DRD Posted July 2, 2019 Report Share Posted July 2, 2019 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 Quote Link to post Share on other sites
boxofbits Posted July 2, 2019 Report Share Posted July 2, 2019 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 Quote Link to post Share on other sites
RogerH Posted July 3, 2019 Report Share Posted July 3, 2019 (edited) oops - my reply was for a dodgy speedo Roger Edited July 3, 2019 by RogerH Quote Link to post Share on other sites
saffrontr Posted July 3, 2019 Report Share Posted July 3, 2019 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. Quote Link to post Share on other sites
DRD Posted July 3, 2019 Author Report Share Posted July 3, 2019 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 Quote Link to post Share on other sites
RogerH Posted July 3, 2019 Report Share Posted July 3, 2019 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 Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 3, 2019 Report Share Posted July 3, 2019 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 Quote Link to post Share on other sites
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