Lister LH150 Reversing Box

[WotEver]

It's possible that the reduction version of the box, which we don't have drawing of, doesn't have the mauve bearing, it relies instead on the reduction box bearings.

Gotcha

[paulcatchpole]

Probably not much help, but I still have the manual for a Parsons box.

 

The way that worked was there was always a bearing present, but it was a "special thrust bearing" if the gear box was configured for direct drive, but a "plain journal bearing" if a reduction box was fitted.

 

The manual spells out, (IN CAPITALS), that it one has to be removed, and the other substituted, if a reduction box is being added or removed.

 

There is incidentally something similar for the output of the reduction box, that also normally had thrust bearings. If your prop-shaft included it's own, then, (IN CAPITALS AGAIN!), you had to modify the bearing in the reduction box to a plain journal one "of similar dimensions".

 

Interesting Alan!

 

Admittedly, I can't think of a good reason for that, but then again, I'm not much of an engineer with all this clever stuff.

 

I reckon the reverse box has a split race thrust bearing, as well as the reduction also have a thrust bearing too. Can't remember the reduction box instructions mentioning swapping that bearing out in the case of needing an external one.

 

Wonder why Parsons say what they do?

 

Interesting stuff though!

 

PC

[alan_fincher]

Interesting Alan!

 

Admittedly, I can't think of a good reason for that, but then again, I'm not much of an engineer with all this clever stuff.

 

I reckon the reverse box has a split race thrust bearing, as well as the reduction also have a thrust bearing too. Can't remember the reduction box instructions mentioning swapping that bearing out in the case of needing an external one.

 

Wonder why Parsons say what they do?

 

Interesting stuff though!

 

PC

 

I'm not a mechanical engineer either, but assume that if there is going to be a sideways thrust on a bearing, then it can't be of a plain design, whereas if you have a thrust bearing it must have a sideways force applied to it to keep it in good order.....

 

However, it always troubled me that whilst in forward gear you are attempting to force that bearing further into the gearbox, whereas in reverse you are trying to drag it out of it! Are they designed to work with a sideways force in both directions ?

 

Engineers, please!.......

[MoominPapa]

However, it always troubled me that whilst in forward gear you are attempting to force that bearing further into the gearbox, whereas in reverse you are trying to drag it out of it! Are they designed to work with a sideways force in both directions ?

 

I don't know if you can get thrust bearings which work in both directions, but since almost all shafts need at least a bearing on each end, presumably you could use one for thrust in one direction and the other for the opposite direction? Though then you would have to worry about differential thermal expansion of the shaft and the case.

 

MP.

[springy]

<snip>

What about arranging some load on the output of the reverse box (or reduction if it's back on)?

 

Perhaps even ensuring the engine won't start, lock the output and turn the engine over on the starter, well *try* and turn it over? Might just unstick the stuck bits.

<snip>

 

 

If you can arrange some "load" then OK but I would be very wary of "locking the output" even

if you do ensure the engine can't start. I think the essence of this is that the CONE is stuck,

and unfortunately a cone will tend to pull itself together under load - this is why a cone is

used but also why they have a tendency to stick.

 

What might work is this - lock the output shaft (in Both directions), insert bolt B to overcome

the spring pack and then rock the engine back & forth somehow at the same time as (if possible)

trying to encourage the cone to disengage.

 

Partly an aside but relevant to all this - when you start an engine with an LH150 you will always

briefly get forward drive untill the pump in the gearbox builds up enough pressure to disengage

the drive.

 

springy

[tom_c]

the parsons box has a bearing with a split inner race when set up for direct drive, in this configuration there will be relatively small radial loads on the bearing (weight of propshaft) but the propeller thrust applies an axial load to the bearing. when fitted with a reduction box, gear separation forces come into play and apply a larger radial load to what was the output bearing, with its split inner race this is not a good idea! the plain bearing fitted in its place can cope with a much larger radial force. the only axial force depends on whether the reduction gear uses helical or straight cut gears hope this helps but i know its not really relevant to the lister box, tom

[paulcatchpole]

the parsons box has a bearing with a split inner race when set up for direct drive, in this configuration there will be relatively small radial loads on the bearing (weight of propshaft) but the propeller thrust applies an axial load to the bearing. when fitted with a reduction box, gear separation forces come into play and apply a larger radial load to what was the output bearing, with its split inner race this is not a good idea! the plain bearing fitted in its place can cope with a much larger radial force. the only axial force depends on whether the reduction gear uses helical or straight cut gears hope this helps but i know its not really relevant to the lister box, tom

 

No, not at all, interesting stuff! Ta for that! Makes sense...

 

Helical gears in the case of the lister reduction...

 

PC

[tom_c]

i knew that mechanical engineering degree would be useful for something!