No primary Tach

Challenged

Challenged

Pattern Altitude
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Apr 4, 2011
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Challenged
My primary RPM gauge is dead, but the one on my JPI is fine. What's the likely culprit? And I'm just curious if you'd personally fly a plane in this condition.
 
Meh.....if a band of Indians were after me I'd run it, but, otherwise not.

Plus, the tach is required equipment.

the culprit?.....broken cable or bad instrument.:yes:
 
Challenged said:
My primary RPM gauge is dead, but the one on my JPI is fine. What's the likely culprit? And I'm just curious if you'd personally fly a plane in this condition.
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Unless the JPI is a certified primary replacement you're not airworthy.
 
Challenged said:
My primary RPM gauge is dead, but the one on my JPI is fine. What's the likely culprit? And I'm just curious if you'd personally fly a plane in this condition.
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If it's a cable drive tach, I'd look at the cable first, and when you pop it out the back of the head, stick a little screwdriver in the drive socket and give it a spin. Mechanical tachs are dirt simple, if the needle doesn't bounce when you give it a flick/spin, a magnet fell off.

If it's electric, the common problem is a bad wire-pin connection at the cannon plug on the tach generator, or the generator itself.
 
Henning said:
Underpaid, but fun for a while. I don't mind turning wrenches, and diagnostics are fun, but it's not what I want to do for a living, you have to work and bleed too much.
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but....I don't bleed. :lol::rofl::D
 
This sort of problem usually pops up just before you land at wherever your A&P works.
 
It's a cable drive tach, and the JPI is not certified ( but seems to be more accurate and reliable, heh )
 
Challenged said:
It's a cable drive tach, and the JPI is not certified ( but seems to be more accurate and reliable, heh )
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Check the drive core on the cable, they typically pull out from the head side. Before you pull the core, check to see if you can turn it. If you can, and the cable comes out solid, you have a problem at the drive. If not, and the cable comes out good, you have a problem in the head.
 
Challenged said:
Thank you. And all this time I thought you were an A&P.
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Nope, just spent 4 years doing the work, and 40 years working on most anything that moves. All this stuff is the same, physics doesn't change by application, and seriously, the tach in your plane is identical to the one on boats and tractors around the globe, and mechanical speedometers are identical. This is 150 year old technology.:lol:
 
I doubt his has a magnet....or a tach generator.....more like slip disc/rings.
 
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As for not flying it without a tach, you drive most cars without one don't you? (Not to mention you actually have one more accurate anyway) Is it required by the FARs? Yes, but if the problem isn't causing oil to pour out of the engine, airspeed reference combined with sound should suffice you a safe flight over to get it fixed if you need.
 
Henning said:
Then either you're dead, or way more careful than I can bother being.:lol: Damn, working on airplanes always had me bleeding. No shortage of sharp sheet metal in tight, blind, places.:nonod:
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You forgot the boneheads who are too cheap to buy a pair of flush-cutters and leave Tywrap ends as sharp as razor blades. :mad2:
 
Norman said:
You forgot the boneheads who are too cheap to buy a pair of flush-cutters and leave Tywrap ends as sharp as razor blades. :mad2:
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Ugg, the bane of the late 20th century. The Snap On man gave me a neat little premium tool with a set of wrenches I bought; it's a T handle tie wrap tool. You slip it over the tail against the latch block then pull the T handle with your finger toward the palm stop to tighten it by making a fist, then you turn it 90° and it trims the tail off nice and tight. Makes doing the ones in tight places a breeze.
 
Henning said:
If it's a cable drive tach, I'd look at the cable first, and when you pop it out the back of the head, stick a little screwdriver in the drive socket and give it a spin. Mechanical tachs are dirt simple, if the needle doesn't bounce when you give it a flick/spin, a magnet fell off.
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If you spin it backwards will it take hours off of the engine time? :D
 
What's the hassle involved in getting the JPI certified? I'd remove the tach if it were my airplane.
 
I had a tach go bad once. It happened on runup and the needle just kept going around past the end. When it happens like that, its the tach, not the cable. When the cable breaks it just goes to zero.

When I sent it in to be rebuilt the guy asked me how many hours I wanted the tach hour meter to read..... (buyer beware)
 
Challenged said:
I'd have to replace it with a 900 series JPI instead of the 800 series I own.
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I really think the full glass 'primary' engine panels available are one of the best values for what you get, plus it frees up a lot of panel real estate that allows room for for doing a dual sided panel, one with a IFR legal six pack, one with an EXP SVT PFD.
 
I agree, in terms of what I got, the price isn't all that bad. Maybe if I tell my avionics shop that I want to trade up to 900 I can convince them to put that Grand Rapids EFIS system in ;)
 
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