Tachometer sensor options?

skyflyer

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I have older style magnetic sensor that picks up flywheel teeth and a corresponding tachometer gauge. The sensor has failed and a replacement is upwards of £150
Am I better off buying a new gauge of the other type (much less than £150) and wiring to the alternator? What are advantages or disadvantages of the two different types?
 

pvb

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I have older style magnetic sensor that picks up flywheel teeth and a corresponding tachometer gauge. The sensor has failed and a replacement is upwards of £150
Am I better off buying a new gauge of the other type (much less than £150) and wiring to the alternator? What are advantages or disadvantages of the two different types?

I'd start by checking the wiring carefully, unless you're sure the sensor has failed (including checking that there's a 12v feed to the tacho). If you're confident it's the sensor, it's only a basic flywheel sensor (as found in cars), so you might be able to cobble something together using a sensor from a scrapyard.

If you buy a new tacho which runs off the alternator, you'll need to calibrate it in some way, perhaps by borrowing a strobe tacho. There are no particular advantages or disadvantages of either type, they're just tachos.
 

Amulet

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Consider a "Tiny Tach". Sensor clamps on an injector line. I've had one for years. Bit puzzled cos I see them priced at about £75. Sure I payed much less. Dead simple though, and easy to install.
 

skyflyer

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I don't see the point in a solution that requires a different shape/sized gauge when i can simply buy the same size gauge of the different type and fit it in three minutes in the old hole!

So the least pricey and simplest solution is to use an alternator sensed tacho gauge. I have a laser rpm device to accurately calibrate it.

I guess the next problem is to work out relationship between alternator waveform and the engine rpm - presumably a function of pulley sizes etc. Dies one size fit all or do you have to buy a specific gauge for a specific ratio I wonder?
 

pvb

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I guess the next problem is to work out relationship between alternator waveform and the engine rpm - presumably a function of pulley sizes etc. Dies one size fit all or do you have to buy a specific gauge for a specific ratio I wonder?

There will usually be a calibration adjustment facility on the back of the tacho.
 

Cuan

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I don't see the point in a solution that requires a different shape/sized gauge when i can simply buy the same size gauge of the different type and fit it in three minutes in the old hole!

So the least pricey and simplest solution is to use an alternator sensed tacho gauge. I have a laser rpm device to accurately calibrate it.

I guess the next problem is to work out relationship between alternator waveform and the engine rpm - presumably a function of pulley sizes etc. Dies one size fit all or do you have to buy a specific gauge for a specific ratio I wonder?

There will be a coarse adjustment, based on the pulley sizes and alternator - see here for details www.fwmurphy.com/uploaded/documents/pdfs/.../00-02-0258.pdf. this is for Murphyy tachometers, but the same principals will apply to others (e.g. Faria), and then you will need to make a fine adjustment using a strobe
 
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