Bouncing R65 Tachometer

[Bbelk]

I posted this at the Boxerworks fourm and it was suggested I try here.  The little warning light I mention is the small round one on the far right at the end of the needle swing.

I have a 1979 R65. I have put about 5,000 miles on it since I got it, 16,000 total, and today a new problem showed up.

While crusing at about 70, the Tach just started climbing in a jerky fashion up to the red line and I think the little warning light came on for the first time. Then it just started bouncing all over the place mostly high. It seemed to recover at an idle and held until I spent a minute or so above 60 and then it went wierd again.

Any thoughts would be appreciated.

Thanks
Brad

1975 R90/6
1979 R65

[nhmaf]

Most of the time when I've seen a jerky tachometer needle it has been due to a
frayed or worn out cable.   But, I haven't seen this sort of thing cause the RPMs
on the tachometer to go up higher and into the warning zone.   It might be time
to consider a repair/rebuild of the tachometer, but I'd check the cable out first,
at least on each end, for signs of wear, rust, frayed cable strands, etc. as that it
the easiest and cheapest to replace, as a first step.

There are some other folks here with 79 models, so I'm sure that you'll get some
more useful input.

[nhmaf]

Another thought - can you make it do this while sitting still in the garage and revving the engine ?
If it will exhibit this same behavior while sitting still, and you have a multimeter/voltmeter, I would
get to the terminal connections at the back of the tachometer and check the voltage levels - I don't
have a 79 so I'm not sure what color wire/terminal to look at for the +12V power.   If you see
the voltage level jumping around with the needle swings, then it is possible that your voltage regulator
isn't working properly, or something else in the charging circuit.    If you are going to be running the
engine for more than a couple minutes while in the garage, it would be good to get a big fan from
your front porch/window/ where ever you keep fans to blow some air from the front of the engine,
if you aren't already aware of this.

Does your "Generator" light still work normally ?   It would/should light up at idle, but go out as RPMs
increase.    It will light up to show a low voltage condition, but won't do anything if the voltage is perhaps
too high.

At least, these are some things to check that don't involve taking the tachometer apart, which could get
more "involved" !

Good luck and let us know if you find out anymore info.

I'm sure others will have some more wise suggestions.  

[Bob_Roller]

The tachometer electrical signal comes off of the ignition coil,  the wiring diagram shows a .75 sq. mm black wire from one of the coils to pin 5 of the tachometer electrical connector. You may want to check the condition and security of the metal connections at each end. The wire also goes through a 6 pin connector between the coil and tachometer, if you can locate that and check it as well. From what I can remember, there is a printed circuit board inside the tachometer, you may want to look inside, and see if you have any corrosion or possibly bad solder joints. I don't recall anybody taking a tachometer apart before.

[nhmaf]

Oops, that's what I get for not drinking my coffee in the morning..
I read "tachometer", but thought "speedometer"....

 

I think that I'll go make that pot of coffee now before I try to vacuum
the lawn or mow the living room carpet !
<This new allergy medication is definitely hindering my functioning today - I'm
going to stay home and stay away from motorcycles till it wears off !>

[Bbelk]

New information:

1)  Today while parking the bike in the garage I notice the headlight turns off and on when I turn the handle bars back and forth.

2)  I just had my steering head bearings replaced.

I don't know if these facts help, but I will be looking for something lose.  I can live with a failing tach, but not a failing headlight.

Answers to questions:

Yes it the tach will act up at high revs with the bike sitting still and the generator light acts like it always did.

I will let you know what I find.

Thanks
Brad

[Justin B.]

Run a ground wire between the bike frame and the forks.  I recommend this because after greasing the steering head bearings on our '80 the tach acted funny, usually not reading high enough and in a very narrow range.  Adding a ground strap fixed that and the more I think about it I vaguely remember the kid maybe mentioning the LED coming on once or twice.  I really can't remember as I didn't really ride the bike.

[thrang]

Its always worth earthing the yokes as it stops any electrostatic corrosion on the head bearing's and extends their life considerably.

Not got a clue about the tacho problem though.

[nhmaf]

We had a good thread on the old board about connecting a ground wire from the chassis
frame to either the top steering yoke or the back of the headlight bucket or headlight
bracket.   Make sure that you get down to clean metal and use a biting star washer
to keep things on tight.  you can touch up paint the frame, any exposed bare metal
after its all done.  A good spot to find a place to attach at the frame is on the front
side of the frame where the original horn is mounted (on 81-84 bikes, anyways).

Use a wire that is at least 16 gauge, 14 gauge preferably.  That should certainly handle all the return
current from the instrument pod and headlight with no problems.   IF you have a good
multimeter, you should be able to check the resistance from a bare metal spot from the top
yoke or headlight bucket, back to the frame, and see the resistance go up&down as you turn the
handlebars from side to side.   After you hookup the ground wire, this resistance should
not change and be much less than 1 ohm.

It definitely sounds like you don't have a good/adequate ground to the instruments and
headlight.   This is fairly common on these airheads - and the fact that the return current
was going through the steering bearings contributed somewhat to their demise.
After you get this done, let us know if you still have problems with your headlight or tachometer.

Good luck !

[Bbelk]

Bam!

And the gold star goes to Justin and others voting for a ground issue.  Things started going down hill rapidly on the way home.  The first thing I noticed was that it would not start in gear.  It had to be in neutral.  Part way home, the turn signals quit  and then the horn got weaker and finally quit.

With no headlight or horn at all, I grounded the front forks - nothing.  The voltage from the positive to the motor was 13 volts and from the positive to anywhere on the front forks or cluster it was 13 volts.

After un plugging and plugging everything to no avail, I noticed I could push on the whole loom and everything came on.  After 30 minutes of this, I finally see that the front coil is hanging free.  The metal tab it mounts to off the frame has broken off.

Sure enough the entire wiring harness seems to ground through one big fat brown wire attached to the front coil.  I made a jumper from the front to the back coil for a good solid ground and then hose clamped the coil back to the frame just like I did on my 1963 Econoline van and I am back in business.

German engineering still confuses me.  What they get right and what they get wrong.  Oh well.

Thanks for all the tips.

Brad

[Rob Valdez 79 R65]

[size=36]I'm Sorry, Brad[/size]  


Yeah, this is such a common failure on the '78-'80 design, that had two separate coils.  The front coil mount always breaks, eventually, and the MAIN EARTH WIRE for the entire main loom is bolted to the coil bracket that is in turn bolted to the piece of bracket that just came loose from the backbone of the frame.


I drilled a hole in the metal "tray" for all of the connectors, and sanded down the paint where the wire connector would touch.  Some dielectric grease and a 10mm nut & bolt and you are back in business.

Extra long hose clamps for your front coil.