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Tachometer Fluctuations shake

M

mantry

Well Known Member
(GRANTED GOING FROM MEMORY)
On my RV7 with O360 (No vacuum pump) I have what I believe to be the Standard VANS tach setup, which consists of a small 12" tach cable from the rear of the engine to a transducer and then electrically connected from the transducer to the electric tachometer (display) on the panel.

I've notice in certain cases the tachometer bounces around +/- 200-300 rpm.

I'd like to know if anyone has any suggestions before I go tearing into.
Should I remove the tach cable from both the accessory case and the transducer and clean and lube and put it back? Is it the transducer going bad? Could it be electrical connections somewhere between the transducer and the tachometer?

I've looked at the existing topics.

Thanks in advance!
Mark
 
Cable

I would start with the cable. Pull it out, and inspect for wear. If it looks good, lube it with a good speedometer cable lubricant from your local NAPA store. Reinstall and see if it is any better.
 
search the form archives...

On some engines, because of cable length (rotating portion), the square end only engages in the tach generator a very small amount. Over time, this can wear and it begins to slip until it fails to turn at all.
 
Sounds like a perfect plan guys. Will do! Yes I did see the part about it NOT engaging all the way, will take a look at that as well when I pull the cowl off. I'll post my results when I get around to do it. Glad I can do it will only the top cowl off.

Mark
 
Also check to see if the connecting internal cable is not too long. Initially I installed this sensor directly on the engine with the short stubby connecting pin. All seemed fine but after a couple of flights the rpm reading became erratic. On inspection I found the connecting pin ad punched the back cover off the transducer.
Since I had an EIS4000 I switched to the p-lead sense and omitted the tach sender.
I think the problem was the admission of light to the optical sensor caused the sending errors. I was able to reassemble the sensor and bench tests confirmed it did seem to be working.
 
Flight data systems T-30

And kiss the cable, transducer etc. goodbye. I went through the same problem with the stock setup. Could never get it to settle down. For less than $200 the T-30 has been way better. BTW I have replacement gauge etc. if you're interested.
 
In looking at adding the T 30 Digital tach. I have to connect the two mag wires from the tach to my MAG SWITCHES. Today I was looking at my mag switches they are two separate toggle switches with FASTON connectors.

Any suggestions/recomendations on how to get the two additional wires from the tach to the mag p-leads on the toggle switches?
Here is a pic of the backside of my two mag switches:
2dalj6v.jpg


Determine which is GROUND and which is the p-lead and then cut off the FASTON connector and strip the wire and then include the tach wire with the p-lead and crimp them both into a new FASTON and plug it back on the switch?

Thanks folks!
Mark
 
One way would be to use something like THIS

You can also google double spade connector or dual spade connector to find many options.
 
Stopped by a friend who works in a TERMINAL shop and picked up a handful of those Double Spade terminals, looks like they will work great. I was a little concerned about quality control and if they would fit tight and not wiggle off and they look like they will be great!
 
Going to be working on installing the T 30 Electronic tach this week. They mention that you need to install a supplied resistor on the two leads that go to the mag switches. I will be using a FASTON crimp connector on those leads but I'm wondering how I should incorporate the resistors on the leads?

Suggestions?

1. Take the FASTON and cut the lead of the resistor and crimp one end of it in the FASTON and then crip the other lead of the resistor to the wire leading to the tach via a crimp on butt connector?

2. Same as above but solder the resistor lead into the FASTON and then solder the tach lead on to the other end of the resistor and cover all in heat shrink?

3. Crimp a short 2" piece or 22 ga wire into the FASTON and the solder the resistor to it and the lead going to the tach and cover in heat shrink?

or
____________

Thanks in advance and always appreciate the help of all the folks here.
 
Tach resistor

3- short wire soldered to resister, than other resister end soldered on to tach lead. Solder in a 'Z' (like Zoro) configuration, than heat shrink over. Distance between -lead & resistor should be minimized.
 
Thanks Ralph!

By "Z" I assume you mean cut the leads of the resistor to say 1/4" and bend the 3 legs, lead - resistor - lead in a "Z" configuration with the resistor being in the middle of the "Z". This as opposed to 2" of wire, soldered onto 2" of resistor lead, resistor, 2" of resistor lead, wire to tach.

I was was going to trim the leads back but didn't think about the "Z" configuration. GREAT IDEA! That keeps it all a small neat little package and again keeps it short and compact. THANK YOU!
 
mantry said:
Thanks Ralph!

By "Z" I assume you mean cut the leads of the resistor to say 1/4" and bend the 3 legs, lead - resistor - lead in a "Z" configuration with the resistor being in the middle of the "Z". This as opposed to 2" of wire, soldered onto 2" of resistor lead, resistor, 2" of resistor lead, wire to tach.

I was was going to trim the leads back but didn't think about the "Z" configuration. GREAT IDEA! That keeps it all a small neat little package and again keeps it short and compact. THANK YOU!
Click to expand...

There's a good EAA Hints for Homebuilders video on this...

http://eaavideo.org/video.aspx?v=713336874001
 
Last edited:
Perfect Ralph, I was making up the TACH cables yesterday and I was bending the leads of the resistor to form a "Z" and then soldering the wires onto that. Now from the video "Picture tells 1000 words" that I see that it is really more of a CRISS-CROSS

wwwwwwwwwwwwwwwwwwww+
|----RRRRRR----|
+wwwwwwwwwwwwwwwwwwwww

Or I might as well just attach the picture:
2hqatsk.jpg


I'll redo them today. Tried to go by Radio Shack for some more 20K resistors but they didn't have any. I bent one of the resistors and cut the leads too short . So I'll go to the other electronics store. I'm going to pick up the other suggested values just in case.

Mark
 
2qlh6b8.jpg


OK, after a long extended absence I finally got the tach installed and then got a chance to fly with it.

Let's just say it works great!!! Plus, I've been known to fly a short flight with just one of the mag switches turned on, proof that I didn't follow a checklist and probably didn't do a proper runup! Now with the T-30 tach that should be impossible as if it sees 1 tach 300rpm less than the other then it starts to flash at you!

I'm happy removing the VANS system and installing the electronic! Recommend!
 
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