Tachometer

[Robotstar5]

The dynamos on all the old tractors had a cable drive for the tacho, the later models ran the cable off a drive on the block.
Electric tacho ran off a tacho contact on the alternator, or on a spark ignition they can work off the coil, just make sure your tacho is for 4/8/12 clyinder or 3/6 clyinder whichever you have.
I would be converting the tractor to negitive earth, as you might have problems with getting a modern radio or other accessorys to work, its usually only a matter of polarising the regulator for the negitive earth and swopping the battery terminals.

What type of tractor is it?
Im sure the fergie 20 ran cable drive off the dynamo and the 35 ran a cable off the back of the block

It's a little grey fergie, I've started a thread about it here

The original tacho ran off a rubber wheel rubbing on the fan belt - see pic in first post.

No sign of any drive on the back of the dynamo

It's not charging at the moment so if the dynamo is kaput I will fit an alternator and swap to negative earth

 

[sloderby]

Shouldn't the bolt on the dynamo be inside the slot in the adjustment brace arm?
Maybe it just needed a little bit more adjustment to fit the stretched/oversize belt - must be a honest fergie as that's just what a farmer would do!

 

[Robotstar5]

Shouldn't the bolt on the dynamo be inside the slot in the adjustment brace arm?
Maybe it just needed a little bit more adjustment to fit the stretched/oversize belt - must be a honest fergie as that's just what a farmer would do!

There were a couple of "farmer fixes" I covered in my thread - here

 

[Greeves246]

Try

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[indy4x]

If you can find a rev counter off an old Triumph or MG sports car they are all triggered from the LT wire on the distributor

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[Robotstar5]

Try

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There's some nice ones on there, with nice prices too, it looks like most car/bike types are all 6000 rpm upwards, I only need 3000 rpm max.

 

[Jack_K]

There's some nice ones on there, with nice prices too, it looks like most car/bike types are all 6000 rpm upwards, I only need 3000 rpm max.

a VDO 333035004 is an example of a suitable tacho as long as it doesn't need to match the age of the tractor.

 

[bert]

Look up a rev counter kit for a mk1 mini. They has pos earth dynamos

 

[Ubique]

It's a little grey fergie, I've started a thread about it here

The original tacho ran off a rubber wheel rubbing on the fan belt - see pic in first post.

No sign of any drive on the back of the dynamo

View attachment 333179

It's not charging at the moment so if the dynamo is kaput I will fit an alternator and swap to negative earth

If that's yours, I'm not suprised it's not charging, the drive belt is too long, so much so that the tensioning bolt is not even in the bracket.

 

[Robotstar5]

If that's yours, I'm not suprised it's not charging, the drive belt is too long, so much so that the tensioning bolt is not even in the bracket.

If you'd seen my thread, the fan belt has been replaced and bolt now fitted correctly

 

[Stueeee]

All the rev counter drive dynamos I've seen have a 4:1 gearbox. Being as the dynamo pulley is smaller than the crank pulley, the matching mechanical rev counters need to be 3:1 or 3.125:1. Likely to be a bit spendy as most of these rev counters were OE on cars like the Frogeye Sprite. One of the other issues is that most of the rev counter drive Lucas dynamos were based on the earlier C39 design which is only good for about 18A output IIRC. I have grafted a 4:1MZ motorbike RC gearbox onto the back of a Lucas C40L dynamo which has a higher -but not high by today's standards- current output to drive the rev counter on one of my cars.

 

[Robotstar5]

I think I may try some like this looks like it uses inductive coupling off one of the plug leads.

 

[Stueeee]

I think I may try some like this looks like it uses inductive coupling off one of the plug leads.

Looks like a simple low cost solution