help! tach issues

DJ87

Seaman
Joined
Dec 20, 2010
Messages
65
Today is my first time using these forums and i must say being a first time boat owner i have learned alot. I was trying to figure out how to get my tach to work in the force engine forum and saw a posting saying that you might know what to do. what i have is a 20 foot 1987 bayliner with a force 125 outboard. The boat had been neglected and i had to rewire, carpet and upholster it. the dash had been altered and cut out to fit only a fish finder.i dont know what was there before but i removed all that and made a new dash plate with 4 gages, fuel, speed, tach and volts. My tach doesnt work right and reads much higher then it should. I went through the wire schematic and have it wired correctly into the strip on the side of the engine , on the terminal that says tach and has a purple wire going to my rectifier. I read somewhere tonight that it appears i have a 20 pole alternator and its very outdated. They then go on to say that todays systems are a 12 pole and thats why the new tach is all over that place. Is there something i can do to my current tach wiring to get it to work? If not do they even make a tach that works for my boat?:confused:
 

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: help! tach issues

Yes, you will need a special 20 pole tach. Nothing can be done to the ones made for a 12 pole stator.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: help! tach issues

What everyone says is true. But the reason this is true is because the tach works from pulses from the charging system. Your engine has a 20 pole stator that produces 10 pulses per revolution of the engine. Most current engines have 12 pole stators that produce 6 pulses per revolution. Other variations were 10 pole (5 pulses). Since your engine is applying 10 pulses to a tach designed to handle a maximum of 6 pulses you can see why it is reading much higher than it should. Your only solution (at least economically) is a tach that can handle 10 pulses. Great Lakes Skipper is the place to go for this.
 

DJ87

Seaman
Joined
Dec 20, 2010
Messages
65
Re: help! tach issues

thanks guys, i have ordered one, merry christmas!
 
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