How do you check tachometer accuracy?

[skyking897]

Well the title about says it all. If my tach is correct, I'm way underpropped. Let me back up and start over. I bought this boat last fall and everything was ok on the test drive and still is except the tach ( I think). At WOT the tach is reading 5500RPM today but the engine didn't sound like it was screaming. Performance is as I remembered it... except the 5500RPM. How do I go about checking its accuracy?

1986 Sylvan Offshore 22
140 Mercruiser/Alpha
Michigan Prop 14 3/4" X 15P

 

[sschefer]

Re: How do you check tachometer accuracy?

Borrow a timing light with a built in tach. They're usually pretty accurate.

 

[mcastles]

Re: How do you check tachometer accuracy?

Laser tach. I found my boat tach was 300 rpm off when trying to re-prop. GPS speed and accurate rpm's at WOT are critical for proper prop selection

 

[Chris1956]

Re: How do you check tachometer accuracy?

I would think your tach is way off. If that 4 banger was running at 5500 RPM, you would know it, and likely see pieces flying about.

I would think most any dwell tach would work on that motor. It is likely to be 1500 RPM off or so....

 

[skyking897]

Re: How do you check tachometer accuracy?

Thanks for the info, I'll look into a dwell tach meter and check it against the in dash tach.

 

[Mischief Managed]

Re: How do you check tachometer accuracy?

Smack the tach. while it's reading high. Faria tachs are notorious for reading high now and then.