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Bought a '77 kz650 that had been sitting and hasn't run in 15 years or so. After a lot of clean up and rebuilding this and that, I started it up and got it running. 
Noticed the tachometer wasn't working. 
pulled the cable off today. Seemed fine. Removed it from the bike put it in the tachometer. Gave it a few spins and the needle jumped.
took out the worm gear, everything looked fine...
Reinstalled the gear and cable but left it out of the tachometer. Started the bike up. Nothing. Cable wasn't spinning at all. 
Tried spinning the worm gear when it was installed. Felt like it was catching on something but could wiggle it free and spin it.......

Opened up the valve cover and found this.


Curious if anyone else has experienced a camshaft missing it's teeth? Funny thing is the worm gear doesn't have some much as a scratch in it

Well, there's your problem! I have not seen that before.

I do have a concern, though: what happened to all the metal bits that got loose?

Nerdy wrote:

Well, there's your problem!

I have not seen that before.

I do have a concern, though: what happened to all the metal bits that got loose?

And what caused it to strip ?????

That's what I was wondering too. No way to get a hold of the previous owner as they have passed. 

Guess I'm going to have to go on an engine tear down hunt for metal pieces.

Worm gear honesly doesn't even have a scratch

These old machines always have a story 

Wookie58 wrote:

And what caused it to strip ?????

That is a fantastic question as well. I was thinking the worm gear might have gotten bound up (overtightening to stop an oil leak? it got off-kilter somehow?) but if that happened it seems like there would be at least some noticeable damage to it.

Maybe it was a metallurgical defect?

Could be that the previous owner replaced the worm gear trying to fix the problem ?

Wheelhop wrote:

Could be that the previous owner replaced the worm gear trying to fix the problem ?
 

That's an excellent point. If the PO replaced the gear (and maybe the cable) and the tach still didn't work, he might have given up.

Or he pulled the valve cover and saw the damage and then gave up.

That is why I always remove the complete tach drive assembly when I go to install the exhaust cam.
That way I never worry about bending the tach drive gear or worse deforming or
breaking the spiral gear teeth machined on the exhaust cam. I have seen that damage before on many four cylinder KZ's in the past. Some say just wiggle the tach drive gear as you tighten down the exhaust cam. I always found it easier just to pull the whole tach drive unit.

Notice whole tach drive unit pulled.
 

Dr. Gamma wrote:

That is why I always remove the complete tach drive assembly when I go to install the exhaust cam.
That way I never worry about bending the tach drive gear or worse deforming or
breaking the spiral gear teeth machined on the exhaust cam. I have seen that damage before on many four cylinder KZ's in the past. Some say just wiggle the tach drive gear as you tighten down the exhaust cam. I always found it easier just to pull the whole tach drive unit.


 

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