Help me replace my tach

SixPapaCharlie

SixPapaCharlie

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I took off and a few hundred feet up, I hear this God awful screeching noise and see my tach dancing wildly.
I land, go to my MX and we replace the cable with a brand new one. Screeching stopped but RPM seems to read higher than I am used to and still dancing just a little (50 ish RMP).

Yesterday, I see the tach dancing a little here and there and for fractions of a second, I hear that same "screeching" noise in the panel. Not consistent, just chirps.

Dumb question: Do all the digital tachs use a mechanical connection to the engine? I am guessing something is slipping and I am under the impression there is an alretnate wat yo get your RPM based on my mechanic's suggestion. He suggested I put a 5k engine monitor in. He said that will eliminate the mechanical connection.

I am not sinking that into my plane at this time but his comment seems to suggest to me that there is an alternate to the mechanical linkage.

What do I need to knnow?
 
Electronic tach with digital readout will be an electrical connection that reads mag pulses. No mechanical connection.
 
When I researched a couple years back, there was Horizon Instruments and Electronics International.

One was a nice larger size numerical readout, with an LED analog type display in addition, while the other had a cool mag check function. One started the tach hours clock at a lower RPM than the other. Unfortunately, neither one was “perfect”. I can’t remember which was which.

I ended up living with my mechanical until the day it gives out; I keep an optical tach in my glovebox and check the accuracy of the mechanical from time to time. It was a nice gift for Christmas or birthday, can’t remember.
 
455 Bravo Uniform said:
When I researched a couple years back, there was Horizon Instruments and Electronics International.

One was a nice larger size numerical readout, with an LED analog type display in addition, while the other had a cool mag check function. One started the tach hours clock at a lower RPM than the other. Unfortunately, neither one was “perfect”. I can’t remember which was which.

I ended up living with my mechanical until the day it gives out; I keep an optical tach in my glovebox and check the accuracy of the mechanical from time to time. It was a nice gift for Christmas or birthday, can’t remember.
Click to expand...

We have the Horizion, and it works well, but I don't see it for sale at the moment.
 
Are you sure the screeching isn't coming from the engine and the rpms are actually bouncing around? j/k :D
 
I wonder if Horizon is having pandemic related business problems?
 
I still have the mechanical tach and will replace it next as it no longer tracks air frame time. I plan to replace it with an Electronics International CGR-30 for a number of reasons.
It does away with the mechanical linkage to the engine.
It adds engine monitoring
It gives me fuel flow
It replaces a lot of old temp/pressure gauges
It adds additional information gauges such as those to each cylinder and in turn-
It records information for troubleshooting problems I may have
 
455 Bravo Uniform said:
Electronic tach with digital readout will be an electrical connection that reads mag pulses. No mechanical connection.
Click to expand...
I have a jpm 930 in my new plane, and the original tach is still in the dash as well. The jpm reads about 100rpm lower than the mechanical. I tend to trust the jpm more, but but I haven't verified it. The jpm is certified as primary and takes its reading from a sensor glued to the magneto.

I once had a motorcycle tach that was sluggish and obviously read low. Opened it up and wiped some schmoo out from between the spinny bit and the needle, and lo and behold it worked perfectly. (Or as near as I could tell) Since then I've taken mechanical tach readings with a grain of salt.

I know there's people who rebuild old car and motorcycle tachs; i assume the same service is available at inflated aviation prices.
 
I replaced the mechanical tach with a new mechanical tach in my last plane and I remember it costing like $100. If your not gonna go all the way to
Engine monitor just fox what you have.


Sent from my iPhone using Tapatalk
 
455 Bravo Uniform said:
That’s pretty much it for “certified” installations, in a digital format. Next up are the engine monitors.
Click to expand...
What about this one? Looks like @SixPapaCharlie 's AA5 is on the STC AML.
http://www.aerospacelogic.com/index.php?dispatch=products.view&product_id=53
53_TM200-1.jpg
 
I sent a Stewart Warner mechanical tachometer P/N 551-TA to Century Instruments after experiencing a crazy loud squeal and the needle falling off. Its was $145 + shipping. I think it took about 10 days. Yeah a new tach cable was another $60 from Textron.

333 hours later its still working fine.
 
Ok I have some questions. I am buying this one (Thank You @Bill ):
https://www.aircraftspruce.com/pages/in/tachometers_0browse/ei-digitalgraphic1.php

They want to know "Red Marking" "Green Marking" "Yellow Marking" on my current unit.
I have no yellow and Green is only from 2100 - 2700 so what color would everything below green be then?

Also what do the SL, 5 10 mean on my tach. Always wondered. Can't find the answer on google.

20201220_191711_resized.jpg
 
455 Bravo Uniform said:
When I researched a couple years back, there was Horizon Instruments and Electronics International.

One was a nice larger size numerical readout, with an LED analog type display in addition, while the other had a cool mag check function. One started the tach hours clock at a lower RPM than the other. Unfortunately, neither one was “perfect”. I can’t remember which was which.

