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Tach is off, who can recalibrate?

R

RookieCubPilot

FRIEND
I recently bought a super cub and the tach reads higher than what the motor is truly running. Tonight we placed a tach that counts prop blades on the dash and compared it to the one in the plane and had a difference of 350rpm. Installed tach read 2700 and the portable tach read 2300-2350

Who do you know that could recalibrate accurately it and get it back to us quickly?

Is recalibrating the best route?

Appreciate the help!


Sent from my iPhone using SuperCub.Org mobile app
 
You can have it overhauled, takes some time, and by the way, they only have to indicate within 100 rpm to be legal. I had a similar issue, bought a new mechanical tach and it read 100 high. Sent it back and bought a Horizon electronic tach.....dead on every day.....I’d never screw with a mechanical tach that’s off again. Go electronic. Knowing what your engine is actually doing is important.

MTV
 
RookieCubPilot said:
When you buy a new tach can you transfer the hours over or do you have to start at 0 hours and note it in the log book?
Click to expand...
When I installed a new Horizon electronic tach in my 185, Horizon set the hours to what I told them. So yes, you can transfer the hours.
 
I've bought Mitchell mechanical tachs from Aircraft Spruce and get them in a few days with the hours set.
 
Too bad you are not experimental. These are usually simple automotive speedometers, and auto speedometer shops are really good at fixing and calibrating them. Mine all have airframe time set in the odometer, and I get a certificate of accuracy. Makes logbook entries lots easier.
 
The most accurate are the electronic tachs. As said above, check out Horizons and Electronics International units. If you go that route let them know what hours you want set on them whenyou place the order.

If you insist on the mechanical tach, talk to the automotive guys that repair/restore old car gauges. That's what these are to begin with. Have your A&P note in the log books that the tach was removed for repair, re installed, and checked for accuracy with the hand held tach.

Web
 
wireweinie said:
If you insist on the mechanical tach, talk to the automotive guys that repair/restore old car gauges. That's what these are to begin with. Have your A&P note in the log books that the tach was removed for repair, re installed, and checked for accuracy with the hand held tach.

Web
Click to expand...

Web that’s not even remotely legal. I wouldn’t sign it off.
https://www.ecfr.gov/cgi-bin/text-i...a4cfb2cd2&mc=true&node=se14.2.65_181&rgn=div8

I agree with going to an electronic tach. I like Horizon and EI’s products.

Charlie
 
Last edited:
It's getting to be an orphaned part, as in no aircraft shops are willing to work on them. A broken tach is not going to make an aircraft crash before you bring it home. If it makes everyone feel better, remove a broken tach and install a 'serviceable' one.

Web
 
I am with Web. Of course you never sign off a tach that has been worked on by an automotive expert. That is now against the law.

Don't forget to put a touch of black paint on those 6-32 instrument screws. Don't want shiny brass staring at you.
 
bob turner said:
I am with Web. Of course you never sign off a tach that has been worked on by an automotive expert. That is now against the law.

Don't forget to put a touch of black paint on those 6-32 instrument screws. Don't want shiny brass staring at you.
Click to expand...

Well we can agree to disagree. Kind of reminds me of the inverted Schweitzer tow hook debate on Recreational Aviation Soaring.

Charlie
 
I don’t care for electronic tachs among steam gauges yet I love glass panels. I’ve never liked anything EI has made.

We all have opinions. I changed my Skywagon tach last summer. Mitchell.
 
Can disagree with me if you want. Go ahead and enter in somebody's logbook that you overhauled a tach (or a compass). Not me - I value my license. I don't touch things that I am not authorized to do. I don't even varnish props any more. Yet they stay so shiny . . .
 
bob turner said:
Can disagree with me if you want. Go ahead and enter in somebody's logbook that you overhauled a tach (or a compass). Not me - I value my license. I don't touch things that I am not authorized to do. I don't even varnish props any more. Yet they stay so shiny . . .
Click to expand...

I don’t disagree with you on any of that. I also don’t sign off part installs unless I am sure of its airworthiness.
 
Think about other items we sign off after removal for maintenance. For instance, I sign off items that have been welded by others, as I'm not a welder. I didn't perform the work and I may not have witnessed it but it's legal for me to inspect it and determine that it's safe to install. I sign off the reinstallation of items like these automotive tachs as I can check them for proper operation without using complex or special test equipment.

I have no problem if you don't want to sign them off, just explaining why I do it.

Web
 
There are some things which are best left unsaid and unlogged. Wisdom and knowledge will tell you what they are. In this case, a failure of an antique design tachometer is not a safety of flight item. Even though it is an FAA requirement that one be installed, no one will be hurt if it fails. The owner could if he wished using his electronic tach checker remark the glass of the instrument for his own benefit. Then knowing then what the numbers mean, keep on trucking.

Do not construe that I'm advocating violating the FARs, I'm not. Use your head.
 
Gordon Misch said:
I keep wondering - how is the accuracy of a second, say optical, tach known or verified?
Click to expand...
If your airport still has mercury vapor lights, point the airplane at the light with the engine running and you sitting in the cockpit. Adjust the throttle until the prop blades appear to be stopped. The rpm will be a multiple of 60. So at 600, 1200, 1800, 2400 etc the prop will appear to be stopped. Compare this with the tach.

I've only tried this with the Merc vapor lights. Any 60hz light should work.
 
Point it at a fluorescent bulb. I checked mine once and it was something like 3600 (?) for 2 blade setting. Will recheck later today. Assumes mains running a 60Hz. I check that with my Klein multimeter. In the old days at night stopping the blades per Pete's comments works.

Gary
 
Legally, we are required to make a logbook entry every time we touch anything with a screwdriver. However, we need not keep most records longer than a year. I log oil changes and tire rotations in pencil on the hangar wall.

To me, there is nothing more objectionable than an airframe log (or pile of logs) with gazillions of entries. Our J4 came with an airframe log with every single flight logged. My personal Cub has a "five year" logbook from the early 1950s with ten entries in it! I hate that logbook, but cannot bring myself to pitch it.

I like logbooks with precise compilations of ADs, with page numbers for compliance and signatures, similar compilations for major alterations and repairs with 337 dates, annuals, transponder certs, and very little else. A single "Piper Cub" logbook lasts me a quarter century. And all my tach times - all three aircraft - are airframe time. The J4 (fourth aircraft) has a "Hobbs" style counter, since the AC Tach did not fit.
 
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