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Tachometer not working following ignition upgrade

msgt

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I have just upgraded my 1964 BJ8 Phase 2 with a CSI unit - this was a bit fiddly but went well and the engine is a lot easier to start and runs very nicely.

However - the tachometer does not work - I have tried reconnecting the tachometer wire but without success.

The car is positive ground and, for some reason, the tachometer is labelled -ive ground - and was wired up aftermarket - before I start troubleshooting and replacing the -ive ground tach with a +ive ground one - has anybody seen this before?

Thanks

Mark
 

Jerry

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Some have said the electronic ignition does cause change in the tach. Go to Healey6.com and look under technical and electrical. There are articles about changing the the tach. I think one said take one loop out of the sensor wire on the back of the tach for electronic ignition.
Jerry
 
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On the AHEXP forum, someone posted an old doc for wiring a Smiths tach with a Pertronix; it showed one loop around the pickup on the tach (try wiring it in both directions). I have a Pertronix on my BJ8, and the tach works OK up to about 4,500RPM, where it bounces like crazy (but I rarely rev that high). Both points and electronic ignitions send pulses and I've always wondered why the issue with electonics; maybe because the electronics output more of a square wave, possibly with a higher voltage.
 
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msgt

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Tachometer now working - thanks Bob and Jerry

I did not have original wiring.

The eventual solution was to revert back to the original wiring and take out a loop so that the white wire passes through the pickup only once - I had also upgraded the coil to a Lucas DLB 105 and it seems that the pulse was too powerful when the loop at the back of the tachometer was in place.

I followed links from Healey6.com and AHEXP and found the solution under Pertronix support - I also found the Gentleman's Guide useful and an interesting read.

Pertronix Support

Gentleman's Guide to Smiths Tachometers

Thanks

Mark
 

Bill Young

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Mark

Good to see you have your tachometer working. I had confirmed that the Smith's RVI tachometer will work with the Pertronix (or equivalent) unit so I knew you would find the problem. Fortunately, your tachometer was not damaged. I wrote a couple of articles for the HEALEY MARQUE magazine last year on how this tachometer works. Perhaps this is a little bit more information than you need, however, it is interesting to know how these tachometers were designed back in the day of transistors.
 

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Jerry

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Bill,
thanks for writing the articles and sharing. I have an early BJ8 with I have converted to negative ground. The later models you just switch the green wire and the long brown thing (don't know the electronic name). The early unit does not have a green wire. Have you any hints for that unit?
 

GregW

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Jerry, the earlier tachs were mechanical so no green wire, no looped white wire.
 

Jerry

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Greg, it is a BJ8, all had electronic tachs. But the early ones had a different inside than the later.
 
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