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

Boat Guy,

The senders are on the front end of the engine (aft in a V Drive DA). I believe they are magnetic. The PO of my boat (OSD9 - RIP Dom) had a thread about replacing the analog tachs with Aetna digital tachs with great results. You might search for his thread.

Here is Aetna's website:
http://www.aetnaengineering.com/8905-LCD-tachometer.asp
 
Thanks, I've been looking at that as an option. My thinking was if the senders are magnetic then they are very accurate, no? Then it's just the analog gauges that are the issue. The thing is, without doing a dash replacement, I think the digital gauges won't look right. The originals are 5" and the Aetnas are 3" or something....

What I did see is a device that takes an analog signal from diff. gauges (like the tach) and converts them to digital signals for plotters.

http://www.digitalmarinegauges.com/...ge=vmj_softy.tpl&product_id=80&category_id=17

Since I just got the Raymarine C140w and it has gauges as one of the screen options, I was thinking of going this route and leaving the dash alone.

So it's the analog gauges that are the issue then? Makes sense, since when I bang on them they seem to settle down with better accuracy. I'm just not sure what's going on in there. Is there a way to make them more accurate? I wish there was a nice 5" digital solution.
 
Read down about 25 threads. Tach/speed problems. the selector switch is what you should try to excercize. Did you see a selector switch?
 
Regarding the senders. They are proximity sensors that sense the teeth on the flywheel ring gear. On the port engine you can see it threaded into the bellhousing next to the lower step down to the engine room. There is a critical measurement for the gap between the flywheel teeth and the sensor; if you unthread it make sure you get a measurement so it can be reinstalled with the correct gap.
 
Don't screw with the magnetic senders.....that isn't your problem.

You have the typical Teleflex tach failure syndrome. The ones with an LCD window and digital hour meters are a little better than the alalog hour meter tachs (both were OEM at different times), but neither one will last much over 3-4 years. The diesel tachs receive a signal from the number of teeth passing the tooth counter (i.e. the sender) and do not rely on ignition pulses for their signal so there is no selector switch on the back of a diesel tach.

I have 2 sets of Teleflex tachs I've removed and have had Aetna digitals for about 6 years now and love them. My approach was a little different than the stainless filler bezel in the thread referenced by Carter above. I timed the tach replacement to coincide with replacing the gauge & switch panels and just had the new panels cut to fit the smaller Aetnas:

new panel2.jpg
 
Don't screw with the magnetic senders.....that isn't your problem.

You have the typical Teleflex tach failure syndrome. The ones with an LCD window and digital hour meters are a little better than the alalog hour meter tachs (both were OEM at different times), but neither one will last much over 3-4 years. The diesel tachs receive a signal from the number of teeth passing the tooth counter (i.e. the sender) and do not rely on ignition pulses for their signal so there is no selector switch on the back of a diesel tach.

I have 2 sets of Teleflex tachs I've removed and have had Aetna digitals for about 6 years now and love them. My approach was a little different than the stainless filler bezel in the thread referenced by Carter above. I timed the tach replacement to coincide with replacing the gauge & switch panels and just had the new panels cut to fit the smaller Aetnas:

View attachment 32336

Frank, I believe I see a spot of dirt or dust in this picture. Has your boat cleaner been on vacation? Oh wait, that was on my iPad screen! Beautiful as expected. And to think the Admiral busts my chops for constantly wiping on the helm as I am running the boat.
 
Frank, I believe I see a spot of dirt or dust in this picture. Has your boat cleaner been on vacation? Oh wait, that was on my iPad screen! Beautiful as expected. And to think the Admiral busts my chops for constantly wiping on the helm as I am running the boat.

Now that's good Ken!
 
Frank, I've been considering the dash replacement route.... Though if you saw the laundry list of what I've already done / and is on going, you would understand my reluctance to jump into that. I'm also not sure what I want to do in the Nav portion. I just got a C140W plotter to tie into my existing stuff. I'm pretty happy with it so far. In fact, I might just use a NEMA converter to get the tach reading into the plotter while I decide what to do in the dash.
 
I agree with frank completely. Forget about the senders, they are not the problem. The tachs are crap. I upgraded to the Aetna Digital and they are amazing. My idle speeds were way low and I thought my sync was junk. The Digital tachs are amazing and allow me to set the idle correctly, note that the sync is spot on, and assure that I can operate at the proper WOT even when loaded. They are the only way to go. The only con with the tachs is not being able to dim them, but at least they are red and so don't spoil your night vision. The upgraded dash is amazing too and I used led light strips behind the dash which was a great upgrade from the electroluminescent backlighting.

dash.jpg

You will love the upgrade to Aetna Digital.

Good Luck,

Pete
 
Thanks for the info Pete....

Are you guys trying to get me to upgrade the dash now? Haha.

Pete, not to be critical, but do I see bucklingin your dash panel? The tachs do look nice.

So you are saying I can just keep the senders and replace the tachs with the digital ones and they are good to go?
 
Curious about the unanswered question from above. Do "diesel tachs" have a cylinder # switch on the back? Mine port tach was jumping around and not settling up on the right RPM. I dribbled in some contact cleaner and move the switch around and the problem went away (for now).

Here's a pic of something similar. The black rotary switch on the right side will allow you to switch from 4 to 6 to 8 cylinders on gas models...

FPMARINE
 
Ron,


Re-read post #13...I think I answered the switch question.

Pete's boat is a '99; Frank's is a '96. In 1996, Sea Ray mounter the dash panels on a rubber step bushing where the screw holes are drilled oversized to slightly under the size of the screw head. The rubber busing fills the void between the threaded part of the screw and the OD of the hole. That means when I tighten the screws on my panel, the screws swell the bushing when they get snug but never bind on the dash panel, and that allows the panel to expand and contract with heat/cold and the bushings give enough to keep the panels flat. If the panels are screwed directly to the fiberglass, you can get some expansion between t he screw holes that causes what looks like buckling.
 

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