Stranded

[Yikes]

The old ‘82 has been running great but over the past several months, very happy with its new overhauled heads, but it has developed a problem that has progressed to the point of leaving me stranded more than once.  There are few things more embarrassing than having to call someone to give you a ride home because your bike’s broken down.  
Starting is no problem but soon after it gets nice and warmed up, say 5 or 6 miles, it’ll just die.  The starter will turn and run, but it won’t fire up.  After wait of 5 -10 minutes, it will start and run fine for 3-4 minutes then start to sputter out and finally die, not to be started again.  While it is in the throes of sputtering, the tach will wave madly up and down.  Again, the starter will turn and turn, but no life.  Pulling a plug, and grounding it against the cylinder reveals no spark at the plug, in spite of the new coil.  After turning the engine over a few times in this lifeless state, a spark induced by flipping the kill switch off and on will occasionally result in a backfire.   The only way I’ve found to get it going again is to remove the battery and charge it up, replace it and all is fine again  -  for a while.  When I place the battery on the charger, it always seems to be very, depleted, sucking down juice in the 6-10 amp range for 20 minutes or so before it starts dropping down to the zero range.
Wondering if anyone here has had this experience and found the source of the problem.  I am getting ready to do some homework in my Haynes and Clymer manuals and see what I can glean from the electrical sections of the Snowbum chronicles.  The obvious and fatal symptom is no spark at the plug.  I know the battery is good and the coil is good and there is power to the coil   I was going to re-do heat sink paste in the ignition control unit, but it is firmly riveted to the heat sink, and I don’t really feel that overheating of the ICU is the problem.  
Thanks for any insight or advice.

John M, Roadside Attraction

[Bob_Roller]

It sounds like an ICU problem, personally I wouldn't ride it until it's repaired.

My best suggestion, would be to run the bike in your garage stationary, with fans blowing cooling air over the engine.

To try and duplicate the failure, if you can duplicate it, have a can of electronic 'spray freeze' ready,  remove the tank, and spray the ICU to where it is cold, and see if it you can start the bike, there's enough fuel in the carb float bowls, to run the engine for a couple of minutes or so.

The heat sink on my ICU isn't riveted to the ICU, you could try to drill off the rivets, apply heat sink paste, and then use pop rivets to secure the two parts together again.

After thinking about this for a few minutes, I just remembered that the Hall Effect vane sensor in the ignition canister, commonly referred to as the 'bean can' under the front cover of the engine, has been known to cause problems like this.

You could try and remove the cover from the ignition canister, and try the same thing with the spray freeze on the Hall Effect sensor.

One last but quite remote possibility, can be a faulty tachometer, the ICU sends a signal to the tachometer to operate it.

If nothing else can be found wrong, remove the electrical connector from the tachometer, and see if it helps.

[Yikes]

If the freeze spray test on the ICU gets things going again, does the ICU then need replacing?  

Would riding the bike risk seriously damaging something?.  I know that that I can replicate the problem by riding it.  A trip up to Radio Shack and home for a can of spray is just about the right mileage to send it into it's zombie state.

[Bob_Roller]

I would say that it's a good possibility the ICU is faulty, but before I spent money on a new component, I'd try disassembling the ICU and heatsink, and see if cleaning the mating surfaces, apply a little heatsink paste, and then reassemble it, reinstall it on the bike, and see if it has solved the problem.

I prefer the cheap method, if I can get away with it !!!

You won't damage the bike, but if the bike quits at the wrong time, you may get 'damaged' !!!!

[Justin B.]

The ICU may be overheating and "shutting off" but that doesn't explain your charge issues.  Remove the ICU and (especially if the heatsink compound is absent or dry) clean the mating surfaces and apply fresh heatsink compound.  If the compound is gone, or dried out, there will be inadequate heat transfer between the module and it's heatsink shich could lead to it running hot.

[montmil]

The ICU is supposed to be bolted to the aluminum heat sink component. RadioShak has the heat sink material in a small tube at a very reasonable price.

Suggest you reinstall the ICU to the heat sink with small bolts & nylok nuts. Snug it down but be careful as over tightening can crack the ICU's plastic mounts.

Another possibility is that the Hall sensor in the ignition trigger unit, aka: Bean Can, is in a failure mode. That happened to my '81 R65. Since you mention the "backfire" when you toggle the handlebar kill switch and, if you're getting a spark with the plug out and grounded to the cylinder while you toggle the switch, the coil and ICU unit are functional.

Check the heat paste first. I just re-did the goo on both my R65s and both were dry and dusty.

