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Zeroing and re-marking an AC Cub Tachometer

P

Philly5G

Registered User
England
Having changed the engine in my 12 for a Zero Timed O235-C2C I need to re-mark the tacho with the 2600 redline and I'd rather do this on the instrument face, rather than the red tape on the glass face that I've (temporarily) done as I couldn't figure the best/non destructive way to get the bezel off

PA-12 Tacho.png

can someone please explain the best/safest technique for this please?

Also, as it's a Zero-timed engine, I'd REALLY like to zero the time on the tacho counter too 8) can this safely be done and if yes, HOW?!!!!

Thanks!!

Philly
 

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Just buy a new one and have it marked properly. You'll have a lot of time into something you should not do unless you are an instrument shop, it'll still be old and will likely not be accurate anyway. Can it be done? Yes. Would I do it? No.

Normally these intrument bezels are "Bent" around the flange of the case. Or, they are newer and the bezel screws on with countersunk screws. To get the bezel off you would need to pry the bezel and do your work, then rebend the bezel back around the case flange.

In other cases, you may be able to remove only the glass by removing the snap ring holding the glass in.

My point. There is a lot to easily get wrong, and a lot that is difficult to get right. YMMV....
 
Grant said:
Just buy a new one and have it marked properly. You'll have a lot of time into something you should not do unless you are an instrument shop, it'll still be old and will likely not be accurate anyway. Can it be done? Yes. Would I do it? No.

Normally these intrument bezels are "Bent" around the flange of the case. Or, they are newer and the bezel screws on with countersunk screws. To get the bezel off you would need to pry the bezel and do your work, then rebend the bezel back around the case flange.

In other cases, you may be able to remove only the glass by removing the snap ring holding the glass in.

My point. There is a lot to easily get wrong, and a lot that is difficult to get right. YMMV....
Click to expand...

Thanks Grant, a common sense and pragmatic approach as always :up Just looked them up on Spruce and not as expensive as I'd thought, looks like they can be customised with the RPM range markings and preset to a starting number of hours to match the current/projected engine hours too 8)
 
What Grant says.

Get the tach ordered up marked and set exactly the way you need it. Then drop it into the panel and be done with it.

Web
 
coxcub said:
Here's your man - Bruce irvine - https://airtroninstruments.wordpress.com/
Only just up the road!
Frank
Click to expand...

Thanks for this Frank, but!! - I tried to call this company a few weeks ago when I was looking for someone to fix/refresh the original Cub combined Oil Pressure and Temp gauge. The phone number led me to a very pleasant chap, who, with infinite patience, told me he was forever getting phone calls for aircraft instrument repairs, but it was a wrong number!!! I've also tried to email them, but no response!
 
Maybe just send out the old tach -- Rudy A/C Instruments in AR charges about $150 to overhaul a tach.
I talked to them not long ago about OH'ing & re-finishing the face of an airspeed indicator,
and I think they wanted an extra $75 or so for the refinishing.
So probably $225-250 for making it like new with the correct markings.
 
That's what I would do if the last remaining "Speedotach" business in San Diego ever goes out of business. These are auto speedometers converted to aircraft tachometers, and the auto shops have the parts and expertise. But Rudy's prices are inline, and they do my gyro instruments.

Now, a recommendation: Figure out your airframe time, and put that in the tach window. Then do a subtraction for your engine log entries. Tach time approximates airframe time, and makes airframe log entries so much easier!

All my airplanes have the tachs set that way except the J4. It doesn't have room. I have an hour meter in it, but hour meters are nowhere near airframe time. In the olden days, folks logged each flight in the maintenance log. Yuk!
 
Keep in mind that the cost of a new tach will be $500 to $600 USD plus shipping one way across the pond. If you get one overhauled, it's the cost of the overhaul, plus two trips across the pond (if not able to be done locally).

In rule to live by with used parts; if the cost is around half price of new, get the new.

Web
 
And, understand that a new tach can read almost 100 rpm off, and still be “legal”. I went through that and decided ‘twas better to go electronic. And, yes, that new tach read 80 rpm low.

MTV
 
Spruce lists the Electronics International, R-1 tach for $448 USD. Install that and get rid of the tach cable, and probably never have to touch it again, after installation.

Web
 
I flew the other day in my 11 and when I did my log something didn't add up I lost over two hours from my last flight thought I must have made a mistake, Yesterday watched the tach rpms were good but tach was removing time so lost a few more hours yesterday and it was subtracting time at a 3 or 4 to 1 ratio if this keep up I'll have a zero time engine before I know it. Has anyone had or heard of this happening? Tach was new 1075 hours ago.
 
Douten said:
I flew the other day in my 11 and when I did my log something didn't add up I lost over two hours from my last flight thought I must have made a mistake, Yesterday watched the tach rpms were good but tach was removing time so lost a few more hours yesterday and it was subtracting time at a 3 or 4 to 1 ratio if this keep up I'll have a zero time engine before I know it. Has anyone had or heard of this happening? Tach was new 1075 hours ago.
Click to expand...
Did you have a tail wind? :wink:
 
Douten said:
I flew the other day in my 11 and when I did my log something didn't add up I lost over two hours from my last flight thought I must have made a mistake, Yesterday watched the tach rpms were good but tach was removing time so lost a few more hours yesterday and it was subtracting time at a 3 or 4 to 1 ratio if this keep up I'll have a zero time engine before I know it. Has anyone had or heard of this happening? Tach was new 1075 hours ago.
Click to expand...

Is this a mechanical tach with a cable? Obviously sounds like the time counters have somehow switched themselves over to the opposite rotation direction, whilst the RPM mechanism is still correct. Have you removed or done anything with the tacho? Particularly around the time when the hours stopped making sense?


Sent from my iPhone using SuperCub.Org mobile app
 
Mechanical drive c-90-8 so tach is counter rotating haven't had anything apart almost seems like it's disconnected and just vibrating to lower time. I have a new one I just installed in the panel of my new project just hate to put it in and buy a another one. May even have the old one that I replaced on rebuild laying around someplace so I could replace and send this out for repair.
 
Douten said:
Mechanical drive c-90-8 so tach is counter rotating haven't had anything apart almost seems like it's disconnected and just vibrating to lower time. I have a new one I just installed in the panel of my new project just hate to put it in and buy a another one. May even have the old one that I replaced on rebuild laying around someplace so I could replace and send this out for repair.
Click to expand...

Maybe try whirling the cable with an electric drill, so there’s minimal vibration and watch what happens?


Sent from my iPhone using SuperCub.Org mobile app
 
TurboBeaver said:
Could also just install an 0320! Problem solved........[emoji36]
Sorry old boy just couldn't resist.....[emoji41]
Cheers and all the best .
E

Sent from my moto e5 go using SuperCub.Org mobile app
Click to expand...

Ha ha ha!!!! Thanks TB!!

I've just got to the end of the "Lycoming Reciprocating Engine Break*In and Oil Consumption" Service Instruction No. 1427C procedure (and proceeding with the 2250/2350 cruise until break-in) with the new O235-C2C replacing the O235-C, with a total of 3.5 flying hours and there's an absolute and noticeable improvement in power and handling already, although some of which will no doubt come from having the propeller overhauled, the first difference being that the tail lifted itself within the first few feet of the take off run which took me by (pleasant) surprise after being used to pushing forward to lift it and the climb performance is spectacularly better, obviously early days but looking like 8-900' per minute (on each flight) rather than the 5-600 fpm before. Cruise speed is similar to before, which I guess you'd expect

#Wow!!!
 
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