I ended up living with my mechanical until the day it gives out; I keep an optical tach in my glovebox and check the accuracy of the mechanical from time to time. It was a nice gift for Christmas or birthday, can’t remember.
Click to expand...

\How does the optical work?
 
SixPapaCharlie said:
Ok I have some questions. I am buying this one (Thank You @Bill ):
https://www.aircraftspruce.com/pages/in/tachometers_0browse/ei-digitalgraphic1.php

They want to know "Red Marking" "Green Marking" "Yellow Marking" on my current unit.
I have no yellow and Green is only from 2100 - 2700 so what color would everything below green be then?

Also what do the SL, 5 10 mean on my tach. Always wondered. Can't find the answer on google.

View attachment 92616
Click to expand...

For your plane, no yellow. Everything below 2100 should just be blank. On the Mooney, we have a yellow warning band, "avoid continuous operation between 1500 and 1950 rpm below 15" manifold pressure." Example original tach below:

s-l640.jpg


Your plane appears to have no yellow band warning area, but be sure to consult your POH to be sure.
 
On our replacement Horizon tach, the yellow LED above the digital readout will be on when in the yellow band.

Capture.JPG
 
Suggest you have the Cable examined or replaced also.

Most Tachs have a “Boss” for a Lube Port.

Currently it appears the Boss is not machined to allow lubrication though.

A bad Tach can damage the Cable.

If you are replacing with a new analog type note that the recording portion

varies by Aircraft Type.

Typical Cruise RPM is factor.

Again note that that this feature DOES impact frequency of some maintenance

including AD compliance.
 
Magman said:
Suggest you have the Cable examined or replaced also.
Click to expand...
Been reading long? Your posts indicate an inability to use a thing called paragraphs, but that's okay.

Original post stated the cable was replaced:

SixPapaCharlie said:
I land, go to my MX and we replace the cable with a brand new one.
Click to expand...

BrYan... have it marked as the one removed. Hopefully you don't need to specify black background and white letters, numerals, and demarkations. :)
 
GeorgeC said:
Sea level, 5000, and 10000
Click to expand...

I didn't have those markings on my Traveler tach. Looking at the POH, I think the multiple green arcs at SL, 5000, and 10000 feet indicate rpms where it is safe to lean in cruise (below 75% power). I've got green and yellow arcs and a new redline now with the HC STC. For some reason that baffles me there is a yellow arc between 2600 and 2650 rpm, a limitation not explained in the STC, but required to be on the tach. I usually cruise between 2550-2600 rpm anyway, and it won't do more than 2500 rpm in a Vy or cruise climb with the Sensenich prop.
 
If anyone wants to stick with a mechanical tach, here is a vote for Mitchell. Can be ordered from Aircraft Spruce. Pull your old Stewart Warner and put the part number in the comments to help match. Also put the aircraft make/model, as Mitchell may have factory OEM faces. Here is the ACA face for my old Bellanca Super Decathlon, complete with required placards. Didn't realize how hinky my old tach was until I put the new one in. Rock solid steady and stable. Big increase in confidence for mag checks.
 

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Ed Haywood said:
If anyone wants to stick with a mechanical tach, here is a vote for Mitchell. Can be ordered from Aircraft Spruce. Pull your old Stewart Warner and put the part number in the comments to help match. Also put the aircraft make/model, as Mitchell may have factory OEM faces. Here is the ACA face for my old Bellanca Super Decathlon, complete with required placards. Didn't realize how hinky my old tach was until I put the new one in. Rock solid steady and stable. Big increase in confidence for mag checks.
Click to expand...

Was looking @ the Mitchell tachs. They are getting terrible recent reviews @ Spruce. Anyone having any luck with them? (other than Ed)
 
The squealing (and, often, the erratic indications otherwise) are from the tach's input shaft bearing. It's an oilite bearing, made from small bits of bronze pressed and fused together to form a porous bushing which is then immersed in a hot, thick oil that penetrates it and stays there to lubricate the bearing. But after 40 years that oil is gone or has sludged up due to moisture and dust and it starts getting sticky. The bushing also wears and clearance increases, and so the shaft, instead of rotating freely in the bearing, starts "walking" rapidly around inside it.

Magman mentioned the lubrication port on some tachs. That port is on the top of the bearing boss, near the cable nut, and a drop of light oil in it will often solve the problem for some time. That said, most old tachs are under-reading due to their magnet weakening with age and should be replaced anyway.
 
Lori L. Seymour said:
Was looking @ the Mitchell tachs. They are getting terrible recent reviews @ Spruce. Anyone having any luck with them? (other than Ed)
Click to expand...
Put one in out Scout about 2 years ago, no issues, I think it cost about $270.

BTW the "Engine RPM" App for the iphone works pretty good and reasonably accurate in quite a few planes to check the accuracy your tach. This was how I discovered/confirmed the old tach was reading about 200rpm low.

Brian
 
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