Mark IV Manifoil
Chubb Mark IV Manifoil
The following text and images were submitted to LockWiki by Tom Eklöf / obrotund, 21 March 2021:
3 wheel high security lock that has – as the name suggests – features to foil manipulation. Despite having 3 wheels combination has 4 numbers and is dialed like a 4 wheel safe (5 right, 4 left etc) but the last number depends on lock orientation and is not changeable by the user. The forbidden zone also depends on this last number.
Last numbers per orientation
RH – last number 0, forbidden zone 95 – 10 VD – last number 25, forbidden zone 20 – 35 LH – last number 50, forbidden zone 45 – 60 VU – last number 75, forbidden zone 70 – 85
Lock with back cover on. Code # 20 42 1726 from 1978. No R at the end of the serial number so the lock likely hasn't been refurbished. Change key hole is hidden under a spring-loaded cover on the upper left
Bottom of lock, bolt on the left and unlocked. Note the Manifoil / Mersey / Chatwood Milner footprint, ie. Manifoils aren't compatible with Euro footprint / Magic Module without a conversion plate.
Back cover removed.
A: bolt. Unlocked
C: the eccentric (ie. off-center) primary cam. This is the drive cam that is directly attached to the spindle. Eccentricity can be seen by looking at the edges of the middle part on the cam
D: 2x friction rollers
E: zinc and lead shielding to prevent radiological attacks
F: change key hole in shielding
More pictures of the lock can be found in the Disassembly section.
Manipulation resistance features
The split cam
When the secondary cam is positioned for taking readings, the nose rests on the primary cam and the fence isn't in contact with the wheel pack. While the secondary cam contact points can be felt, they don't measure the wheel pack so they're likely not useful.
This means that using the cam gates and lever nose to get information out of the lock directly is much, much harder. The nose does drag on the primary cam and this could be felt as increased friction and would give away information on how deep the nose has "sunk" if it wasn't for the next manipulation resistance feature.
Adding friction at a few different points masks what little information you could get out of the lock. The of these points is the dial.
Dial in dial ring
Disassembled dial. The dial ring can be seen on the bottom of the picture, and it has a separate lead shield and a mechanism for adding friction to dialing. The part on the right is the closest to the container and has a lead shield in it.
Dial ring. In the middle is a part that increases dial friction by pressing the plastic tube onto the spindle. Around it the lead shield.
So the dial itself already adds friction to make getting readings out of the lock harder, but in addition to that the lock mechanism itself has two friction rollers that are pressed into the primary cam by springs. They add both friction and noise.
Friction rollers on both sides of the primary cam. They only touch the primary cam.
Disassembling the Mark IV is fairly easy, although you'll likely want circlip pliers to get some retainer clips off the wheelpost. Other than that you'll be good with a flathead screwdriver to get the lever screw off, and a small (PH4-ish) flathead for removing a friction roller and maybe helping with getting springs off / back on.
The following photos give a 360° view of the insides after the cover has been removed.
Right hand view showing part of the shielding and the other friction roller. Note how the spring is attached so you can get it back on.
Left hand view, showing bolt, lever screw, lever spring, lever, part of the wheel pack and more shielding. Note lever spring position.
Vertical down view, showing friction roller, bolt, lever screw and lever. Roller spring position can be seen again.
Secondary cam gate is at the nose.
The primary cam's underside has a drive pin as usual, this time it just doesn't drive the wheels directly but the secondary cam underneath it.
Closeup view of lever spring.
Lever with screw
Next step is to remove the friction rollers.
The bigger one pops off with just a pull, but again be careful with the spring.
The small roller requires a screwdriver and a bit more care with the spring.
Only the secondary cam and wheelpack are now left.
Closeup of retainer clip, fly and the washers under the fly (might just be one washer in your case.) Getting under the side of the clip via the notch in the wheel post is also possible with a thin hook tool, but I just used circlip pliers.
Once you get the retainer clip off, these are the parts you'll see in order from left to right. Note that the fly's "nose" points down.
Now you can remove the secondary cam.
Underside of secondary cam, showing drive pin that actually drives the wheel pack.
Under the secondary cam there is another retainer clip and then the 3rd wheel's fly and its washer
Closeup of wheel fly. Flat unlike the cam fly
Under each wheel you'll find a washer, a fly and another washer.
The "top" side of a wheel with place for fly at around 9 – 11 o'clock in the center.
Bottom of wheen with drive pin at around 12 o'clock in the center.
Under the 1st wheel you'll find a tension washer that is used to adjust how much torque you need for the wheels to turn. Extremely simple, just a bent washer that you bend more if you need a stiffer wheel pack and straighten out if you need it looser.
The change key hole is behind a spring-loaded cover
Change key compared to 3 wheel S&G