pics of the inside of tachometer

[who444444]

I had the screaming tach problem and lube was not fixing it. so I took it apart to see what was up.
I thought I would find gears and such but no, just a revolving disc using magnetic induction? or?
whatever I see the only thing that could be making the noise was the bushing the shaft with disc was spinning in. I got some wheel bearing grease into it by
treating it like a wheel bearing hand packing job, just real tiny amounts. reassembled and noise is gone.
Here are some pics to show anyone who has not seen the inside of their tachometer.
and here is a link to bad quality youtube of tach running showing inside works.

https://www.youtube.com/watch?v=_Ea4G7e ... ata_player

I now think I could of gotten grease up into bushing without even removing tach from bike. oh well
dave

 

[dan filipi]

It's good to know that's the only place the noise can come from.

I suppose the Speedo is the same eh?

 

[joedrum]

never seen it before ...cool

 

[Ansimp]

:good:

 

[dan filipi]

Who4444, could you see why the needle would 'hang'? That's what mine is doing.

 

[AApple]

Speedo design is basically the same, except it also has a gear drive to operate the odo & trip meters. :yes:

speedo 008

• AApple
• Sep 4, 2013

A needle hanging up in one spot would be either the needle is bent, and hanging on the gauge face, or the shaft the needle is attached to is hanging in the bushing. There is NO direct contact between the magnet(drive) and the cup(driven) portions of the gauges. There is a specific air gap between the two parts. As the magnet spins with the tach(or speedo) cable, the magnetic force causes the metal cup on the needle side to move at a predetermined rate, depending on the speed of the drive magnet, the air gap, and the strength of the magnet....the faster the magnet spins, the higher the needle sweeps.
On gauges that jump, or peg out, it is usually metal particles inside the gauge housing sticking to the magnet, and reducing the air space between the mag and cup. Get enough crap in there, and the two parts touch. Since the magnet spins all the time, when the cup touched, or locks to the mag, the needle has no choice but to go along for the ride. And, since the needle is not designed to spin all the way around the gauge face, it will peg out....assuming there is a peg on the gauge face to stop it....not all gauges have stopper pegs, but most do.
If the bushing that the shaft runs in is worn enough, it can allow the magnet/shaft to hit the cup, and make the needle jumpy.
Gauges 101 class is now out. Please turn in you exams on the way out. :read: :smilie_happy:

 

[dan filipi]

Well dat 'splains it pretty good.

Mucho Gracias Signor.

 

[who444444]

+1 on Aapple's post dan. much better info than I could give you. Now I know what and how it works. lol
dave

 

[AApple]

I fergot to mention the shaft/cup part that the needle runs on is also spring loaded, or has some form of tension on it. This helps keep the needle steady, and also brings it down to rest at "0". :blush:

 

[joedrum]

gee never to old to learn something