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Swapping a Blackstone reduction box over


Liam

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Well my couple of years of searching has paid off and I have managed to acquire a Lister Blackstone gearbox with a 2:1 reduction box attached, without having to sacrifice a limb to pay for it.


The plan is to replace Ariel's current 3:1 reduction box with the 'new' 2:1 box. I'd then have a complete 3:1 gearbox as a spare.

Hopefully it should be fairly straight forward but I'd like to ask if there's anything I should look out for or keep in mind during the op?

Thanks
Liam


 

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1 hour ago, frangar said:

You might find the height of the output flange is higher on the 2:1 box as the gear train is smaller in diameter...I might be wrong....

 

Id also check the state of the gear cluster & clutch plates..both forward & reverse...much easier to sort while on the bench! 

If there is a difference in height, how much would this be?

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2 minutes ago, Liam said:

If there is a difference in height, how much would this be?

I’m honestly not sure....but if the reduction gears are a different size I’m guessing the centres might be different so the output flange will be different....I can measure my 2:1 3G (lister JP2) reduction box this evening if it helps. 

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3 minutes ago, Liam said:

If you could do that later it'd be much appreciated. Would rotation also be the same?

No probs. As it’s just a change of gear size the rotation will be the same. I am assuming that the box is more or less the same as my JP box. I think all the “G” series are similar. 

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1 hour ago, RLWP said:

It is easier to swap the reduction box and output gear than to swap the whole gearbox

I had a heap of fun getting the output gear off the gear cluster shaft.....are the 2:1 & 3:1 output gears the same....plus is it a good idea to mix gears that haven’t been worn together?? 

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2 hours ago, frangar said:

I had a heap of fun getting the output gear off the gear cluster shaft.....are the 2:1 & 3:1 output gears the same....plus is it a good idea to mix gears that haven’t been worn together?? 

I'd want to keep a pair of gears together, there's no guarantee the tooth profiles are the same. On reflection, I'd swap the clutch pack, shaft and rear bearing from one box to the other. That would save having to pull the gear

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9 hours ago, frangar said:

You might find the height of the output flange is higher on the 2:1 box as the gear train is smaller in diameter...I might be wrong....

 

In "Sickle" we have a while back taken out an HA3 with a 2:1 reduction, and in place put in an HA2 with 3:1 reduction.

 

The position of the coupling to the shaft appeared to have been unaltered, so I'm fairly confident this will not arise.

I assume there is a good chance that "Ariel", (like "Sickle"),  has a prop-shaft with spider joints in it?  If so any small change would surely not matter?

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Yes there's plenty of wiggle room on the shaft, there's a UJ just before the flange to the gearbox and another one further along the line towards the prop.

 

It's attempting to remove the reduction box from the gearbox. Having not done it before I'm not sure what I'll find. I'm sure I have a manual somewhere which I'll try to find to see what's what.

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1 hour ago, alan_fincher said:

 

In "Sickle" we have a while back taken out an HA3 with a 2:1 reduction, and in place put in an HA2 with 3:1 reduction.

 

The position of the coupling to the shaft appeared to have been unaltered, so I'm fairly confident this will not arise.

I assume there is a good chance that "Ariel", (like "Sickle"),  has a prop-shaft with spider joints in it?  If so any small change would surely not matter?

 Oh that's interesting....I assumed as the output gear is bigger on the 3:1 box then the drive flange would be a different height.

 

Anyhow on my reduction box which is 2:1 fitted to a 3G box as per a JP2 the distance between the centres of the input/output gears is 6 inches.

 

i separated my reduction box from the reversing box by undoing all the fixing dowel nuts...including those that are accessible by removing the reversing box cover plate and using a big pry bar between the two boxes....you will need to support the reduction box as it slides.....and beware it's really heavy!

 

Make sure when you refit it that it's perfectly parallel...there should be spacers on the dowels....mine was missing these so I needed to use washers as packing....if it's out not only are you putting strain on the gears but oil will leak between the joint. There is a rubber o ring on mine...I made one to fit as I couldn't find one the right size.

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4 hours ago, Liam said:

I've no experience about doing this but it sounds as though it's more complicated than I imagined? 

If what you bought is an aluminium cased gearbox, the case is the same as your current one. The reduction box comes off the back very easily, and with the top off the box you can remove the clutch pack, rear bearing and output gear. Swap them with the ones from the 2:1

 

The alternative is to jack the back of the engine up and pull the whole gearbox - which is quite heavy

 

Richard

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On 19/09/2018 at 08:21, Liam said:

If there is a difference in height, how much would this be?

No difference in height, the change from 3:1 to 2:1 is just a change in ratio of the gear. I have in the past converted a 3:1 box to 2:1 with some custom gears.

22 hours ago, frangar said:

I had a heap of fun getting the output gear off the gear cluster shaft.....are the 2:1 & 3:1 output gears the same....plus is it a good idea to mix gears that haven’t been worn together?? 

Some come off easy (pull off with your hand) other are like they are welded on.

 

The gearbox output gear/reduction input are different between 2:1 and 3:1 (Number of teeth)

 

Good practice would be that you do not mix gears that have been used/worn. as much as they will work they will have bedded into the gear they were originally mated to and in most cases are noisy if swapped around.

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15 minutes ago, martyn 1 said:

No difference in height, the change from 3:1 to 2:1 is just a change in ratio of the gear. I have in the past converted a 3:1 box to 2:1 with some custom gears.

 

Well you learn something new every day! 

 

Thanks for that. I guess I just assumed only the output gear changed....I’ll go and stand in the corner for a bit!!! Whoops!!

 

 

Edited by frangar
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  • 3 weeks later...

Piece of cake liam to swap reduction boxes over.as richard says,far easier than swapping whole gearbox.just make sure you have room to pull reduction box off and make sure the leather seal is good condition or you will introduce gear oil into the engine

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