Does your r65 tachometer take smoko breaks??

[ambrose78]

My tacho behaves rather erratically and has done so since I came to own the bike.

The symptoms my bike displays:
It'll work fine most of the time, but then for no apparant reason it will either just stop working for a period of time, (or the needle will flick to wherever it feels like) After it has had a moment of erratic/non exisitant behaviour it goes back to normal. Sometimes, even short rides this will happen several times, other days it perfectly all day, even on a 300km long trip.

Thankfully it doesn't seem to affect the opperation of the bike. But after the ICU and bean can gave up the ghost a while back it makes me nervous to see the tacho missbehaving.

I'm wondering if this is normal 'full-of-character' R65 behaviour.

[ultralights]

i have a strange one for ya, my tacho works Ok, just occasionally skips a few hundred RPM then returns to normal, but the weird thing is, when i start off, the glass/plastic cover is clear, but after a 2 hr ride, the tacho is almost totally white! and almost unreadable,  like a small layer of cloud forms in there! yet when i stop, in 5 mins, its clear again.  and the bike hasnt been in the rain now for a few months!

[nhmaf]

It really sounds as if you may have a loose connection or broken/intermittent wire going to your tachometer, Aussie_Pete.   The tachometer's signals come in from the ICU, which gets them from the bean-can/trigger unit.   If you've replaced those (2) parts with good ones I'd first check for  possible intermittent wire connection going from their up along the backbone to the tachometer.   If nothing shows up there, perhaps you've a bad connection inside the tachometer itself?

Ultralight - it is not uncommon for these bikes to collect some moisture inside, especially if they are run in cooler, damper climates.   The small  ~6W bulbs inside usually produce just enough heat to partially evaporate the moisture, but if it cannot get out easily enough it just condenses on the instrument face.   There are a couple schools of thought on this topic, and I've been thinking of doing something on my bike, but haven't decided yet:
1.  Replace bulb with appropriate wide angle white/blue LED with current limiting resistor - the LEDs produce very little heat and are therefore unlikely to cause the tachometer internals to warm up to partially evaporate the moisture.   However, some experimentation is needed to ensure the instruments are well lit, and I don't know if enough moisture would gradually accumulate over a long time to cause long term issues.
2.  Drilling a TINY hole (less than 1mm DIA) carefully through the bezel and just under the "lip" of the rubber sealing ring that goes round the instrument near the top of the face.  In theory, this tiny hole would work like the whistle-hole in your teapot and allow moisture a path to escape, but if the hole is small enough and mostly covered up by the edge of the rubber ring that should prevent rain from getting in there - though it won't stop a steady stream of water from a garden hose.

These are (2) things to consider.   Some people just take the tacho off and leave it in the hot sun for a day or two.  YMMV

[Justin B.]

Pete, the tach would sometimes drop out (just little short blips) on our '80 and running a ground wire between the forks and frame appeared to fix it.  I put an ohm-meter between the frame and forks and noticed periods of infinite resistance depending on where the forks were turned to.  Remember, on a stock setup the forks are grounding THROUGH the steering head bearings.  It's possible that the tach had a flaky ground wire or something so was relying on it's mechanical mounting for a ground which was "iffy".  

You may just have a case of cleaning connections since your tach drop-outs are more prolonged.  Pay particular attention to the connector that plugs into the tach...

[Bob_Roller]

I had a infrequent tachometer issue, it would just 'spike' and then settle down again.

I went through all of the electrical connectors, and found some that were not pushed together all the way, and I found a few 'pins' on the connectors, that weren't secured in the connector, when you pushed the two halves of the connector together, the pin would get pushed out, and have minimal contact with the mating pin on the other side of the connector.

So go through the wiring, and add the extra ground wire as Justin mentioned .

[montmil]

Non-BMW tach on my '81 R65. A TrailTech Vapor digital gauge. The '83 R65 is has stock instruments and they work great all the time.

[Justin B.]

As far as the grounding wire is concerned, Moto-Bins recommends this on R65s to keep steering head bearings from getting etched...

[Bob_Roller]

I'm not sure that etching would be of a real concern with steering head bearings, as they move through such a small arc, that the outer race gets a 'divot' in it from the pounding it takes, just like the swing arm bearings.

[Justin B.]

