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Lister LH150 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 LH150 has a predominantly rectangular top cover, but with a
triangular section at the rear edge, with the point towards the reduction box or
output flange, depending on type. There is a small dome at the right hand front
corner of the cover. There are two brass plugs (although typically painted over)
on the cover; the larger being the filler plug, the smaller is access to the
hydraulic system and should not be disturbed. The cover is secured by nine bolts.It may or may not have  its original brass ID plate. These have often disappeared.

The small gear selector lever is found on the upper left hand side of the main
casing. This actuates a spool valve within the gearbox, causing one of the three
positions to be selected.

The LH150 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.
If you are lucky, the original brass plate will still be in place with the gearbox type stamped on it.

Lister LH150 --  How it works:

The LH150 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. The shaft also carries a drive gear which operates the gearbox oil
pump. It is important to note that the oil pump is directional, so a replacement
gearbox must be correct for your engine rotation. The vast majority of LH150
are set for clockwise rotation engines. Of the family of engines that used the
LH150, the one exception is the SW series (SW only; not STW). All SW are
anti-clockwise rotation engines.  All the rest are typically clockwise, but may
be anti-clock. With the gearbox removed it is not a difficult job to swap over
the oil pump, if required.

It is important to note that when the engine is not running, the gearbox default
position is forward drive, irrespective of where the gear lever may be set. This
means that when the engine is started, the propshaft and propeller will
momentarily turn until oil pressure is built up within the gearbox.

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.

Neutral and reverse positions are achieved through hydraulic pressure acting
on dedicated pistons and levers; forward is not dependent on hydraulic pressure
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.

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 as the box defaults to 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 selection, necessitating a complete  strip down of the box. Additionally, all the moving hydraulic parts
are susceptible to rust damage. Enough cumulative damage will scrap 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 ! If you have fully drained the gearbox, refill to the dipstick mark, run the
engine for a minute or two, turn off and then re-check the level after a few

           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.

If the boat is not moved too often, when you do go to it, start the engine and run
the gearbox through its neutral and reverse positions. This will minimise the
chance of the forward cone sticking to the drum.

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

Make any adjustments to the gearbox selector piston settings 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.

Attempt to remove / refit the gearbox unless you are confident in being able
to keep it straight and square relative to the engine. Failure to do this may
result in terminal damage to the oil pump drive shaft, which although small
is eye - wateringly expensive !  An LH150 with reduction box is easily around
50kg and an awkward lump to manhandle.

                 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  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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