Lister Marine Gearbox Type SL4

[RLWP]

Rather than the bevel gears of a Parsons or the layshafts of the PRM, the Lister box uses a sun and planet arrangement to create reverse:

 

 

In the centre is the gear on the end of the output shaft. Missing is the gear on the end of the crankshaft, this stays on the engine with the oil seal.

 

Outside of the input and output gears are two pairs of gears carried on shafts in a casting:

 

 

The long gear engages with the output gear and the idler gear. The idler engages with the input gear:

 

 

With any gear train, an odd number of wheels means the input and output go the same way around, an even number means they go in opposite directions. We have input - long gear - idler - output. That's four wheels, which is an even number, it's a reversing gearbox!

Edited July 22, 2012 by RLWP

[RLWP]

To get forward, this box locks the input and output shafts together with a cone clutch:

 

 

As it is a proper marine box, it uses springs to hold the forward clutch in engagement:

 

 

If the lever breaks, the band brake packs up, the change mechanism falls apart, the gear clusters explodes, this gearbox gets you home (in forward - don't hit the quay).

 

The box gets reverse by locking the casting to the casing with a band brake:

 

 

As it arrived, it had been unsuccessfully modified, omitting the spirng to pull the bandbrake off:

 

 

Unfortunately, this meant a new bandbrake and a handful of other parts. The bandbrake anchors to the casing with a hefty pin:

 

 

and operates on the outside of the gear cluster casting:

 

 

Richard

[bigkicker]

If you ever need a clutch relining for this gearbox, contact these guys, http://www.industrialbrakes.co.uk

I had one done by them a while back and had a pattern made for it to fit, they still have the pattern, and a reline would be around £40.00 - £45.00, cheaper than a new one - If you could get one !#

[Grace and Favour]

Excellent article Richard - - - -

 

 

(I'm not surprised the unit didn't work when it arrived - I've not come across a bandbrake spirng in many years)

 

 

[RLWP]

Excellent article Richard - - - -

 

 

(I'm not surprised the unit didn't work when it arrived - I've not come across a bandbrake spirng in many years)

 

 

 

Ah well...

 

There's more to come on the change mechanism when I get around to it

 

Richard

[RLWP]

Here we have the forward springs installed:

 

 

Compressing these springs is a bit of a fiddle involving tightening up the nut on the output shaft, putting in the gear change shaft, then taking the nut off, fitting the key and tightening it up again.

 

I had a momentary lapse of reason when assembling this:

 

 

 

Richard

Edited July 27, 2012 by RLWP

[luctor et emergo]

Is the box still in pieces? We need to know...

[RLWP]

No, box went back into a concrete narrowboat and cruised off towards London some time ago

 

Richard

[Tomahawk]

OK just had a bit of a clunk moment..

 

I have a little boat with an SL4 gearbox and the reverse clutch has just parted company.... from itself

 

Is it a huge job to take it out and replace the broken bit..

 

 

[RLWP]

OK just had a bit of a clunk moment..

 

I have a little boat with an SL4 gearbox and the reverse clutch has just parted company.... from itself

 

Is it a huge job to take it out and replace the broken bit..

 

Not too bad. You can take the reverse band out without having to remove the main shaft

 

Richard

[Tomahawk]

 

Rlwp,

 

Thanks for that. I took top top cover off to have a look at the clearances on the levers.. and the lining band was already self removed... as in it was round the back of the main cone.

 

I am assuming this is a gearbox out job... Or can it be done by removing the reduction box and getting at things from the back?

[RLWP]

Gearbox out I'm afraid

 

Richard

[Tomahawk]

Pictures will follow...