Weird tachometer problem solved (finally!)

[EdHut]

Hi All,

Just want to report the weirdest (in my book) tachometer problem that I have been chasing the last few days.

Since around september, my tachometer was not working properly. The needle would hardly come from it's place, and when it finally did (after repeatedly revving the engine to higher regions), it would return very slowly, sometimes even stopping at about the 2000 rpm mark.

After reading some posts on this great forum I started testing all the wiring, trying a bypass of the black/purple wire that drives the tach, all to no avail. Also cleaned my ground strap (didn't look like it needed to be, be it couldn't do any harm anyway).

Finally I decided to pry the tachometer open to get a look inside. This was the first time I did something like that and I had been putting it off for quite some time. After removing the rings and glass the needle seemed to move without any problem at all (wiggling the tachometer in order to bounce the needle a bit). It didn't do that before; how can that be?

Only then I noticed the tiniest piece of dirt sitting exactly at the top of the hub(?) to which the needle is attached. This tiny speck must have been just touching the glass and thus causing friction.

I just tested the tach and it works like a charm again.

Now I ask all the Warrens, John Walkers and Supermen of this board: how the heck could that dirt get in there in the first place? It must have been a design error