of minutes. Of course, if you know the correct sequence of actions, which we will describe for you today.

When is it time to change the larva

Except for such obvious situations as a complete malfunction of the lock or the loss of a key, there are a number of other signs that suggest the need for urgent replacement of the cylinder. It is very important to be able to correctly assess the condition of the core by indirect signs, otherwise the front door may be blocked at one moment and, as a rule, this moment is always the most inappropriate.

The mechanics of cylinder locks are quite thin and the wear of small parts leads to the fact that the pins (pins) do not rise to the required height, respectively, the cylinder is not unlocked. Much can be said about the state of the key: the material from which it is made is approximately comparable in hardness to the details of the larva. However, since one lock is unlocked with several keys, an appropriate correction must be made for the degree of wear.

It is optimal to compare “working” keys from a bunch with spare ones: lack of edge sharpness, loss of height on the protrusions, change in their shape and erasure of the chrome coating – this is what you should pay first attention to. On average, the larva of Turkish and Chinese production lasts from 3 to 5 years, European cores – from 7 to 10 years.

Fortunately, the English larva very rarely stops working suddenly, and there are a number of indirect signs that the lock will soon refuse to open. For example, when the cylinder wedges half a turn and turns to the end only if you shake the key in the well. Other alarm bells can be extraneous sounds – crunching, clanking, creaking – both when the key is inserted and when the lock is turned. Often it is not the secret itself that fails, but the rotary cam of the larva – in terms of transferring mechanical force, this is the most vulnerable part.

Going to the market: how to choose the right replacement

Since you cannot leave the apartment unlocked while you go to the store for a new maggot, the lock will have to be disassembled several times. The first time the larva is removed for measurements, the second – directly when replacing.

A diameter of 17 mm and a height of 33 mm are standard for most lock manufacturers: for Apecs, KALE and the like, the cylinders have exactly this section, and even such advanced manufacturers as Abloy and Mul-T-Lock try to adhere to the general DIN standard for the greatest compatibility of their products. Therefore, if you decide, along with the replacement, to increase the secrecy of your castle by installing a more sophisticated larva, there should be no problems. Rare exceptions include very old locks of Soviet and Finnish production, as well as fire doors, the locks of which have a unique teardrop-shaped cylinder.

Much more important is the section of the larva, its length and the location of the mounting hole. The best option is to put the larva on a piece of paper and trace the outline, not forgetting to mark this very hole as well. No one forbids simply measuring the main dimensions and choosing a replacement for them. There is, however, an important caveat: if the cylinder protrudes too far out of the door, then opening such a lock will be a matter of five seconds. Therefore, it is better if the larva is slightly recessed into the door, and even better, it is completely hidden under the armor plate.

In the store, you will have to face a huge selection of larvae, without known sizes it will be an attempt to find the right component at random

Please also note that the larvae may have a flywheel on one side, and it will no longer be possible to turn them by any side by adjusting the protrusion of the body. The presence of a flywheel is more convenient for interior doors, but on entrance doors, such an addition does not have the best effect on burglary resistance: the most popular way of opening is to drill the door with a crown and open it by hand from the inside. In addition, only a larva without a crank can be blocked from opening with a key..

Removing the old core of the castle

The larva removal process is extremely simple and consists of three steps:

1. Unscrew the bolt from the end of the door, it is usually located above the crossbars, exactly opposite the protrusion in the lower part of the cylinder. The bolt must be pulled out completely.
2. Having inserted the key into the well of the cylinder, we turn it by 10-15? So that the tongue aligns with the body and does not interfere with the extraction.
3. Since in this position the key will not come out of the lock, pulling it out, we remove the larva.

Usually, it is most convenient to pull out the larva from the inside of the door, from the outside the armor plate interferes. The design of doors and locks may differ, and sometimes the larva can only be pulled out to the “street” side, having previously unscrewed the locking screw of the internal flywheel. This usually happens when the decorative cover of the lock on the inside has a hidden fastening and it is easier to dismantle the outside..

The main thing when removing the larva is to remember that it is always removed without unnecessary effort and any stopping indicates that the door or lock is not sufficiently disassembled: the linings are not removed, the bolt is not fully pulled out, the cam interferes.

Installing a new larva

When installing the larva, proceed in the reverse order. It is recommended to first compare the old and new cylinders in terms of size, position of the mounting hole and tongue.

We insert a new larva into the profile well, after turning the movable tongue by the key or flywheel. Slightly moving the larva inside the lock, we are trying to get the bolt into the hole and bait it. If successful, the cylinder will immediately stop moving inside the door. It is not difficult to hit with a bolt, since the threaded hole almost always has a countersink.

After installing the new larva, we check the operability first in the open state, then closing the door from the inside, then we try to lock it from the outside. There should be no extraneous sounds when locking and unlocking, the cylinder stroke when turning the lock is free and absolutely without vibrations. The same is true when inserting the key – the new larva always features absolutely smooth running and a complete absence of backlash.

Abnormal situations and common mistakes

For the entrance doors of private houses and summer cottages, the following incident is common: due to corrosion, the fastening screw boils strongly, and after licking the slots it cannot be removed in any way. In this case, the larva will have to be broken and it is very good if the door turns out to be open at the time of replacement. Having removed the armor plate from the outside (if any), you need to grab the protruding edge of the larva with an adjustable pliers or pipe wrench and turn it sharply. The weak point of any cylinder is in the narrow neck in the place where the bolt hole is made. If a crack appears here, the mount will loosen and the screw can be removed..

Another unpleasant situation is when the key breaks in the lock. Removing the debris is almost impossible, but often it is not required. Since the cylinder remains unlocked, it can be rotated with considerable force, for example by inserting a flathead screwdriver into the hole. It is only important not to push the piece further than the intended one, otherwise you can also resort to breaking the core for its protruding part.

The surest way to open a lock with a faulty cylinder is to simply drill out the pins. It is necessary to mark with a drill in the protruding part of the larva, where the manufacturer usually puts a stamp. The thickness of this part is 10 mm, respectively, a drill of at least 6 mm is required for breaking. The details of the core usually do not differ in particular hardness (hence the low burglary resistance), but care must be taken that the drill does not go to the side. The passage of the drill through the pins is quite felt with your hands, it will be enough to drill the secret only on one side.

Finally, do not forget that the safety of the larva largely depends on the operating conditions. It is impossible to lubricate the internal mechanism from the word at all, a small amount of lubricant is allowed only in the cam gear. You also need to always monitor the cleanliness of the keys and check before opening the door: whether a foreign object is inserted into the well, in the form of a match or a nail..