So, why are tachs so unreliable....and what's the solution?

Yeah the switch panel is buckling in the direct sunlight. It goes away when it is cool. When I got the panel is was about 1/4" too long and I sized it to fit and did not leave enough clearance on each end and so when it gets hot it buckles. I just have not had the time (think days) to take it all back apart and sand both ends off 1/8" and open up the screw holes a bit. But I will.

Pete
 
Yeah I know. drives me crazy when it buckles. But it is SUCH a pain to take out all those switches. I may try to trim the ends without removing the switches. I used Flounder Pounder. I talked with Ken Gearin and he was great to work with. In hindsight, if I had time, I would have removed all the panels and shipped them to Flounder Pounder so that could have adjusted the cut files and made the parts so they were exact copies. All the parts I received were a little bit too long and I had to trim them. I just clamped the old one over the new one to the dock and used a drum sander bit in my cordless drill. So it wasn't too bad, just could have been easier. I also made a great mod and put dual dimmer switches. One for the instrument panel and the other for the backlighting of the switches. They never dimmed equally before and now I can dim them independently. I also bought the new dimmer modules from FP.

Pete
 
The pulses come from the teeth on the flywheel. There are 126 teeth on the flywheel and that many go by the magnetic pickup for each revolution of the engine. So set the tach dip switches to the proper settings for a 126 PPR.

Enjoy! I love mine and love watching the synchronizer keep the engines to +/- 1 rpm

Also fun the watch the admiral try and get them exactly the same with the levers.

Pete
 
Out of curiousity, how does the engine computer arrive at an RPM reading?
 
Ok. So how do your engine computer know, misterCOMPUTERman? ;-)
 
rondds said:
Ok. So how do your engine computer know, misterCOMPUTERman? ;-)
Click to expand...

Damn if I know. The ECM outputs to the tach. The ECM inputs from one of these places.

8.1.jpg
 
Yikes!
Sorry I asked. Maybe it counts teeth also.
 
You're a dentist. Every one of your answers is about teeth.

Although the crankshaft sensor (counting teeth) may actually be the source of tach signal on an ECM based engine.
 
Yes the 126 teeth on the flywheel are the gear teeth for the starter motor, and that is bolted directly to the crankshaft. The Cat 3116 and 3126 have no electronics on helping them run. They are purely mechanical. The sensors for the gauges are electronic, but there is not computer or feedback from those sensors back to the engine. Very simple and yes only the wire to the fuel solenoid is required to run the engine.

More analog tachometers are really only voltmeters. They take pulses from a source like the magnetic pickup or from an alternator or the coil on a gas engine and use capacitors and resistors and maybe diodes to turn the pulse train into a voltage level that is displayed by the tach. The Digital Tachs are more sophisticated and use the pulse train and compare the pulse train to a timer in the electronics. By measuring the time between pulses or the number of pulses in an certain amount of time the electronics can make very accurate measurements of the RPM. The 3116 sends 126 pulses to the electronics every revolution. If you are running at 2400 rpm the electronics are getting 5040 pulses per second and so the electronics can easily resolve one rpm.

Pete
 
For those of you that saw the picture of my Dash that was buckling I just want to say some nice things here about Flounder Pounder and Ken Gearin. Apparently someone sent Ken the thread and the picture of my dash and he went out of the way to contact me through CSR to offer to replace the panel with one that is modeled off my old panel. I had previously sent him pictures of the dash and the resolution of the problem kind of fell through the cracks with the busy summer and the somewhat foreboding task of taking out all the switches again, but I am very impressed that Ken went out of his way to save me a matching piece of the dash material and offer to make me another dash panel. That is real customer service!

Thanks Ken,

Pete
 
I have Aetna Tachs on my flybridge and love them! The lower helm still has the old tachs and they are about 75 rpm off at cruise power. When I use the lower helm I set the power on the bridge and then go downstairs. I want to replace the lower ones soon as the Aetna Tachs are far superior.
 
Nice! Who made up the panel for you and how much did it cost? Did you send them templates for the new tachs and the gauges?
 
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