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skyyking

Active Member
I am in the middle of overhauling my engine for the project. I'd like to do away with the (mechanical) tach drive all together. Has anyone out there fitted an electronic tach with a conventional pair of magnetos?
 
skyyking said:
I am in the middle of overhauling my engine for the project. I'd like to do away with the (mechanical) tach drive all together. Has anyone out there fitted an electronic tach with a conventional pair of magnetos?
Click to expand...

Yes - this is done frequently. Most of the engine monitors can sense the RPM by looking at the P-lead to a mag.
 
Yes, but..

You have to wire it to one or the other. Since I wanted to be able to do the mag drop test correctly, I installed a two-way selector for which mag the tach is reading. No big deal, but necessary if you want to read from both which is the logical equivalent of using a mechanical drive off the engine.
 
No Mechanical Tach

hevansrv7a said:
You have to wire it to one or the other. Since I wanted to be able to do the mag drop test correctly, I installed a two-way selector for which mag the tach is reading. No big deal, but necessary if you want to read from both which is the logical equivalent of using a mechanical drive off the engine.
Click to expand...

That's how my Grand Rapids EIS is set up and it has worked flawlessly for over 800 hours.
 
skyyking said:
I am in the middle of overhauling my engine for the project. I'd like to do away with the (mechanical) tach drive all together. .....?
Click to expand...

Raymond,

Were you flying with it or just decided to go electrical? I will be installing the cable soon ( I like mechanical stuff) and looking for comments.
 
Electronic Tach

The tach below is in my RV6 with an O-360 and I love it. Check out the web site. The microprocessor continuously computes RPM from timing signals from the magneto's "P-lead" or primary coil grounding leads. Continuous comparison of the left magneto's RPM and the right magneto's RPM will yield an error indication if a difference if found to be greater than 80 RPM. With a two switch set up it can read the mag drop directly in RPM's.

http://www.horizoninstruments.com/prod01.htm


p21000uv4.jpg
 
Installing Tach Shaft?

Ray, will you be installing a tach shaft in your accessory case or leaving it out? If using electronic tach, you would not need this shaft to determine engine RPM. I have heard from one amateur builder who believes that he blew his engine as a result of not installing this shaft; his theory is that the tach shaft blocks oil from slinging off something (camshaft gear?) and entering the breather. Over the span of a flight, enough engine oil exited the breather tube so that he had a low-oil condition resulting in engine seizure.

Last weekend, I asked this question of John Haas, Mattituck's chief inspector during their TMX Engine Assembly Workshop, and he indicated that they have built engines without the tach shaft installed on several occasions and have not seen any problems. He thought the problem must have been something else. He also noted that there is a shield mounted to the accessory case which would prevent oil from slinging out the breather.

I'm still debating what to do when I reassemble my engine. I like eliminating moving parts which have no function and seals which can leak which now serve no purpose.

Have you considered any of this?
 
Horizon Tach

I second the recomendation of the electronic "Horizon" tach. I replaced a mechanical tach with one and could not be happier. The installation was painless and it has some great features. Check it out.
 
DO NOT LEAVE OUT THE TACH DRIVE!

A friend left out the tach drive and it cost him the engine.

As it turns out, there is an internal oil jet that is designed to spray oil on the tach drive. Without the drive in place the oil just goes out the breather hole.

Put the drive in the engine but cap it, if you are not going to use it.

BTW, E/P-mags provide a signal for an electronic tach.

PS. I left the tach drive out of my O-290 but the breather hole for my engine is on the front of the case, so this works for me.
 
I have a Superior IO360 with two mags and a Dynon EMS-120. There are two leads from the 120, one for each tach that attaches to the P-lead. Works fine.

greg
 
I too just put in a Horizon P-1000 digital tach... Haven't flown yet with it since replacing my flakey mechanical tach... Have little more work to do under the cowl... should fly tomorrow and actually see it work for me in the air... If your replacing a 3 1/8" gauge, this fits right in... Has some neat features...
 
Inductive Sensor

Both of my airplanes have an inductive sensor that is mounted in the vent of either tach to pick up rpms. One is EI, the other JPI.
 
MGL tach?

Anybody using a MGL tach that's sold by Chief? Looks like it will do everything I want a tach to do at an affordable price.
 
"A friend left out the tach drive and it cost him the engine.

As it turns out, there is an internal oil jet that is designed to spray oil on the tach drive. Without the drive in place the oil just goes out the breather hole.

Put the drive in the engine but cap it, if you are not going to use it."

Do you mean an internal drive part? or a part of the tach cable, cut short and then place a cap over it??? What do you mean "drive"...
I just removed the tach cable and put a cap on... Pulled nothing out of the tach attach spot other than the cable..
 
R-1 from EI all the way!!


210 Degree Arc: The R-1 displays RPM in a 210 Degree graphical LED arc for immediate reference. Red and Yellow LED's highlight cautionary and restricted operating ranges.

Tach Time: The R-1 keeps track of Tach Time on your engine, to .1 hours.

Flight Timer: Flight Time is recorded from takeoff to landing.

Peak RPM: For every flight, Peak RPM is stored. Simply press the "Pk" button to see the previous flight's Peak RPM.

Mag Drop: The drop in RPM when switching from "Both" mags to "Left" or "Right" on your ignition switch is displayed on the large, crisp LCD of the R-1. For instance, if the drop is 110, the R-1 will display "-110."

Mag Failure Alert: If a mag fails during your flight, the R-1 will alert you by intermittently cycling through the LED's several times as you make your approach to land. Several pilots have mentioned to our support staff that this "cycling" has caught a failed mag while in flight.


Special prices for vansairforce.com members!


reflect_R-1.jpg
 
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Sheldon said:
"A friend left out the tach drive and it cost him the engine.

As it turns out, there is an internal oil jet that is designed to spray oil on the tach drive. Without the drive in place the oil just goes out the breather hole.

Put the drive in the engine but cap it, if you are not going to use it."

Do you mean an internal drive part? or a part of the tach cable, cut short and then place a cap over it??? What do you mean "drive"...
I just removed the tach cable and put a cap on... Pulled nothing out of the tach attach spot other than the cable..
Click to expand...

The tach drive is a shaft internal to the accessory case about 4 or 5 inches long which interfaces to a gear to spin the mechanical tach cable. You cannot remove it without taking the accessory case off the engine. Your method is fine.
 
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