Model 6730, 6735, 6738, 6741 Mechanical Combination Lock
Troubleshooting/Dialing Diagnostics
stuck fLy
So far, we’ve only checked and corrected problems with external
parts: the dial and ring. There are many more parts inside the
lock which are required to work with much greater precision.
Most locks you will encounter are three-wheel types, requiring
transmission of motion from the dial to the spindle, from the
spindle to the drive cam, from the drive cam to the number 3
wheel, from the number 3 wheel to the number 2 wheel, and
from the number 2 wheel to the number 1 wheel. While this
is a simple explanation of the transfer of motion, there are
actually more parts involved.
Note: The following procedure has nothing to do with whatever
combination numbers we assume have been set into the lock.
Before beginning our diagnostics, it will be necessary to count
the number of wheels in the lock. A good quality safe techni-
cian’s audio amplifier will make the job easier by enabling you to
clearly hear metal-to-metal contact inside the lock.
Turn the dial right (clockwise) at least six times, stopping at
60 on the last turn. Turn left (counterclockwise) to 40. As you
pass the vicinity of 6 and 14, you should feel and hear metal-
to-metal contact. This is the nose of the lever striking the
sides of the drive cam gate. The presence of these “contact
points” tells you that the lever is moving freely on its pivot,
and the lever spring is intact.
Pause at 40 to re-grip the
dial, then dial smoothly
and fairly rapidly to 70. As
you pass 60, you should
again feel light metal-to-
metal contact. This is the
drive cam picking up the
number 3 wheel (which
holds the 3rd number of
the combination) right
where you left it parked.
The contact should occur
between 60 and 62. If it occurs ten to twelve numbers before
60, the 3rd wheel fly is stuck.
Continue dialing left to 40. Once again dial smoothly to 70.
The contact you feel and hear is the 3rd wheel picking up the
2nd wheel (which holds the 2nd number of the combination).
The contact should occur within two numbers of the last con-
tact (drive cam picking up 3rd wheel). If the 3rd wheel picked
up at 60, and the 2nd wheel picks up at 50 or 51, the number
2 wheel fly is stuck.
Continue the same procedure to check the 1st wheel fly. You
should check another revolution of the dial to be sure you are
not dealing with a four-wheel lock. In that case, the wheels
would be numbered 4 – 3 – 2 – 1, with each designation refer-
ring to the number of the combination carried on the wheel.
Wheel number 4 carries the fourth number of the
combination, wheel number 3 carries the 3rd number of
the combination, and so on.
If all goes well, you might feel metal-to-metal contact on the
1st three turns of the dial, at 60 1/2, 61 and 61 1/2. The
fourth turn of the dial will reveal nothing. This most likely
means you have a three-wheel lock with properly functioning
flys. It could also mean you have a four wheel lock with a
broken drive pin on the #2 wheel, but that is very unlikely. The
point is this: Symptoms can point to more than one type of
lock malfunction.
A slightly more likely situation is to observe no metal-to-metal
contact at 60, which would mean the drive pin on the drive
cam is broken, and no motion is being transferred to any of the
wheels. Unfortunately, this calls for forced entry of the safe. A
broken drive pin is apt to be on the drive cam or the #3 wheel.
The farther a wheel is from the drive cam the less likely it is
to suffer from a broken drive pin, because it is moving fewer
other parts and is subjected to less stress.
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© Copyright 2006, Sargent & Greenleaf, Inc.
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