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Looking for a Diesel Tachometer


HoSS
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You would think that would be fairly easy, but i have some specific requirements thats making the search a little difficult.

- Black faced with White lettering, like the classic Smiths or Mocal models.

- Diesel, alternator 'W' feed type

- max at 6000 rpm (would tolerate 8k)

- preferable black bezel, not chrome.

I've tried the usual places like demontweeks & ebay, but no joy. I found some bling chinese stuff, but it doesnt match the other gauges on my dash.

Any ideas for a source?

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My query is around how do you ensure the tach indicates crankshaft rpm rather than alternator rpm?

The query is based on the 'being awkward' suggestion that the alternator may well rotate faster than the crankshaft.

I've looked at the linked website but cannot see a readily available answer.

Cheers.

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my assumption is that the 'W' output tachos have a calibration potentiometer, or multiplier switch. This VDO one seems to have just that.

mmmgemini thanks, but croytec seem to be putting too much markup on that. $79 from the US, or 106 quid from them. Still cheaper even with shipping.

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I have a VDO tacho fitted. Slight word of advice, I believe they come in 6k and 8k versions. Something to watch out for.

As I recall, the unit is fitted with some DIP switches for coarse calibration and a pot for fine calibration. This may have changed, I fitted mine about 8 years ago. I set it up using tick-over and throttle limit, so it could definitely do with improvement. I keep meaning to borrow a shaft tacho from work and put it on the crank.

Luke

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My query is around how do you ensure the tach indicates crankshaft rpm rather than alternator rpm?

The query is based on the 'being awkward' suggestion that the alternator may well rotate faster than the crankshaft.

I've looked at the linked website but cannot see a readily available answer.

Cheers.

It's more awkward than you think, since even if you know the alternator 'gearing' you don't necessarily know how many poles the alternator has....

However you could always RTFM ;)

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When I swapped alternator pulleys from the large to small one. I queried did I need to re-set the tachometer.

I was told it would make no differenvce.

It was all explained to me by my auto electrician. I didn't understand why at the time and still don't understand now.....

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When I swapped alternator pulleys from the large to small one. I queried did I need to re-set the tachometer.

I was told it would make no differenvce.

It was all explained to me by my auto electrician. I didn't understand why at the time and still don't understand now.....

The only reason it could make no difference is if the gauge was particularly innacurate.

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Interesting as it made no difference. Aparently the information came from Vauxhaul......

The larger pulley would run the alternator 20% slower than the small pulley, so the gauge reading should have changed by about that much. So unless the number of poles on the alternator changed at the same time then the reading should have changed.

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The larger pulley would run the alternator 20% slower than the small pulley, so the gauge reading should have changed by about that much. So unless the number of poles on the alternator changed at the same time then the reading should have changed.

All I can say is that

a I was told it would make no difference

b it made no difference.

c aparently Vauxhaul do it all the time.

Although I can wire a car successfully I have no idea how electrics or electronics work, I have to believe other people.

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I've looked at the linked website but cannot see a readily available answer.

It's more awkward than you think, since even if you know the alternator 'gearing' you don't necessarily know how many poles the alternator has....

However you could always RTFM ;)

You found the instructions for me, thankyou :-)

Let's hope HoSS has access to the necessary 'reference tachometer'.

Although it doesn't meet the display criteria requested in this case, the Tiny-Tach may be suitable as a reference tachometer, although if that is all that is required, searching for 'optical tachometer' on ebay will produce more cost effective possibilities.

Tiny-Tach Diesel instructions here.

Cheers.

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Thanks for all the input guys, yes i will work out a way to calibrate it.

The real question which has been answered was about finding one that matched the dash (no its not a LR) but that VDO is perfect.

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I set mine to indicate the correct idle speed (was a crate engine so knew it should be about right) and it was more than close enough all through the range for my TGV.

As David suggests, the £8 ebay optical tachos are suprisingly good - I have one in the workshop.

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