Tach guage may be off

[1CoeRay77]

I thing my tach gauge may be off about 1000 rpm's. I used a laser rpm tester, the dash gauge was reading 4000 and the tester was reading 3000. This tester requires a metallic sticker to be placed on something like the balancer wheel, but im not sure if i had it on that or not.
Is there another way to test my tach, with a volt meter possibly? My digital hour meter does not work either, it is reading 24hrs and the boat has around 300hrs on it.

 

[RickJ6956]

Re: Tach guage may be off

Most marinas have a tach they use when they perform service.

 

[Silvertip]

Re: Tach guage may be off

You can't measure RPM with a voltmeter. The rpm you measure using an external tach like your laser or infra red, must be reading the "crankshaft" rpm, not any of the pulleys. The crankshaft is what drives the boat. Any of the accessory pulleys like the alternator and power steering pump are not driven at the same speed as the crankshaft so if you don't have the reflective/magnetic tab on the crankshaft pulley you are not getting an accurate reading. Your hour meter needs only 12 volts and ground when the key is on. That you can measure with a voltmeter.