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Lister LM100 Marine Gearbox

We hope the photograph will have helped in confirming the identity of your gearbox.  There is often confusion between the LM100,  the LH150 and the SL3
gearbox. (not to be further confused with the SL3 engine !)

At a glance, the LM100 has a pretty much flat top cover, secured by a bolt at each corner, with a filler plug in the middle. It may or may not have  its
original brass ID plate. These have often disappeared. A gear selector cross shaft protrudes either side of the box, just below lid level and the hand
operated gear lever will be secured in one of the two available holes in the shaft. Typically, these boxes will be operated directly using the main external lever.
Remote operation is possible, but a substantial linkage is required as there is a relatively high effort to work the lever. If you have a single lever Morse type control
which does both throttle and gear selection, you almost certainly do not have an LM100.

The LM100 was available as a direct drive unit or with a reduction box of 2:1  or 3:1 ratio.  The photograph shows a reduction box fitted. It is
important to note that it is not readily possible to convert between direct drive and reduction drive in an existing installation as there is a difference
of around 3.5 inches in the output flange heights. Otherwise, converting either way is relatively simple.  3:1 reduction boxes are significantly scarce.
Where a reduction box is fitted, a further simple check to distinguish between the LM100 and the earlier SL3 gearbox is to count the bolts on the output flange.
If original fittings, the LM100 flange has six bolt holes while he SL3 has four. This test does not apply to direct drive boxes as in both cases a four bolt flange
was used. In this case, to positively identify the box the output flange should be removed and the shaft diameter measured. The LM100 shaft is 1.375 inches
diameter, while the SL3 shaft is one inch. If you are lucky, the original brass plate will still be in place with the gearbox type stamped on it.


Lister LM100 --  How it works:

The LM100 is a relatively simple, three position gearbox:  Forward, Neutral, Reverse.  Power is transmitted to the gearbox from the engine by a solid shaft,
bolted to the engine flywheel and with a set of gear teeth cut at the gearbox end.  There is no drive plate between the engine and gearbox. The shaft mates with
a set of internal epicyclic gears which are part of the gearbox drum and hub assembly. In neutral with the engine running, the hub assembly spins but no drive
is transmitted. When forward is selected, a spring pack on the mainshaft pushes a clutch cone into engagement with the tapered internal face of the drum. As the
clutch cone is splined to the mainshaft, once it engages, the motion of the hub / drum assembly is transmitted to the mainshaft.

To obtain neutral from forward, a thrust bearing pulls back on the clutch cone, disengaging it from the drum.

Reverse is achieved by the action of a brake band gripping the outer face of the hub/drum assembly. With the drum unable to turn, the epicyclic gear train comes into play, transmitting drive in the reverse direction via a gear on the forward end of the mainshaft.

All three positions are obtained by the action of a pair of  rollers acting on profiled levers. The reverse brake band has a natural springiness to the disengaged
position, plus an additional retraction spring.

In either the direct drive version or the reduction box version, a thrust bearing is fitted immediately behind the output flange capable of taking all forward or reverse thrust.


What are the common problems ?

We see quite a lot of these boxes and by some margin the most common issues are loss of reverse;  loss of forward;  inability to obtain neutral, often accompanied
by engine stalling if reverse is selected.

Loss of forward.  Original cones had rivetted linings and in older boxes these linings may start to break up simply due to age, or be worn beyond serviceable limits
                             through  use.

Loss of neutral /  engine stalling.  This is closely related to the issue above, of linings breaking up. If a piece of broken lining wedges between the clutch cone and the drum
                                                       even when neutral is selected, forward drive may continue to be transmitted. If reverse is then selected the epicyclic gear train is unable
                                                       to function correctly and the box simply locks up, stalling the engine.

Loss of reverse.  Almost always due to a worn out friction lining on the reverse brake band. The friction lining on the band is very thin and unless slippage is detected
                            very early on and the band adjusted correctly, it will be beyond saving.

On the one hand, these are significant faults which render the gearbox unusable, but do bear in mind that very often the box will have had little or no attention for very many
years and is likely to have outlived almost any comparable age unit. All the above are fixable, but all require a strip down.  Once repaired, if done properly, the box will be good for many years further service.