I was under the same assumption but Moto-Bins apparently feels it to be an issue on dual-shock R65s...  I'm pretty sure this has been pointed out before but this is from their web site "Tech Tips":

"Steering Head Races on R45/65, R80ST models can often suffer premature failures, their outer races showing regular dark lines where their rollers have made contact. These lines are the sign of electrical erosion, probably due to tracking across the tachometer's ignition coil connection on the printed circuit board to the steel case of the instrument. Make sure that you earth the upper fork yoke to the main frame earth below the fuel tank, to provide an alternative path."

[nhmaf]

I also added a ground wire on my R65 (see my dual Fiamm installation article in the wiki).  Normally the electrical arc current corrosion isn't much of an issue with electrical machinery unless you start getting up there in voltage and current.  We had issues with bearings in electrical motors in industrial robotics systems if ground straps weren't properly attached.  But, the airheads have been known to have grounding issues with the instrument panel, and BMW doesn't seem to put in spare/redundant grounds, so I figure it is just a bit of insurance.  If it also prevents low level corrosion of the bearings that is another benefit.   I would recommend doing it - it is quite simple to do.

[Lucky_Lou]

i have a strange one for ya, my tacho works Ok, just occasionally skips a few hundred RPM then returns to normal, but the weird thing is, when i start off, the glass/plastic cover is clear, but after a 2 hr ride, the tacho is almost totally white! and almost unreadable,  like a small layer of cloud forms in there! yet when i stop, in 5 mins, its clear again.  and the bike hasnt been in the rain now for a few months!

Mine works all the time but did tend to mist up badly when i first got the old girl back on the road. When ever we have a sunny day i strip the cowling off remove the wirering plug strip the bottom black plastic cover off(3 screws)and let it breath.....it has improved dramatically pity i dont live in Arizona it would have cleared by now.
Lou

[Bob_Roller]

When I lived in Chicago, it was quite common to get a bit of fogging on the inside of the indicators, after a wet spell, or when the bike got washed.

Since moving to Phoenix, the bike may get ridden a few times a year in the rain, and it gets washed once every 6 months , whether it needs it or not, no fogging problem in the last 16 years .

[Barry]

My Tacho works perfectly but mists a little same as all the rest. A small silica gel bag helped for a while.

I've always been curious about the moto-bins comments on grounding. How does the head light work if there is no common ground wire between frame and forks?  Looking at the wiring diagram I can't even see a reference to the tachometer except for bulbs.

Anyway just been out to the garage and  put my trusty Model 8 AVO  between frame and forks. Result was zero resistance and not the slightest variation  from lock to lock.

The only thing that I can think of  that might cause the errosion is that the LT side of the coil will rise to serveral hundred volts when the point open.

[Lucky_Lou]

My Tacho works perfectly but mists a little same as all the rest. A small silica gel bag helped for a while.

I've always been curious about the moto-bins comments on grounding. How does the head light work if there is no common ground wire between frame and forks?  Looking at the wiring diagram I can't even see a reference to the tachometer except for bulbs.

Anyway just been out to the garage and  put my trusty Model 8 AVO  between frame and forks. Result was zero resistance and not the slightest variation  from lock to lock.

The only thing that I can think of  that might cause the errosion is that the LT side of the coil will rise to serveral hundred volts when the point open.

there is a ground wire to the lights and horn its the brown one i think....will have to check the diagram to be sure though
Lou

[Bob_Roller]

The head lamp has a brown ground, or earthing wire on the 3 pin connector that goes on the lamp itself.

I don't know what version of the wiring diagram you are looking at, but the connector for the tachometer has the coil input wire at pin number 5, and pin 8 is a ground wire for the tachometer, battery charge ,neutral indicator and oil pressure light .

Pin number 2 is the ground wire for the high beam indicator light, and internal lighting for the indicator.

So as far as I can tell, there are ground wires to all circuits in the instrument cluster, and all lighting circuits for the front of the bike, and the steering bearings aren't used as an intentional pathway to ground, at least in the '81 model year R65.

All of the ground wires terminate and 'ganged' together at a threaded fitting around the relays under the tank, on the '81 and later bikes, I believe the '78-80 model year bikes used the front ignition coil hold down clamp as the ground or earthing point for the bike

This may be true on earlier bikes, I have never seen a wiring diagram for the earlier bikes.