VDO Alternator Isuzu Engine

[Robin2]

I finally got round to measuring the speed of my crankshaft and my tachometer seems to under-read by about 14%. Google has not produced any useful information about how to adjust it.

 

The model number seems to be N02 012 165.

 

In one website it suggested that you put it into calibration mode by pressing a button on the rear of the tach when switching on the ignition - but there is no button on my instrument.

 

Another website suggests there is a small potentiometer somewhere (varies between side and back) but I can't find any on mine.

 

Has anyone got any useful advice apart from leaving it alone and doing mental arithmetic?

[Ark Right]

I finally got round to measuring the speed of my crankshaft and my tachometer seems to under-read by about 14%. Google has not produced any useful information about how to adjust it.

 

The model number seems to be N02 012 165.

 

In one website it suggested that you put it into calibration mode by pressing a button on the rear of the tach when switching on the ignition - but there is no button on my instrument.

 

Another website suggests there is a small potentiometer somewhere (varies between side and back) but I can't find any on mine.

 

Has anyone got any useful advice apart from leaving it alone and doing mental arithmetic?

 

Hi I'm pretty sure there is no means of calibration on this type of alternator fed tacho on the Isuzu's, they are cheap and cheerful and accurate for enough for most users

Cheers

A

[Chalky]

I finally got round to measuring the speed of my crankshaft and my tachometer seems to under-read by about 14%. Google has not produced any useful information about how to adjust it.

 

The model number seems to be N02 012 165.

 

In one website it suggested that you put it into calibration mode by pressing a button on the rear of the tach when switching on the ignition - but there is no button on my instrument.

 

Another website suggests there is a small potentiometer somewhere (varies between side and back) but I can't find any on mine.

 

Has anyone got any useful advice apart from leaving it alone and doing mental arithmetic?

 

Since its driven off the alternator are the pulley ratios correct? The tacho (if it's like the one on my isuzu) will be micro based and drive an air cored gauge motor. Once these have been designed, tested and built they don't drift. The probability is that the unit is based off an automotive movement and accuracy would be checked during development. My bet is HMI marine used a convenient stock pulley and assumed no one would check gauge accuracy - it's not like its a sports car and we'll be red lining it!

[Sir Nibble]

What did you read the crank speed with? When was it last calibrated?

[alan_fincher]

On some alternator driver tachos, the potentiometer adjusting screw is not only recessed inside the body, and needs turning with a small screwdriver, but additionally may be covered over with a sticky label that either needs piercing or removing.

 

The actual rotation of your crankshaft can be determined with some accuracy by using most types of cheap cycle computer. There are several threads on here saying how to do that.

[Tony Brooks]

I finally got round to measuring the speed of my crankshaft and my tachometer seems to under-read by about 14%. Google has not produced any useful information about how to adjust it.

 

The model number seems to be N02 012 165.

 

In one website it suggested that you put it into calibration mode by pressing a button on the rear of the tach when switching on the ignition - but there is no button on my instrument.

 

Another website suggests there is a small potentiometer somewhere (varies between side and back) but I can't find any on mine.

 

Has anyone got any useful advice apart from leaving it alone and doing mental arithmetic?

 

 

I think my VDO has some small push button thingies that you use ti make the revvcounter reading match the engine revs on the running engine. Unfortunately my instructions are on the boat.

 

Don't know if this will help:-

 

http://uk.vdo.com/generator/www/uk/en/vdo/main/hidden/downloads/downloads_en.html?requestUri=%2Fwww%2Fuk%2Fen%2Fvdo%2Fmain%2Fhidden%2Fdownloads%2Fmarine_solutions%2Ffolder_marine_solutions_en&naviCtx=3861962

[Robin2]

What did you read the crank speed with? When was it last calibrated?

 

A multimeter that measures frequency.

 

I think my VDO has some small push button thingies that you use ti make the revvcounter reading match the engine revs on the running engine. Unfortunately my instructions are on the boat.

 

Don't know if this will help:-

 

http://uk.vdo.com/generator/www/uk/en/vdo/main/hidden/downloads/downloads_en.html?requestUri=%2Fwww%2Fuk%2Fen%2Fvdo%2Fmain%2Fhidden%2Fdownloads%2Fmarine_solutions%2Ffolder_marine_solutions_en&naviCtx=3861962

 

Thanks. Is it possible that the push button is at the bottom of a deep narrow hole and needs e.g. a very small screw driver to press it?