The ICU is common to many German scoots and cars. The BMW part is pricey. Check this source for the same part at a much better price.
https://www.autohausaz.com/search/product.aspx?sid=melr1b451hriy445yc1vyzu4&makeid=800026@VW&modelid=1280348@CABRIOLET%20%20&year=1986&cid=25@Ignition%20Parts&gid=7172@Ignition%20Control%20Unit/Ignition%20Control%20Module

The battery drain is a concern. No good ideas right now.

Monte 

[Yikes]

Well there's good news and bad news here.  The bad news is that, although the rivets holding the plastic ICU to the metal heat sink were easily removed, when I separated the plastic from the metal, half of the printed circuit inside went one way and half went the other.  The good news is that when I reinstalled it, it turns and turns and doesn't start just like it does when it is in it's zombie state, proving scientifically and without a doubt that the ICU was faulty and needed to be replaced.  And even thought the beer I'm drinking now only comes half way to the top of the glass- it's half full!!

Looks like the old Mädchen is going to stay parked for a while while I procure another ICU. Monte, thanks for the link to a less pricey replacement.  $35 sure does beat $155 by a long shot!  Fingers crossed.....

John M

[Bob_Roller]

Just for informational purposes, does it look like the heatsink is bonded to the ICU with some sort of adhesive?

Or has it corroded with time and the two pieces have become one with the universe ?

In your opinion, is this something that should be attempted or not ?

[Justin B.]

Or, if you get by a Pick-A-Part that stocks a lot of European jobs you might get one for next to nothing.  The module looks just like the one in some Bimmers and Volvos...

[ambrose78]

I had a pretty similar thing happen to my '81 a few weeks back. Mine was combination of 2 problems. ICU was fried and sending out random sparks and therefore causing erroneous backfiring. And the Hall effect sensor had also given up the ghost which was why mine stopped completely. As others have mentioned yours sounds like the ICU.

There are 2 diagnostic tests you can do to check the function of the ICU and the bean can.

Bean can test
1. Remove plug and ground
2. Make sure battery is disconnected, remove front cover of engine
3. Take off the bean can from the front of the camshaft. leave it plugged into wiring harness
4. Reconnect battery and turn ignition on
5. Rotate  mechanism by hand and check for sparks - there should be 2 per bean can revolution.

The other test is to check the ICU is functioning properly. Carrying on from previous test

1. Disconnect battery again
2. Unplug the bean can electrical connector
3. Find a paper clip or similar conductive material and wedge it into the [size=12]middle[/size] pin of the electrical connector (the outer two are the 12v +/- the middle is the signal wire). Find an area to ground the pin to. I used the engine casing. Whatever you do, don't use the diode board!!
4. Reconnect battery and turn ignition on.
5. periodically ground the paper clip. Every time the clip is grounded a spark should fly. If no sparks, double check the spark plugs are grounded. If still no sparks it is probably ICU. or Coil. Though it would be wise to check the outer two wires with a multimeter to make sure power is getting through.

If it is sparking when the paper clip is grounded then your hall effect sensor has died. Fix it yourself as BMW wanted to charge me nearly $800 for a new bean can and you can the sensor pretty easily for around $20.

6. Turn igniton off, disconnect battery. Replace whatever is necessary. Go for a satisfied ride to enjoy your handy work

[larstorders]

If the ICU was riveted to the heatsink I think that unit may well have been salvaged from a car. As you have discovered replacing heat transfer paste ain't possible on these. Suitable replacements are available from 1980s VW Golf Mk3 s and Audis etc of the same period as described on Snowbum's web site. I use one myself and at just a couple of quid each, keep a spare one zip tied under the tank. And there's another thread somewhere about an R65 with a similar problem .
Good luck.

[Yikes]

I finally got to the bottom of the electrical problem that was making me a roadside attraction.  Turns out that it was the beancan.  Looking back over all the related postings, I see that the tell tale sign was the tach reading that dropped to zero during the pre-failure sputterings.

I did not muster the initiative to perform sensor-replacement surgery on my beancan, but I managed to win one from an R100RT on ebay.  I didn’t steal it, but it was less than shipping the faulty one out for an overhaul.   Next to ordering a replacement, an absurdly expensive option, it was the fastest path I could find to get back up and running again.  After a straight replacement and rough timing by ear, the old cow is purring nicely again and is no longer limited to a two-mile cruising range.   [smiley=clap.gif]

And now I have a spare to work on when I have time.  

So great to be back on the road :exclamation :exclamation :exclamation, but of course, today it rains.    It''s like being back in the UK!

Thanks to all for the advice!

John M