T90 Tacho

[Gordonmc]

Any T90 (BMC 1.5 35h.p. Thorneycroft) owners who can help with a tachometer problem, please.

The tacho on my Hillyard never worked, so I bought a VDO unit recently. I got round to fitting it at the weekend, but when I fired the engine it either shows no revs or, after adjusting the calibration slot on the back, shoots up to 2,500 revs on tick-over. Increasing revs increases the reading slightly.

Am I right in assuming the VDO is the wrong type of unit and if so, what is the right kind? The tacho is driven from the alternator with the wire disappearing inside, presumably attached to a field winding and giving between 2.5 and 7.3 V ac.

Advice welcome.

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[steve28]

With the unit i fitted it needed an initial setup.They provided a formula and then a switch or two was set inside. Fine tuning was on a pot on the back.
mine was a durite one though.

I would expect the same for yours as they would have no way of working out pulley sizes and max rpm

steve

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