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Lister LH500 / LH5 Marine Gearbox

The Lister LH500 (or LH5 as it appears in some manuals) Marine Gearbox is the standard fitment for the HRS6 (Turbocharged) and optional on
the normally aspirated four and six cylinder HR and HRW series.

It is mounted at the flywheel end of the engine and is a self contained unit with its own oil supply and final output gearing as an integral part of the whole assembly.

The LH500 was available as a direct drive unit or with a reduction ratio of 2:1  or 3:1. 
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Lister LH500 --  How it works:

As with all Lister's own marine gearboxes,  a drum assembly fitted with an epicyclic gear train is utilised to allow for the selection of reverse.
Forward is achieved using a dedicated clutch housing and multi plate clutch assembly. 

The LH500 utilises oil pressure, generated by an internal oil pump, to achieve forward and reverse. With the engine off, neutral is the default position. The oil pump
is driven by an internal drive gear, which turns whenever the engine is running. A piston  concentric with the mainshaft pushes the multi disc clutch pack into engagement
and forward drive is transmitted by means of externally toothed  clutch plates in permanent engagement with the clutch housing (which is always rotating when the engine is running)
transmitting drive to internally toothed plates which are in permanent engagement with the mainshaft.  When the oi pressure is removed from the piston, a spring pack withdraws
the pressure plate, allowing the clutch plates to freewheel relative to each other and no drive is transmitted.

Driven by an internal extension gear, the reversing brake drum also spins whenever the engine is running. With neutral or forward selected, it freewheels on the mainshaft.
When reverse is selected, a dedicated piston actuates the drum brake band, stopping the drum turning. The epicyclic gear train then comes into play, acting on a gear splined to the mainshaft,
giving reverse rotation of the shaft.

There is a pinion gear on the outer end of the mainshaft, forming one half of the output gear set., the shaft terminating in a roller bearing housed in the rear cover.  The main output
gear sits on a dedicated output shaft / flange assembly, carried on two taper roller bearings, with provision to adjust the bearing preload.

Gear selection is by means of a valve assembly attached to the top of the gearbox housing.  In either air or water cooled engine applications, the gearbox oil is taken through an
appropriate cooler. The oil is also filtered by means of a readily accessible spin on filter.

In the event of the loss of hydraulic pressure, there is provision to lock the gearbox mechanically in forward drive.

What are the common problems ?

We have seen so few of these boxes and receive so few requests for parts or information that we are not sure whether a.) they just don't break, or b.) they produced very few of them.

We would welcome any input that may be helpful.

Things to do and not to do:

DO --

Adhere to the oil and filter change intervals. 

Check the oil level on the dipstick just as you do for the engine.  If the gearbox is losing oil, the cause should be investigated and rectified.

           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 drive is lost, be sure to check for any failure in the external oil cooling circuit,leading to loss of oil.

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. 

Make any adjustments to the gearbox reverse brake band unless there is a good reason. Any signs of slippage in reverse should be investigated  quickly, but otherwise ---- if it's not broken, don't fix it.
Use any additives in the gearbox oil. Additives may glaze the linings, causing permanent loss of drive.

Use more than the minimum amount of power necessary if the gearbox is in the emergency locked ahead position. The fact that
the hydraulics have ceased to give you drive indicate a significant oil issue and general lubrication may be impaired.

                 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.   New, old stock availability is poor. If you have a problem with your box, please call. Most things
we are able to sort out, but be aware that items made to order are likely to be expensive.
Periodically, we have core units for rebuild and may then be able to offer a complete gearbox on an exchange basis.
                             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 !        

These gearboxes are a scarce item (at least in the UK). If you run one and someone offers you new parts for it,  or a complete
spare, bite their hand off !
If you really don't want them,  we are always interested for stock.

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