Look at this video of my tachometer

[blackrider]

Hey guys,

Hoping someone here can give me a bit of insight to my tachometer acting up. Just bought the boat and the RPM gauge showed me idling at 2000 RPM. I would guess the engine was actually somewhere between 750 to 850 RPM though while the tach was showing me at 2K RPM. I read up on here about the switch in the back and I checked to make sure it was on 4 cylinder. So I pulled it off to clean the terminals just for the hell of it and this is what I found the needle doing. Is this normal?? Doesn't look like there is anyway to take it apart either. I have a spare SunPro tach that I can use for the time being. Will this work until I can buy a Teleflex one? Unfortunately I am tapped out on money due to the bellows, water pump and gimbal repair.




Thanks

 

[glenn property of pam]

Re: Look at this video of my tachometer

a tach is just a floating needle when theres no power attached to it so turning it upside down doesnt realy prove anything. A tach will also stay at the last setting when power is cut to it so dont expect it to go to zero until you turn the key back on. The number on the back depends on the motor and the set up. We would need to know what type of motor you are connecting the tack to. If you are connecting to a outboard then the tack is set to the number of magnets under the flywheel as thats whats causes the ac signal the tach reads ( i think mine is set to 12 )

 

[blackrider]

Re: Look at this video of my tachometer

a tach is just a floating needle when theres no power attached to it so turning it upside down doesnt realy prove anything. A tach will also stay at the last setting when power is cut to it so dont expect it to go to zero until you turn the key back on. The number on the back depends on the motor and the set up. We would need to know what type of motor you are connecting the tack to. If you are connecting to a outboard then the tack is set to the number of magnets under the flywheel as thats whats causes the ac signal the tach reads ( i think mine is set to 12 )

OK so this is normal! Well that's good. After posting this video I threw it back in the boat and used a small jewelers flat head screwdriver to turn the calibration button as it was running. I was able to bring the dial down to 700 RPM's while the engine was idling. I don't know for sure if that's what the exact RPM is but I know for sure its a lot better than 2000 RPM's. I will have to use a timing light at some point to sync the tach. I read on here once that the light stays on steady at a certain RPM. So rev the engine until you have a steady light and then set the tach to that RPM. I just hope the tach stays this way. I am betting if I go out on the water for a day and get all bounced around it will throw it out of wack. As for the switch for the number of cylinders, if you read my initial post I said it was indeed pointing to the correct number of cylinders. It is a 4 banger.

 

[jhebert]

Re: Look at this video of my tachometer

Usually a tachometer is made as a universal device that can be used with a variety of engines, and it will have a multi-position switch on its rear face. The switch is typically marked with a legend. The legend is usually numbered in a sequence like 2,3,4,5,6. Changing the switch position changes the calibration of the tachometer. On outboard engines the signal that is applied to the tachometer is usually derived from a half-wave rectifier tap into the alternator output. This produces a pulsing DC signal whose pulse frequency varies with engine speed, according to the arrangement of alternator poles and magnets. Usually the numbers in the legend reflect the number of pulses that will occur for one revolution of the crankshaft.

It is not likely that the legends of the switch reflect the number of cylinders of the engine with which it is to be used.

 

[blackrider]

Re: Look at this video of my tachometer

Just an update incase anyone comes across this thread in the future. The RPM gauge stayed normal the entire weekend. I am not sure if this was dumb luck or if turning the calibration knob to bring the needle down to the near correct range actually worked. All I know is before it was showing 2K at idle and at cruise it was pegged. I feel so much better about the operation of the RPM gauge now. Even though you drive the boat based on the feel of the engine it is still nice to see everything on the dash operational.

 

[NYBo]

Re: Look at this video of my tachometer

It's possible that moving the switch cleaned up the contacts. Glad it worked, whatever the reason.