[Tony Brooks]

A multimeter that measures frequency.

 

 

 

Thanks. Is it possible that the push button is at the bottom of a deep narrow hole and needs e.g. a very small screw driver to press it?

 

 

I seem to remember mine was.

[Robin2]

I seem to remember mine was.

 

I shall try a cautious insertion the next fine day

[blackrose]

I finally got round to measuring the speed of my crankshaft and my tachometer seems to under-read by about 14%. Google has not produced any useful information about how to adjust it.

 

The model number seems to be N02 012 165.

 

In one website it suggested that you put it into calibration mode by pressing a button on the rear of the tach when switching on the ignition - but there is no button on my instrument.

 

Another website suggests there is a small potentiometer somewhere (varies between side and back) but I can't find any on mine.

 

Has anyone got any useful advice apart from leaving it alone and doing mental arithmetic?

 

Can you explain how you measured the crankshaft speed exactly?

 

A multimeter that measures frequency.

 

Sorry I'm confused - you mean frequency of an electrical signal? From the alternator? Doesn't any measurement have to compensate for pulley diameter, belt slip, etc?

 

I'd like to see what my crankshaft speed is, as opposed to what my revcounter says, but I think the cycle computer method is too inacurate for such a small diameter wheel.

Edited June 19, 2011 by blackrose

[Robin2]

Can you explain how you measured the crankshaft speed exactly?

 

 

 

Sorry I'm confused - you mean frequency of an electrical signal? From the alternator? Doesn't any measurement have to compensate for pulley diameter, belt slip, etc?

 

I'd like to see what my crankshaft speed is, as opposed to what my revcounter says, but I think the cycle computer method is too inacurate for such a small diameter wheel.

 

Sorry I thought your enquiry was about whether I was comparing my tachometer with another inaccurate measurement.

 

I put a bit of white tape on the crank pulley and used a photo transistor to detect light reflected from it and then measured the frequency of the amplified pulses with the multimeter. Next time I will use some chrome tape for a brighter reflection. I'm planning to do some careful fuel consumption measurements at different RPM in the near future.

[blackrose]

Sorry I thought your enquiry was about whether I was comparing my tachometer with another inaccurate measurement.

 

I put a bit of white tape on the crank pulley and used a photo transistor to detect light reflected from it and then measured the frequency of the amplified pulses with the multimeter. Next time I will use some chrome tape for a brighter reflection. I'm planning to do some careful fuel consumption measurements at different RPM in the near future.

Thanks. I think it might be a bit easier if I get hold of a strobe.

[Robin2]

Can you explain how you measured the crankshaft speed exactly?

 

 

but I think the cycle computer method is too inacurate for such a small diameter wheel.

 

I missed that bit earlier. As far as I know the cycle computer should work fine. The diameter doesn't really matter - you can read half or double (or whatever) speed so long as you understand the mathematical relationship between the pulses and the "speed" which is probably spelled out in the instructions. My concern is how to fix a magnet to the crank pulley so it wouldn't fly off like a bullet.

[paulcatchpole]

I missed that bit earlier. As far as I know the cycle computer should work fine. The diameter doesn't really matter - you can read half or double (or whatever) speed so long as you understand the mathematical relationship between the pulses and the "speed" which is probably spelled out in the instructions. My concern is how to fix a magnet to the crank pulley so it wouldn't fly off like a bullet.

 

At the speeds involved, araldite should do fine.

 

I had a cycle computer on the motorbike for a while, with a magnet attached using araldite or similar 2-pack resinous adhesive. The magnet survived some serious speed and was still there when I sold the bike.

 

PC

[blackrose]

I missed that bit earlier. As far as I know the cycle computer should work fine. The diameter doesn't really matter - you can read half or double (or whatever) speed so long as you understand the mathematical relationship between the pulses and the "speed" which is probably spelled out in the instructions. My concern is how to fix a magnet to the crank pulley so it wouldn't fly off like a bullet.

 

Yes there's the problem of fixing the magnet to the pulley but the diameter does matter (at least it did on the cycle computer I had), as you need to know the circumference and work backwards to calculate the revs because the model I had gave speed and distance but not revs. The problem is that the smaller the wheel you're using it on the less accurate it becomes because the position of the magnet on the part of the pulley you've measured becomes more critical. On a big 26" dia bicycle wheel it's much more accurate.

 

A white mark on the pulley and a strobe is a much simpler way to do it.

Edited June 19, 2011 by blackrose