Moss Motors, Ltd

-1966 bj8 -i just started it and the tach is reading twice what it should -at idle it reads 2500 and with low revs reads 4500-5000

any ideas?

thanks-dave m

I assume it's an electronic tach, of the Smiths/Jaeger type and not a modern replacement. In which case this is somewhat normal as the electronic components inside the unit age. Particularly, this is true of capacitors, which become electrically leaky in addition to shifting in value. This really upsets the operation of the tach circuit.

This website: http://www.classictiger.com/techtips/motach.html has a very good overview of the tach design. If you are competant with a soldering iron, they are quite easily reconditioned with a handful of modern, inexpensive components. Your tach is at least indicating when the engine is running, so the transistors (which are hard to find replacements for) are still good. That makes repair fairly straigntforward. I've done this to a couple of instruments for my '67 MGB, including a decent recalibration and was happy with the results.

Cheers,

Ed

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I want my MGB

thanks for the reply ed- that sounds a bit out of my expertise so i guess i might just have to make do

dave

As an Electronics teacher in a technical high school, this would be a job that I'd take on with my students. It really NOT that complicated for someone with a bit of experience.

Perhaps you can call tech schools in your area and ask. Make sure that you tell them you have the schematic and calibration procedure!  

OH..WAIT! I just noticed this post originated in August! Well, I hope everything worked out OK  

 

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

'68 Sprite 1275
'76 Midget 1500