Lister Blackstone 2G - What's in the box?

[RLWP]

Another gearbox in the Lister family, sharing features with the LH150 or LM100 but with more sophistication in the details

 

At the heart is a reverse cluster made from straight cut gears:

 

 

The main input shaft engages with the first set of planet gears in the centre. You can see the main shaft on the end of the crankshaft here:

 

 

The other gears are the 2:1 drive to the camshaft on the left, and the governor gear and bob weights (top). Notice also that the lower half of the gearbox remains bolted to the engine while all the gearbox parts are removed. Also notice the oil in the bottom of the gear case which is shared with the engine sump. This is a Lister HB2

 

The gear cluster has two clutches, a band brake running on the outside for reverse, and a plate clutch in the centre locked by over centre levers:

 

 

The centre shaft in the cluster passes through the drum to this spider assembly:

 

 

The two keys in the centre and the teeth around the outside drive the boat when the forward clutch is locked.

 

In detail, we have the spider:

 

 

which drives the output shaft by the key in the bore. Onto that goes the driving plates:

 

 

The teeth engage in the inside of the reverse drum. There are two of these plates, and they are made of some kind of phenolyic material. If you have a Lister Blackstone gearbox that drags in neutral, or stalls going into reverse, it may well be these plates being distorted. They can become conical and drag all the time

 

 

Next, a cast iron plate keyed to the spider:

 

 

Then another phenolyic plate, and the end plate:

 

 

To illustrate how the clutch locks, here is the locking gear unlocked:

 

 

and locked:

 

 

On the outside of the mechanism are two levers with an adjuster on the outside. These are linked to pairs of links pointing to the centre hub.

 

In the top view, the clutch is unlocked with the hub out and the pairs of links pulling the levers in.

 

In the lower view, the clutch is locked. as the hub moves towards the clutch, the links push the levers out and the adjusters push down against the clutch pack, locking the clutch. Eventually, the hub moves so far forwards that the links over centre and start to push the hub towards the clutch instead of away from it. At this point, the clutch is engaged and the mechanism locked. It is this that holds the box in gear, not the external gear lever.

 

Building this up in the drum:

 

Spider:

 

 

Phenolyic plate:

 

 

Complete pack:

 

 

Locking mechanism and retaining nut:

 

 

Richard

 

MORE: I can't add any more images to this post, could someone post something so I can start a new post?

Edited July 30, 2014 by RLWP

[John V]

ok

[RLWP]

Thanks John

 

Passing through the reverse cluster is the output shaft, you can see it in the middle of the above view. It is locked to the output gear of the cluster

 

 

by the clutch shaft nut:

 

 

This caused me the biggest headache of this job. The nut a disc with two flats cut on it and a thread in the centre. It is then split most of the way through parallel with the end faces and has a countersunk screw fitted (you can just see this in the above view at the top). Tightening this screw pulls the two 'halves' of the nut together, locking it onto the shaft. In this case, the nut had picked up on the face of the output gear making it very hard to undo. I had to make up a special spanner and a block of steel with a keyway to hold the shaft. Much sweating and swearing and it suddenly came undone and uscrewed easily

 

This is the complete reverse cluster, forward clutch, locking gear and output shaft:

 

 

It's very nice to be able to take just a part of the gearbox away to repair in the quiet of my workshop!

 

Reassembling the gearbox. First fit the reverse band:

 

 

The reverse cluster assembly passes through this and onto the input shaft:

 

 

A bit of a fiddle, but not too bad

 

Next, the forward gear fork slips into the hub, sitting in the bottom of the box. This is held in place by a two piece cross shaft, the right hand carrying the reverse lever:

 

 

You can just see the bronze pads of the forward gear fork in the grooves of the hub. The two parts of the cross shaft are different. The right hand part passes through the case, through the lever and into the fork, the splines engaging in that:

 

The left hand part is longer and has a collar on it:

 

 

It passes through the left hand side of the box, through the collar and into the fork. This is the cross shaft, fork and reverse lever assembled, and my feet!:

 

 

That is all of the forward clutch assembly. The reverse band is operated by the lever on the shaft and a rocker:

 

 

This is shown above with the reverse band free. At the other end, the rocker pushes down on the reverse band, compressing the spring and clamping the outside of the reverse drum:

 

 

Again, this is shown with the reverse band free.

 

Pulling the external lever backwards rotates the reverse lever backwards, raising the end of the rocker:

 

 

In this position, the lever has raised the rocker right up, and has now rotated far enough for the rocker to be beginning to descend. This is how the reverse gear is locked. Again, the gearbox will stay in gear without any pressure on the external lever.

 

On the other end, the rocker has descended and is squeezing the reverse band:

 

 

After that, the rear bearing goes on and the reduction box. I don't have specific photos of that.

 

Could someone add another post please?

 

Richard

Edited July 30, 2014 by RLWP

[Mrs Tawny Owl]

Looking good so far.

[MoominPapa]

Richard, this is fantastic. What I'd really like to see is how to replace the oil seal between the main box and the reduction box. Mine (and every other one whose owner I talked to) leaks reduction box oil copiously into the main box/engine. Also, can you get bearings to fit these from a bearing supplier, rather than as Lister spares?

 

MP.

