Verifying tachometer works properly

W

WALSHIE

Well-known member
Member
Joined
Jan 1, 2000
RO Number
2124
Messages
2,374
Something is up with my tachs.
I *think* the port is accurate and the starboard which is showing slower RPMS is not.

I have a synch guage so I set the port tack to 3800rpms then synch using the synch guage. The boat sounds and runs good. But the starboard guage is 3-400rpms slower.
Also the starboard guage sometimes goes whacky, the needle jumps to 500rpms and beyond...something I'd hear if was really happening so it isn't

There must be a way to verify how they are working.

I was thinking volt meter to both at the same time to verify readings.

Otherwise, is there an external tool?

What say you boatered?
 
Get a shop timing light. It has a tach in it. You can get them for about $29. Really good deal.
 
Or you could put a piece of reflective tape on the flywheel and shine an old-style straight tube type 60cycle/sec AC fluorescent bulb at it at night . The tape should stay still at exactly (900?) 1800 and 3600 rpm when you can compare to your tachs.

I'd suggest as the tach mfgrs. do,( after confirming wire connections at "tite&brite") to note the setting of the small rotary pulse setting switch on the back , rotate it back and forth to help clean contact corrosion then set back to original setting if that is correct for your engine and tach. Many tachs also have an rpm calibration screw once you confirm what actual rpms are.

The digital tach/timing light Charlie mentions can be really handy.
Inductive Tiny-Tachs are another of many reality check options too.

FWIW- I switched to digital dashboard tachs at both stations long ago (FloScan 9000's at lower and Aetna Engineering LCD's up top) and greatly prefer them . The F/S accurately read within 10rpm increments and the Aetna's are accurate to +/- 1 rpm I believe.
 
Good mention too Smitty. I have a photo tach like that from about 10 yrs back too, but have yet to use it since I have so many other inductive tach devices.

Yours is especially good for checking diesels, where the inductive ones don't work.
 
Thanks guys! I really think it's the gauge on the dash. The sending wire for the tach is on the coil and I just replaced the coil (unrelated) and no change. I will verify the readings and most likely replace or clean the gauge.

Smitty - thanks, that's perfect, it's on order.
 
If they are Faria then they could be sticking.
My Faria's alway stuck and a little tap may the needled jump.
They do have a lifetime warranty.
 
If you don't want to open the engine compartment and you don't mind multiplying by the number of cylinders you can buy a $3 iPhone audio spectrum analyzer app and look at the audio frequency of the exhaust or even the engine itself. Most noise is a multiple of the rpm.
 
Charlie. shouldn't it stay steady at any multiple of 120?
 
These are Faria gauges! I tried the tap method and it sometimes works.
Thanks for the info on lifetime warranty...once I narrow it down to the gauge, I will deal with removal and replacement in the fall.
 
You must log in or register to reply here.
Back
Top