General wear is the next most prevalent issue, including worn bearings, bushes, gears and sometimes the hub/ drum itself. The good news is unless left to an extreme condition,
none of these things will rob you of drive. A useful and simple test is to grasp the output flange (with whatever it is coupled to unbolted) and check for any lateral movement
 or evident rotational noise or roughness when turning by hand in neutral. Readily perceptible lateral movement, noise and roughness almost inevitably indicate a box
in need of some renovation.

Water !  As these boxes often live in environments where water accumulates, it is not unknown for them to become submerged.  In the event you find evidence of water in
              the gearbox (milky, emulsified oil  -- or just water), it is important to drain the box as soon as possible and flush it with clean oil until all traces of water are removed.
             Apart from the obvious negative effect of water and rust on all the machined moving surfaces, the real danger is that if the box happens to be left in the forward
             position  the clutch cone may rust to the drum. This can be a sufficiently strong bond that it is impossible to free it using the gear lever, necessitating a complete
             strip down of the box.

Things to do and not to do:

DO --  Make sure the gearbox and reduction box contain the appropriate amount of clean oil.  SAE80 or SAE90 Gear oil is fine in both boxes.
           If you have the original brass plate it may say use engine oil in the reversing box; this was later changed to the specification above. Each box has its own dipstick.
           Find it and use it !

           Make sure the engine installation is such that the gearbox output flange and whatever is connected to it are perfectly aligned. The flanges should be perfectly flat
           to each other and the bolts go through their holes, by hand, fully. Misalignment here will cause premature wear to the gearbox and likely the stern gear. Flexible
           propshaft couplers are no substitute for basic correct alignment, unless they are a properly engineered double jointed assembly, using a separate thrust plate.

          If the engine appears to be labouring and / or black smoking. With the engine turned off and the gearbox set in neutral, check that the propshaft rotates freely.
          If not, check for a fouled propeller.  Make sure no one can start the engine or engage a gear while you are doing this.

DON'T  --  Try and free a fouled propeller  by constantly alternating between forward and reverse. If a good blast in reverse does not clear the prop, best to physically
                   remove whatever is causing the problem.  The reverse band has only a thin lining and will not stand over much abuse.

                  Leave the gearbox in forward if you are not using the boat for some time.  If there is moisture present in the box, there is a chance of the clutch cone sticking
                  to the drum.  If you go to your boat but are not moving it, it is a good idea to start the engine and run the box through its positions to keep things free in the
                  box.

                 Make any adjustments to the gearbox selector rollers unless there is a good reason. Any signs of slippage in forward or reverse should be investigated
                 quickly, but otherwise ---- if it's not broken, don't fix it.

                 Use any additives in the reversing gearbox.  They may glaze the linings, causing permanent loss of drive.

                 Throw away your old Lister gearbox if you are swapping it out for something different.  Give us a call.
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Parts Availability.

                              With the exception of the bearings and seals, every other part of the gearbox is a Lister specific item and the majority have not been supported for some
                              time. We keep stock of service exchange clutch cones and brake bands plus bearings, bushes, seals and gaskets. We also stock core unit gearboxes and
                              reduction boxes for full reconditioning.

                             If you are shopping around for bearings, you need to be aware there is a dramatic difference in quality between those from a reputable manufacturer
                             and those (typically) of Chinese origin. Some of the bearings are significantly expensive, but given the work involved in a rebuild and the effort of
                             removal and refitting it is an area where it is absolutely not worth economising.  As a rule of thumb, if the bearings aren't made in Europe, Japan or
                             North America, you probably don't want them.


Top Tip !
                            We all like a bargain and if your box is playing up you may be inclined to find a usable second hand unit.  Just remember that the youngest of these
This page is the property of Listerparts.co.uk. No reproduction without prior approval and visible credit
                            boxes is likely to be pushing 40 years old, so you do need to be sure before buying that your prospective purchase actually works. If it is being sold
                            as rebuilt or having had attention, don't be afraid to ask to see the receipt as evidence of what has been done.


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