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Old 02-27-2014
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Adapting an automobile tachometer

Hy
The tachometer on the motor panel of my volvo 2030 engine dont return to zero after switching out the motor.
A friend with a similar volvo installed an automobile tachometer.
The problem is that the readings do not correspond to the real rpm.
Any idea of how to adapt such a tacho?
Thanks in advance

Saludos
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Old 02-27-2014
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Re: Adapting an automobile tachometer

Gas engine and diesel engine tachs are not interchangeable. Sorry, you're going to have to bite the bullet on this one.
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Old 02-27-2014
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Re: Adapting an automobile tachometer

not to say obvious things, but have you checked the wiring? usually that means bad ground.

tachs are tachs.... auto or otherwise. just have to calibrate it. need more info to get in deeper
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Old 02-27-2014
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Re: Adapting an automobile tachometer

Tachs can be mechanical (becoming rarer but there are still a few about) or electronic.

Electronic tachs can be driven of off the ignition pulse (won’t work with diesel) or off an electronic trigger.

The trigger can pulse at engine RPM (Crankshaft trigger), half engine RPM (camshaft or sometimes distributor trigger) or sometimes some other shaft/speed.

The tach pulse can be send directly or modified via the ECU.

Bottom line is that you need to know what you are dealing with and match the tach input for the tach you are using.

edit: There are also different types of trigger. Sorry!

The easy way is to use the correct tach.
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Re: Adapting an automobile tachometer

oh yeah, i guess i should been more specific... what Geoff54 said knowing what kind of trigger you have then u can get whatever tach matches, but need more info.

think urs is an alternator type? have to set the settings on new tach to match. have to know crankshaft and alt pulley diameter then ref. instructions. most have dipswitch or selector switch
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Old 02-27-2014
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Re: Adapting an automobile tachometer

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Originally Posted by Ulfilas View Post
Hy
The tachometer on the motor panel of my volvo 2030 engine dont return to zero after switching out the motor.
A friend with a similar volvo installed an automobile tachometer.
The problem is that the readings do not correspond to the real rpm.
Any idea of how to adapt such a tacho?
Thanks in advance

Saludos
The MD2030 uses an alternator sensed tachometer. They are often called "diesel tachs". They use the AC pulses from the alt for their signal and require calibration to the alt. Many companies make replacement alt sensed tachs..
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Re: Adapting an automobile tachometer

Maine, how hard is it to add a tach to an engine? My Universal 5416 doesn't have one, and I'd really like to get a better feel for the engine speed.
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Re: Adapting an automobile tachometer

when you say it does not return to zero.. does it just stay where it is, or does it drop to a point close to zero and stay there?

It might be worth taking it apart and doing some cleaning. Tachs are a relatively simple device with some very lightweight parts. a little bit of corrosion or dirt could easily stop the needle
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Re: Adapting an automobile tachometer

Auto Meter ## 2888 diesel tach. Comes with strap on sensor for alternator.and instructions to adj for correct rpm. Says that it might not zero whenn off.
IIRC,eBay prides as low as $nintey nine.I ndeed one too, so looking hard.this one is external deck mount, in it,s own "can", but could be adapted to flush surface?
Some work off injector pulse, buthaven't found one for three cylinder
t
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Old 02-28-2014
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Re: Adapting an automobile tachometer

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Originally Posted by jimgo View Post
Maine, how hard is it to add a tach to an engine? My Universal 5416 doesn't have one, and I'd really like to get a better feel for the engine speed.
You just need an alt with an "AC Tap" or stator tap and a diesel type tachometer. Any alt show can re-wire your alt to have a stator tap for an alt.. You will also need a digital photo tach for calibration to your engine RPM. Not difficult, just requires some patience..
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