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Thread: Tachometer reads high when engine compartment heats up

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    Tachometer reads high when engine compartment heats up

    My tach when first going reads steady and right RPM, when engine warms up, tach reads high, under dash feels ambient temp, took out of dash, set on seat and same thing, read fine until engine starts to show temp, it seems as engine hotter tach gets higher, oh, original distributor and other parts. any thoughts? Thanks, Jay '65 3000

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    Jedi Knight dougie's Avatar
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    Re: Tachometer reads high when engine compartment heats up

    Check the coil, I've had similiar issues with the tach on my BJ8 when the coil got hot.
    Dougie
    '65 BJ8 3000 MKIII GN.29
    '57 100-SIX MM Vintage Racer GN.1 #414
    Team Healey PDX

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    Obi Wan Patrick67BJ8's Avatar
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    Re: Tachometer reads high when engine compartment heats up

    My Tach was the exact opposite. I ended up having to have it rebuilt by Nisonger and they upgraded it to handle pertronix and other performance ignitions and now it works great. My ignition is stock except for pertronix and Bosch blue coil.
    Patrick
    '67 Metallic Golden Beige/Red
    Owned since '72

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    Luke Skywalker RAC68's Avatar
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    Re: Tachometer reads high when engine compartment heats up

    Hi Jay,

    Your's is not a unique experience with the Smiths Tachometer as there is an issue with an internal leaking capacitor that has caused issues as you described. I believe it was an article by Jim Werner that I followed to replace the fractured .22uf Capacitor and recalibrate the tachometer after the quick and easy parts replacement. The replacement electronic component was no more then $1.50 and the unit has remained accurate and stable for the past decade.

    I suggest you take a look at the 2004 British Car Forum post made by "Shorn" describing his Smiths Electronic tachometer issues and resolution.

    Sorry, but I seem to have misplaced the article I followed, however, Frank Filangeri has an article "BJ8 Tachometer Reading High" posted on John Sims Healey6 site (www.healey6.com/Technical/Werner/BJ8%20Tachometer%20Reads%20High.pdf) that goes through describes the process. Also, there are 2 other articles that address the rebuilding and technology of the Smiths Electronic Tachometer.

    All the best,
    Ray(64BJ8P1)
    Last edited by RAC68; 06-15-2018 at 05:01 PM.

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