RPM sensor and display fitted

[Refueler]

Some time ago - I posted about a Tacho system that looked intriguing.

Alternator Sensor :

Diesel Engine RPM Tacho Sensor UNIVERSAL For Vehicle Truck Boat Yacht Waterpoof | eBay

The sensor is basically zip-tied to alternator case and it pulses based on rotation of the stator ..

52mm Car Marine Tachometer 0-4000RPM Diesel Engine Tacho Gauge With Hour Meter | eBay

My engine is a Perkins 4-107 and the mechanical drive tacho outer sleeve to cable is there - but the inner is missing and no mechanical display. I considered obtaining new drive cable / fittings and a display - but when I saw the above and saw youtube video ... it was obviously cheaper and better.

The Display needs just a smidgeon less than 52mm hole to fit .. wiring is simple and calibration simply by shorting a white wire to enable pulse detection on the display. The sensor is similarly setup if needed by a white wire shorted and held to scroll through the pulse settings.

I thought I would just install and see what factory gave ... idle appeared to be ok at about 500rpm ... but on increasing throttle it quickly rose to 3000+ at half throttle ... so I elected to calibrate display .... shorted the white wire .. started engine, throttle at estimated 1000rpm .... disconnect white wire etc.

Now idle still about 450 - 500rpm ... full throttle (no load) put needle to the max of 4000rpm ....

It appears that I may need to calibrate sensor and then display again. Next time I will remember to take my LED Tacho to set engine exactly 1000rpm !!

BUT ... the 4-107 is stated to 4000rpm ... possible that my reading is real ...

Recc'd ? Yes certainly .... far more convenient to mount where you want instead of the cable driven mechanical ...

 

[penfold]

We fitted one of these, but the effect is the same; we calibrated it with one of those cheap laser tachometers, a square of the supplied reflective tape on the flywheel worked very well indeed.

 

[Refueler]

Just spent an hour playing with it ... instructions say White wire touch neg for 3 secs and then its in setting mode ... etc.

I set the sensor and then display showed about 200rpm when engine was LED Tach'd at 1000rpm.

I could not get display to adjust up or down as per instructions ... I redid the wiring ... and still no change.

Finally I added a length of wire to each .. white and negative so I could sit in cockpit better and observe display.

Purely by accident I found that instructions had missed out a few words ! Not unusual when Chinese translated.

Started engine ... touch white to neg for 3 seconds ... then touch again and HOLD it there ... nothing happens for ages then needle starts moving up .... but soon starts to shoot up ... so its hold - get needle start going up ... before it gets too fast and shoots past actual rpm point disconnect and quickly touch again - which starts it going down - discon and touch again - so its back to slow increase ... repeat doing it in stages till correct rpm shown.

I ended up with :

Display (idle) 600 LED Hand tacho 620
Display (1000 rpm) LED Hand tacho 1030

I did open to full and display showed ~3800 ... but I did not hand tacho ... as it means climbing in over open engine box to tacho the crankshaft pulley.

Some may wish to play more and get more accurate - but for me - its good enough - the display is in 100 rpm steps ... so its basically a guide rather than exact tool.

 

[Refueler]

Review after having used for reasonable period ...

I wish I had fitted one earlier. It has proved reliable and sufficiently accurate enough when compared to LED strobe tacho.

In fact I plan to fit one to my new addition to the fleet ... which has a 2GM23 ... but would like a square black display surround to match the existing .... hard to find. Solution may be to 3D print a surround and set the round display in.