[frangar]

I had my oil seal replaced with a double lip seal on a 3G box....seems to have done the trick...it did need some machining to get it to fit the shaft though.

 

My oil was going the other way tho....

 

I agree great pics!

 

Cheers

 

Gareth

[RLWP]

I can't really comment on either of those MP as I haven't had to do either. I do regularly get bearings from suppliers for Lister boxes, although this is now getting difficult as old stocks get exhausted

 

Adjustment

 

this box is pretty easy to handle. the forward clutch is adjusted with the square headed bolts. go one flat at a time until the friction is enough to overcome the engine torque.

 

This is the forward clutch disengaged (and in reverse apparently):

 

 

And engaged:

 

 

Notice the over-centre links.

 

On the side of the box is a plate that limits the travel of the external lever:

 

 

The central notch holds the box in neutral, adjusting this is by slackening the bolts and shifting the plate. This plate is to protect the gearbox from over enthusiastic owners.

 

In forwards, the gearbox should lock the forward clutch, then the external lever just touch the end stop:

 

 

If your gearbox should jump out of forward, it may be that this stop is preventing the gearbox from locking properly

 

Reverse is the same:

 

 

This time, the stop determines how far back the external lever will go. Too short a distance and the gearbox will drop out of reverse, too great and the band brake will slip

 

I quite enjoy working with these gearboxes. They are well thought out and simple to work on. It is possible to set them up so you don't need superhuman effort to move into gear using the external lever. What any additional mechanism for remote changing might do is another matter entirely!

 

Richard

Edited July 30, 2014 by RLWP

[Timleech]

Thanks John

 

Passing through the reverse cluster is the output shaft, you can see it in the middle of the above view. It is locked to the output gear of the cluster

 

 

by the clutch shaft nut:

 

 

This caused me the biggest headache of this job. The nut a disc with two flats cut on it and a thread in the centre. It is then split most of the way through parallel with the end faces and has a countersunk screw fitted (you can just see this in the above view at the top). Tightening this screw pulls the two 'halves' of the nut together, locking it onto the shaft. In this case, the nut had picked up on the face of the output gear making it very hard to undo. I had to make up a special spanner and a block of steel with a keyway to hold the shaft. Much sweating and swearing and it suddenly came undone and uscrewed easily

Could someone add another post please?

 

Richard

 

 

This is what you needed :-

 

 

Tim

[RLWP]

I do indeed. I made one from a bit of steel tube with lugs welded on. Naturally, putting it together was a doddle

 

Richard

[neil]

A gem of an article!!!!

[RLWP]

A gem of an article!!!!

 

Thank you

 

Richard

[Tom and Bex]

Fascinating article and I think I understand a bit better how it all works and how the adjustment works now. Bookmarked for future reference when my box goes wrong!

 

Can I ask what was wrong with this box and what work you had to do to it?

[RLWP]

Distorted forward clutch plates. They can become conical, presumably due to slipping and overheating, turning them into a kind of Belleville washer. This means that the box is very hard to get out of forward. In practice, neutral disappears and the box can still be in forward when you engage reverse.

 

If the engine idle speed is set very low, the engine governor can't cope with the increased load of being in two gears at once and stalls. So, symptoms were not getting a clean neutral and stalling when going into reverse at idle

 

I had to strip the box down to the level you can see at the beginning of this thread to replace the phenolyic plates. Fortunately, the cast iron ones were fine

 

Richard

Edited August 3, 2014 by RLWP

[George94]

That was a hugely informative post, Richard. Many thanks.

 

One question. How do you know how much to adjust the two adjusting screws by? My gearbox started slipping in forward gear. I fixed the problem by tightening the two screws, but whether I have tightened them enough, too much. or just right, I can't say. The gearbox works fine, although it needs more effort to put it into forward gear than used to be the case. I fear I might have adjusted too much.

[RLWP]

That was a hugely informative post, Richard. Many thanks.

 

One question. How do you know how much to adjust the two adjusting screws by? My gearbox started slipping in forward gear. I fixed the problem by tightening the two screws, but whether I have tightened them enough, too much. or just right, I can't say. The gearbox works fine, although it needs more effort to put it into forward gear than used to be the case. I fear I might have adjusted too much.

 

In which case, I would say you have done it right! If it works fine, it's fine. It takes more effort than it did because you have put more nip onto the plates, and as you are cautious by nature, chances are you have only used the minimum amount of adjustment necessary

 

Glad you enjoyed the thread

 

Richard

[George94]

Thank you.

 

I hope your confidence is justified!

 

I'll probably tinker with it a bit more, but it's nice to know that it is not impossible to take the whole thing apart if necessary.

 

Just one other thing.

 

What is the purpose of the spring that connects the two toggles? I ask because my box doesn't have a spring.

[frangar]

Thank you.

 

I hope your confidence is justified!

 

I'll probably tinker with it a bit more, but it's nice to know that it is not impossible to take the whole thing apart if necessary.

 

Just one other thing.

 

What is the purpose of the spring that connects the two toggles? I ask because my box doesn't have a spring.

I don't think the 3G boxes as fitted to JP2 & 3's have a spring on the toggles....nor do they have the travel limiters on the plate that the gear lever rides on.

 

Cheers

 

Gareth

[George94]

That's interesting. I wonder why. Discrimination against small engines?

 

But thanks. I shall sleep more easily now.