Well since no one answered my previous post I figured I wasn't asking the right question or it sounded so dumb no one wanted to answer. I am not a mechanic but am trying to save some money, so excuse me if I sound stupid. It may be that the wise move would be to take it to a mechanic but I want to ask one more "stupid" question. Can any tachometer work on any motor? If any tach can work, and I'm hooking up the right wires, why wouldn't the tach work?
Haw can I trouble shoot a non-working tach
. Any help would be appreciated even if its telling me to take it to someone who knows.
Howdy,
Welcome aboard!
A tachometer is pretty much a simple (voltage) pulse counter that displays in RPM.
There's usually a switch on the back so you can tell it if the engine has 4, 6 or 8 cyl etc and if 2 stroke etc.
Can any tachometer work on any motor?
Essentially, YES. To display accurately, it would need to be switchable or selectable to match the number of cyls the engine has (even/odd/2cy/4cy etc)
If any tach can work, and I'm hooking up the right wires, why wouldn't the tach work?
Well, the obvious possibilities include a defective tach or it's connected wrong.
Haw can I trouble shoot a non-working tach
This could be problematic if you cannot disassemble the instrument. Because if it's defective (inside) there's no easy way to fix what's wrong.
It probably wouldn't be cost effective to "take it to someone" because most shops would want at least 1/2 to 1 hour to troubleshoot anything. (It'd be cheaper to just buy another tach)
If you don't have a diagram to check connections,
Here's a good guide
http://www.foreandaftmarine.com/ob tack guide.htm
If I were going to test one, I would use an accurate signal generator capable of producing square waves. Most audio generators would probably work well....
OTOH, I did a little reading on bench checking a tach and found a rather simple way to test one.
Most cheap battery chargers produce somewhat unfiltered pulsating DC. (Battery charger manufacturers don't want to spend money on power supply filter capacitors since batteries don't really care if they're pulsed during charging)
Using the voltage from a battery charger you can test a tach since depending on where the switch is set it'll read the 120 cycle per second as 120 pulses per second (which for a V-8 would be 1800 rpm)
Here's a description of how to do it.
http://www.route66hotrodhigh.com/TestingTach.html
I'm not home right now but when I get home, I am going to test an old marine tach I have using one of my el-cheepo battery chargers!
I think the output of the charger with no load might be somewhat high, so I might put an incandescent lightbulb or other resistor in series with the "plus" lead to limit current.
Do a little reading on the subject and you might find it's fairly simple to test a tach either by hooking it up to your car engine or using a battery charger.
Regards,
Rick