Tacho drive - Lister JP

[Proper Job]

I have in my posession a very nice old Tacho that was off an Ailsa Craig RF series engine.

 

It's just about the perfect size at 4" and I'd like to somehow fit it to Ye Olde JP

 

 

It is cable driven and I still need to work out the drive ratios.

 

Any ideas on how to set up a drive for it from a JP Lister?

 

 

[RLWP]

I have seen an electric thingy on the output of the fuel pump which I presume was a generator for an electric tacho. Maybe a gearbox could be fitted there

 

Richard

[Timleech]

I have seen an electric thingy on the output of the fuel pump which I presume was a generator for an electric tacho. Maybe a gearbox could be fitted there

 

Richard

 

Tachogenerators with their matched Tachometers were the norm for a while, but there doesn't seem to have been any sort of standardisation - I've seen DC generators, 3-phase generators and impulse generators, all by Smiths and all apparently now defunct since the alternator-driven tacho became common for non-precision applications.

 

Tim

[RLWP]

I may have that tacho generator somewhere

 

Richard

[Proper Job]

I have seen an electric thingy on the output of the fuel pump which I presume was a generator for an electric tacho. Maybe a gearbox could be fitted there

 

Richard

 

I was thinking of some sort of drive from the fuel pump as well.

 

I'm going to have a play with a drill/hand held tacho and the Smiths tach at the weekend to try to find out the input drive ratios.

 

It's got a worm and wheel 90 deg gear at the rear of the gauge which is removable. That must also effect the ratio or they'd use a bevel gear for 1:1 drive(?)

[Timleech]

 

I was thinking of some sort of drive from the fuel pump as well.

 

I'm going to have a play with a drill/hand held tacho and the Smiths tach at the weekend to try to find out the input drive ratios.

 

It's got a worm and wheel 90 deg gear at the rear of the gauge which is removable. That must also effect the ratio or they'd use a bevel gear for 1:1 drive(?)

 

Is the 90 degree drive truly removable? I was looking for a replacement for a head like that, but found that the 90 degree bit was to some degree integrated into the head so couldn't simply be swapped onto another head.

 

Direction of rotation is another thing to watch out for.

 

Tim

[Proper Job]

It's removable in the sense that it comes off the rear of the gauge and all you're left with is stub and a gear wheel

 

.... and yes, it only works if rotated in one direction, so you're right that will be a factor. I hadn't thought of that

 

I'll post a piccy

[rrt2]

Look on ebay at " mechanical rev counter drive "

IIRC speedy cables will make up the drive cable that you will need.

[Proper Job]

Just had a play and the input is half engine speed. ie. 400 rpm input shows as 800 rpm on the gauge

 

The 90 deg' gear is 1:1

 

 

 

Driven off the fuel pump could be an option? if it's the right rotation

[magnetman]

could you drive it off the prop shaft? if you have a 2:1 reduction that is. maybe some sort of friction wheel would do it

the thing would be easily rotateable as well so rotation direction wouldn't matter you just mount the wheel the way round that you want it. obviously the wheel would need to be the same dia as the shaft. I have no idea if this would work. It would also bring the rev counter closer to the steering position which may be quite a big advantage.

This does have the weakness of not giving you rpm when in neutral though, which may actually be what you want to see in the first place

 

You can use a bike computer for that not sure its that 'vintage' though

Its certainly a very handsome instrument

(The one pictured in the original post I mean)

I suppose the friction wheel thing could be set up at the front of the engine on the crankshaft if it extends far enough. then use a wheel twice the diameter of the shaft to get the 2:1 reduction.

Edited December 5, 2014 by magnetman

[RLWP]

Fuel pump is looking ideal, Steve

 

Richard

[Proper Job]

Fuel pump is looking ideal, Steve

 

Richard

 

That's what I'm reckoning. Just which way everything rotates now

[by'eck]

Just found this thread although have already sent PM to PJ.

 

Don't know if this thread helps although I'm guessing you have the plunger not gear type water pump (assuming JPM) whose shaft was used to provide anti-clock tacho drive at engine rpm. BTW if you take the original JPM route I have some parts left over after fitting mine including new drive cable.

 

RLWP is well up to speed on original tacho drive as well

 

ETA: having read the whole thread the injection pump take off seems a possibility although I believe MPS fit modern Jabsco impeller pumps driven directly from the other end of the injection pump drive, so that may be a option. Issues will be getting drive rotation to suit and machining suitable drive adapter to match cable nut and the fish tail drive to cable inner. As mentioned I have a standard NOS cable with 3/4" BSC nut at engine end and the larger diameter fine thread nut and square drive at instrument end which looks like a match to your tacho.

Edited December 6, 2014 by by'eck