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1982 R100 - new bike to me. Bought the bike as a non runner, have got it cleaned up and running fine, but upon first run noticed the Tach is not functioning.

Is there a test procedure to decide if the problem is the Tach or the power feed from the ignition?
Anything obvious that I should be checking first?

I had repaired the odometer for its normal failure but had never thought to look at the Tach before I started the bike. Not something I have had a problem with before.

First thing to do is remove the tacho and make sure that the needle isn't obstructed from moving. I had one of the small bolts in there come loose and cause that.
Then check coil connections....or vice versa.

Grant will be watching. His tacho has been playing up lately too.

Thanks Steve. The needle is fine and I have verified no breaks in any wires.

Tomorrow I will swap the whole assembly to another bike and see if there is any change.

Looking at the circuitry, I am sure there isn't an easy amateur fix.

Chris

Chris, re: tach pooched....bummer. I too have just redid an 82 R100 "under the plywood, behind the drive shed" redo this winter. When I finally got it up and running (on the bench) the tach worked fine.

Yesterday was warm enough finally to do a road test. Started up, tach went up to 2000 rpm and never moved after that. After road testing (adjusting new steering head bearings etc) the tach stayed at 2000pm. So, pulled it out to see what might be problem. Wiring seems OK and no needle obstruction that I could see although if rotate needle it just sits there - no return. Is there a return spring on shaft like the old mechanical ones? Don't see one but my eyes are fading in the light.

I did have instrument pod off doing the steering head etc. Don't think it had ever been off in 30 years. All connectors in 12 pin connector looked in great shape. No corrosion that I could see. However upon reassembly it was a stuggle to get it back on. Didn't slide in easy like other ones...hmmm...wondering if could be pin connection here? Maybe ground not engaging correctly or the other 2 connectors. Telltales all work fine so investigating a bit further.

Also have another tach I can swap out but I'm thinking its electrical connection at the 12 pin connector...I'll let you know what I find...I'll check and see what you come up with.


Bob

PS: She ran well for first outing..and no more ol leaks.new pushrod tube rubbers, gaskets etc...she will be my "backroad beauty" since the sale of the GS...she ain't purdy but mechanically she's in top form for now!

Also, every post in the housing was cracked or split so epoxy here we come.

Those connectors were a bad idea. We got a new bike that had a folded over tab in that connector. We had to fix it before selling it to a customer.

Most seemed to require a lot of pressure to install. Good luck.

In the instrument pod itself the connector pins connect to the flexible printed circuit. That connection can go bad. I recently spent hours fixing some of the connections on my '76 R75/6. The failed connection was was why some of my dash lights weren't working. The thing that self-embarrassed me was that I had a clue that I hadn't paid attention to. It was an old pin-to-printed circuit connection that I had repaired myself well over 10 years ago.

I've fixed the connections a couple of ways. Both involve scraping away the plastic film on top of the circuitry near the pin. In one case I wrapped a light piece of jumper wire around the base of the pin and soldered the other end to the printed circuit path. Another time I made a soldered connection without the jumper wire.

Ken

Update for Chris..

This afternnon swapped out 82 tach with known good one and it worked fine. So electrical connections were fine at big sqaure block connector and internally.

I did compare the 2 tach mechanisms before the swap. The not good 82 tach, when I move the tach needle up to say 3-4000rpm range would not return to zero whereas known good tach did zero back. It seems to me the return spring or dampening spring may have gone wonky or become disjointed somehow. I recall a few old mechanical tachs I've seen in the past had the same problem with the return/dampening spring and unrepairable by me IMO so junked them. I think this is problem here.

Tonight or maybe tomorrow when my hands are steady and eyes bright (I'll get my jewellers magnifiers on) I;ll see if the spring or maybe mounting post for spring is pooched. Doubt whether repairable but at least I'll know.

So do the swap and if good then that rules out poor electrical contacts in some areas.

Good luck...let us know how you make out.
Bob

Fixed the broken tach today.

Couldn't see any problem with return spring but noticed plate the tach face bolts to was very loose. Removed needle (just about fell off) removed 2 screws holding tach face. The 2 little screws holding the mounting plate were practically falling out. Plate was just wobbling around. Tightened them up, reattached dial face and needle and, voila, return springs work fine returning needle returns to 0 every time!

Repalced it into the guage holders, connected electrical connections and everything was fine, I suspect the backing plate had allowed neddle to just about disengage and when realigned the needle sat more securly on its shaft, So lucky, easy fix.