Tachometer sending unit not functioning RV-9A - O-320

[moll780]

During an oil change I noticed the tach sending unit located on the accessory housing on my O-320 was a little loose. I tightened it down. The tach was reading for another 2 flights and then stopped displaying on my Dynon EMS-D10.
I removed the tach (transducer?) from the back of the engine to see if the input shaft was sitting correctly and as far as i can tell it all connected the way it logically seemed it should. I spun the prop while putting my finger on the output from the engine and i could feel that it was turning. I hear what seems to be some rattling when i shake the transducer but since I've no experience with this type of device I am not sure if that is acceptable.

1. does anyone have any experience with this?
2. it seems like an easy enough part to replace. any thoughts of what its actually called and who might have this or a comparable replacement unit?

Thanks in advance for your help.

The unit highlighted in Yellow.
The nut that backed out is in Red.


The part number from the back of the device.


The wires going into the harness. All are solid connections.

[moll780]

Called Vans and they said I needed to go to Dynon for the Tach replacement.
Dynon said the tach is read from the P-lead.
So I bought a tiny-tach for a temporary fix but Im still looking for a replacement unit.
any info someone may have would be really helpful.
thanks

[rvbuilder2002]

I am making a couple of assumtions....


You did not build the airplane.
You did not receive any of the documentation for the installed equipent when you purchased the airplane.

It appears that someone mixed the use of parts that were not neccessarily needed.

The tach sending unit in your photo looks like what Vans sells, but if you gave them the number printed on the back, they would not recognize it (probably the manufacturers #).

Adding to the confusion is that I think your EMS-D10 should be able to sense the engine RPM off of the P-Leads, so your engine didn't need that tach sending unit installed (what Dynon tech. support told you).

I suggest you go to Dynons web site and get the documentation for the EMS-D10, and confirm whether you can sense off of the P-leads. If so, you then do not have to replace the tach sending unit.

[Andy Hill]

I suspect if you remove the back of the sender unit (which will essentially destroy it) you will discover a plastic rotor assembly (with a magnet?) in pieces.

Ask me how I know

I think it is this Vans part IE VTACHGEN 2

As you've been told, use the P-Lead (+ Resistor!) for the Dynon.

Andy Hill
RV-8 G-HILZ
RV8tors

[Low Pass]

Check the thrust clearance on the transducer drive shaft. You've overtightened the assembly, putting the shaft and rotor in a bind. Did it twice before figuring it out. Can't remember how I corrected the situation - spacer washer, trimmed the shaft?

[etekberg]

That looks like a vans tach sender to me. They seem to fail on me every couple hundred hours or so. I've replaced one or two in my time.

[moll780]

thanks for the info!

Correct, I'm not the builder and have no access to him, yet (he passed away).
Im just a flier and eagerly learning the mechanical side of the wonderful plane I am flying (best choice I could have made).

Yes, the D10 is P-Lead capable. I downloaded the installation PDF and as easy as it sounds to setup from single paragraph which basically says "wire into the P-Lead of the magneto with a 30k Ohm resistor", it leaves me a little wondering "what the heck"?.

I'm going to try to replace the original part and figure out the P-Lead somehow. 2 tracks will at least lead to one solution and get me back into the air.