New tachometer questions

[KG]

During my engine overhaul project, I'm planning on replacing my tachometer with a new one. My mechanic has suggested that a new Mitchell tach is not much more expensive than overhauling my old tach.

I see on a couple of on line sources that the Mitchell D1-112-5023 is the replacement for the Cessna 170. It is listed as having an average cruise rpm of 2300. Is this the correct tach? I normally cruise at a higher rpm than 2300. Does it matter? They list other tachs with different average cruise rpms.

Also, for an additional charge, they can put custom markings on the tach face. Did I read somewhere that this is a requirement? What markings would you experts recommend that I have put on the tach? Red line, obviously. Anything else?

My mechanic also told me that he has had poor results lately from replacement tach drive cables. He said out of the last five or six he installed, only one worked correctly. He said some have come kinked and bent and others, for reasons unknown, cause the tach to twitch. That's what my old one does so I don't want to replace it with a new twitching tach. Anybody else run into problems with new tach cables? Any suggestions to insure I get a good tach cable along with my new tach?

Thanks,
Keith

[GAHorn]

That is the correct tach, and if the cable comes kinked or bent...reject it back on the seller.

The tach markings (for the C-145) are described in AFM:
Red Line = 2700 (All Models)
Green Arc - 2200-2450 (A and B models)

[cessna170bdriver]

During my engine overhaul project, I'm planning on replacing my tachometer with a new one. My mechanic has suggested that a new Mitchell tach is not much more expensive than overhauling my old tach...
Thanks,
Keith

Keith, I had the same debate with myself during my overhaul 5 years ago. I ended up going with a new tach and I'm glad I did. The "twitchiness" in my needle must have been due to the internal condition of the (50+ years old) tach itself, as the new one is rock steady, even with the 15+ year-old (~1000 hours) tach cable. With the old tach, the "twitch" range was about 100 RPM, making the tach next to useless for purposes, say, of leaning for maximum power. Now, the slightest change in RPM is evident.

...It is listed as having an average cruise rpm of 2300. Is this the correct tach? I normally cruise at a higher rpm than 2300. Does it matter?...

I wondered about the 2300 RPM tach myslef, given that nominal cruise is about 2450. I log clock time from master switch on to master switch off, and as it turns out, tach hours with the 2300 RPM version run pretty close to clock time for a given flight.

...Also, for an additional charge, they can put custom markings on the tach face. Did I read somewhere that this is a requirement? What markings would you experts recommend that I have put on the tach? Red line, obviously. Anything else?

When I get home, I'll find and post a photo of how I had mine done. If I remember correctly, George blessed it, so it MUST be right!

[bagarre]

++ interest in those markings.
I'm replacing my tach this year too. Current one has no markings and has the +- 100RPM bounce.
What's the right cable/length for a '52 170B with an 0300D?

-David

[GAHorn]

....What's the right cable/length for a '52 170B with an 0300D?

-David

It depends.

Where is your tach mounted versus the rest of the fleet? (see the problem?)

Suggest you remove yours and if you like its length...measure it.

[bagarre]

Good point. Mine is in the far right side of the panel.
I was hoping to pre-order everything without taking the plane apart to keep down time to a minimum.

[cessna170bdriver]

Here's a photo of my tach with custom markings as received from Aircraft Spruce. According to my records, it is a Mitchell D1-112-5024. I seem to remember it took a week or two to be delivered, and was $203 in 2006. I also seem to remember they would preset the hours to any value you requested. I chose to leave it at zero so I could keep track of TSMOH without doing any math.

TachAndCalibration.jpg

I wondered about the 2300 RPM tach myslef, given that nominal cruise is about 2450. I log clock time from master switch on to master switch off, and as it turns out, tach hours with the 2300 RPM version run pretty close to clock time for a given flight.

Checking the part number I ordered, it is geared for hours at 2400 RPM.

[rhymes]

I too replaced our tachometer with the Mitchell, and had them put the RPM ranges on, as well as reset the hour meter to TTAF.
It took three tachs and cables, sent back and forth, before the tach would stop bouncing and give an accurate reading... but the Mitchell folks were very helpful, and just as perplexed as I was. After a couple hundred hours, it's doing great now. Reasonable price too, as I recall.
I'd buy from them again, and hope the gremlins stay away.

[KG]

It took three tachs and cables, sent back and forth, before the tach would stop bouncing and give an accurate reading...

That is what my mechanic is saying too. Coincidence? I'm wondering if there is a production / quality control issue somewhere. My mechanic thinks it is the cables giving the problem. I'll report back if I run into the same thing.

[KG]

Here's a photo of my tach with custom markings as received from Aircraft Spruce. According to my records, it is a Mitchell D1-112-5024. I seem to remember it took a week or two to be delivered, and was $203 in 2006. I also seem to remember they would preset the hours to any value you requested. I chose to leave it at zero so I could keep track of TSMOH without doing any math.

TachAndCalibration.jpg

Thanks everybody. I'll be ordering one marked like that today.

[GAHorn]

Look at my tachometer. It's was installed (reading zero hours) at completion of my airplane's restoration 13 years ago, it's horometer reading is same as engine time.

In this picture, (taken for the right-seater-course expertly delivered by Bob Lavery at the 2007 GLS convention), the engine is RUNNING at cruise RPM, and has over 721 hours and the tach has over 13 years on it.

MVC-002S.JPG

LOOK how steady that needle is! NO TWITCHINESS!

Get the Mitchell. Don't bend or kink the cable.

[KG]

That is one steady tachometer!

Here's an update.... I just talked to Spruce and ordered a tach. They said they had them on back order from Feb of 2010 until Nov, when they got in a shipment of, I think she said, 60. Those are all gone and they are again on back order.

As I waited, she called Mitchell and asked about shipping dates and she told me that if I ordered with custom markings, which I planned to do anyway, it would be shipped direct from Mitchell and I would get it quicker. They said to expect about two weeks. We'll see.

I'll keep you posted.
K

[Bruce Fenstermacher]

I don't know. If you click to enlarge the picture I think you'll detect a twitch.

MVC-002S.gif

[HA]

that ghostly image of a guy with a camera would distract me, can that be polished out?

[GAHorn]

I don't know. If you click to enlarge the picture I think you'll detect a twitch.

MVC-002S.gif

A-HA!

So it's BRUCE that causes all these problems!!!