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Hi All,

I've been trying to fix my under-reading tachometer - it reads 4,000rpm when it really is 5,000rpm. Lower down the rev range it seems better and the speedo is pretty good compared with GPS.

I've swapped over to a refurbed/calibrated gauge and its still no better. I've checked the cable and that seems OK, the inner turns freely and doesn't seem worn at the ends.

Is there anything else I could check or change?

Thanks Darren

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11 minutes ago, DRD said:

Hi All,

I've been trying to fix my under-reading tachometer - it reads 4,000rpm when it really is 5,000rpm. Lower down the rev range it seems better and the speedo is pretty good compared with GPS.

I've swapped over to a refurbed/calibrated gauge and its still no better. I've checked the cable and that seems OK, the inner turns freely and doesn't seem worn at the ends.

Is there anything else I could check or change?

Thanks Darren

Hi Darren

Just out of interest how are you measuring the true RPM?

Kevin

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Hi Darren,

The tacho drive cable is a direct take off from the distributor so unless you have the wrong drive gear in the distributor there really is nothing that can go wrong with it other than a wrongly calibrated tacho or worn cable and as you fitted a refurbed gauge the former seems unlikely. Also unlikely that you have the wrong drive gear in the distributor as I don't think any other Triumphs had a mechanical drive tachometer.  I can only suggest a new cable albeit I don't think that is the problem as any wear in that would be obvious at the gauge with readings all over the place / bouncy needle.

Hopefully someone else will have had the problem and have the solution to hand.

Derek.

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11 hours ago, boxofbits said:

Hi Darren

Just out of interest how are you measuring the true RPM?

Kevin

Hi Kevin - this was done by measuring the firing of the ignition whilst on a rolling road.

The odd thing is that at 3,000 rpm its seems fine as the speed and revs are all consistent.

Cheers

Darren

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Hi Darren,

               now for a proper reply from me - doh!!

As the tacho is capable of reading correctly at the lower speeds I would suggest that the internals of the gauge need adjustment.

If the gap (or magnetism ) changes then the linearity will change.

 

Roger

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Open your wallet and say ‘help your self’ and go chronometric .....

completely period and quite accurate compared to the magnetic flux unit currently fitted 

 

http://chronometrics.co.uk/html/tachometers.html

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