The mechanism was whining very loudly and it ended up vibrating one of the small faceplate screws out. The needle was also all over the place. Checked my cable and it’s properly lubed and functioning correctly. I took the tach apart last night and tightened all the screws up and put it back together. It seems to be working now but sill makes some noise.
Did you lube bearings on the 'bell' before reassembly?
When my tach had issues it was caused by the boss that the cable connects to coming loose from the rest of the frame. I got it all back together and working with a few layers of JB weld. Now its not half bad. There are lots of videos out there that may help.
Simply put, the cable spins a magnet, the magnet rides inside a small steel bell shaped part that's connected to the needle on the face. With your engine running the cable spins the magnet which couples to the bell via magnetic field, raising the needle to indicate engine RPM.
Its a brilliantly 20th century (or earlier) design, all mechanical and generally reliable.
Be careful not to use solvents that can get onto the tach face, that paint damages easily.
On mine I cleaned out the old lube with brake cleaner and re-oiled with 3in1 oil on a toothpick. Then I had to JB weld the part the cable threads onto back in place. This part contains the bearings, shaft and magnet assembly so alignment is important or the magnet rubs the bell. Mine had worn through the bell in one spot, but its good now after no less than 2 layers of JB which are squashed in place by the gauge cup.
Mine came out pretty ugly but it works and I learned a lot.
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