Rev counter calibration

[jagwit]

Is it possible to calibrate the rev counter (tacho)? It seems to me that the unit in the car I'm working on overreads by at least 500rpm.

[christopher storey]

Yes, but it depends which type of instrument you are working on. What is the car and its year ? If the tacho is an impulse type, such as on your series 3, then there will be a potentiometer within the case which can be used to vary the readings. However, if it is out of trim it may be that the readings vary with temperature. This is a very common fault and usually is the result of a failed thermistor in the tacho. You will find various circuit diagrams on the internet and it is then usually possible to replace the affected component


PS if it overreads by 500 rpm at all speeds, then the fault is probably not electrical but mechanical in that the needle has become twisted on the shaft

[jagwit]

Thank you Christopher

I'll have a look at it in October hopefully. Current owner hardly ever consults his instruments anyway and won't be bothered even if he knew. For me its important to get it right.