Retro-fitting a rev-counter on a diesel engine?

[Gary Fox]

To fit a rev counter on an engine without one, what is the simplest way? 12v is available. I believe there is a type with an optical sensor which can read a dab of Tippex on the crankshaft pulley. Or another which clips on an injector pipe and counts the pulses? Trying not to get involved with electronics or computers. Mucho appreciado if you have gone this route with success.

 

[DJE]

A lot of them read a feed from the alternator. I fitted an cheap replacement for a failed Volvo Penta tachometer and it was done this way. Had to calibrate it for pulley sizes and number of poles in the alternator.

 

[Gary Fox]

A lot of them read a feed from the alternator. I fitted an cheap replacement for a failed Volvo Penta tachometer and it was done this way. Had to calibrate it for pulley sizes and number of poles in the alternator.

Ok thanks. Sounds promising.Calbrating that type sounds a bit mathsy for me.

 

[DJE]

A very simple formula was provided in the instructions for the new tachometer. And guidance on which alternators have what number of poles. Nothing to it.

 

[penfold]

We fitted one of these, it's working fine. The chinglish instructions were a challenge though, a hand-held tachometer was needed as doing via a calculation was beyond our ken; once that approach was taken adjusting it was quite straightforward.

 

[Rappey]

If you cant (or wont) fit a tacho to an alternator then you can use of of these.. It has a hall effect sensor so basically a magnet it on the revolving part and the sensor counts the rpm to the digital display .
This type is often fitted to quads and similar vehicles that dont have any means of a rev counter..
Digital Green LED Tachometer RPM Speed Meter Hall Proximity Switch Sensor Strong | eBay

 

[Gary Fox]

If you cant (or wont) fit a tacho to an alternator then you can use of of these.. It has a hall effect sensor so basically a magnet it on the revolving part and the sensor counts the rpm to the digital display .
This type is often fitted to quads and similar vehicles that dont have any means of a rev counter..
Digital Green LED Tachometer RPM Speed Meter Hall Proximity Switch Sensor Strong | eBay

Thanks that is very simple. Simple is good. I will get one sent.

 

[Rappey]

You will probably need to get a disc like magnet too but they are also very cheap on ebay

 

[Leighb]

The TinyTach is the one that counts pulses on an injection pipe. Simple to fit, only calibration, AFAIR, is for the number of cylinders. Has a small digital readout and can show RPM, MAX rpm, or hours run. Not cheap but works well.

 

[Stemar]

I had a Tiny Tach on Jissel for years and it worked well. I was going to put a couple on Jazzcat, but, to coin a cliché, OMG, the price - they've more than doubled!

Nosing around the internet, I came across this, which looks interesting.
4.23￡ 8% OFF|DC 12V Waterproof Motorcycle 2 in 1 Tachometer RPM Gauge Fuel Level Gauge Meter With Digital LED Indicator Motorbike Instrument|Tachometers| - AliExpress

I wonder if it would work with one of those reed switch sensors that were mentioned on another post - if so I could definitely be tempted.

 

[johnsilver2]

As per post #2 Parts4engines provide this type of rev counter and hours meter for about £70. Looks simple to install and calibrate

 

[Gary Fox]

Thanks for the comments, a Hall effect sensor, mini magnet and digital display are on the slow boat from China, £17..

 

[Stemar]

Blatant Thread Hijack:

How important is a tachometer? It clearly isn't essential, but is a "useful to have" or a "nice to have"? Jazzcat's survived over 30 years without but since she has twin engines, I'm tempted, mainly so I can match revs better than I can by ear.

 

[DJE]

Blatant Thread Hijack:

How important is a tachometer? It clearly isn't essential, but is a "useful to have" or a "nice to have"? Jazzcat's survived over 30 years without but since she has twin engines, I'm tempted, mainly so I can match revs better than I can by ear.

You should be able to do a very good job by ear by listening to the beats.
Beat (acoustics) - Wikipedia

 

[penfold]

Listening to it is not much use to most people, as they're rubbish at guessing engine speed better than +-500 rpm. A tacho is useful with mechanically controlled diesel engines as running them above 75% is a good idea for longevity, also knowing what RPM gets what speed helps with fuel consumption estimates and detecting engine problems. With electronically controlled common rail engines these are less important, but paradoxically engine speed read-out is easier to furnish.

 

[Gary Fox]

Blatant Thread Hijack:

How important is a tachometer? It clearly isn't essential, but is a "useful to have" or a "nice to have"? Jazzcat's survived over 30 years without but since she has twin engines, I'm tempted, mainly so I can match revs better than I can by ear.

For 20 bucks including a tube of superglue it doesn't need to be essential!

 

[Stemar]

For 20 bucks including a tube of superglue it doesn't need to be essential!

 

[Bodach na mara]

I got peed off when my TinyTach stopped working after five years and found that the internal battery was not replaceable. You have to buy a new unit. And as has been said they are not cheap.