Aftermarket ICU

[Strapnug]

Hello--First post. Had old "gray" coil with cracks and open secondary on my newly acquired 83 R-65. Replaced coil with upgrade Bosch with .5 ohm primary. I understand that I need a late ICU to handle the new style coils higher current. Anyone have a good upgrade Bosch-284 Icu for sale or any experience with using the EnDuralast R284 aftermarket replacement Module?--Regards JBP in Wichita

[georgesgiralt]

Hello !
In 2012 I put my R65 (bought new in '84 but made in '82) back to use. I replaced the cracked coil by the new Bosch design.
I did not change the ICU then, and the bike is still fine, more than 20 000 km later. So save your bucks for something else (new tires or gas ...)

[Barry]

The 0.5 ohm coil you have was only introduced in the early 90's and needs an ICU with electronic dwell control to function reliably. If you can find the ICU part no for an early 90's bike  that will do the job.

Your existing ICU is only good for a 1.5 ohm dual output coil.

[georgesgiralt]

Yes Barry, it is what it should be. But my old ICU runs perfect on a new coil. seems the dwell was already controlled at that time.

[Barry]

Yes Barry, it is what it should be. But my old ICU runs perfect on a new coil. seems the dwell was already controlled at that time.  

Are you sure you have a 0.5 ohm coil on an old ICU ?

I would check it Ignition on with an ammeter in series. If the coil is 0.5 ohms it should pull 24 amps....  but not for long. Either the ICU dwell control will shut the current off automatically after a few seconds or the coil will overheat and burn out.

It might be that the early ICU's have the crude type of dwell control that protects the coil from the above "ignition on but not started senario" but doesn't have the sophisticated type of dwell control that works while the engine is running to limit coil charge time at low revs. You should get an indication of that by monitoring the average running current at low revs.  If it's still relatively high say 12 amps or more then there is no running dwell control and if that's the case it results in a very inefficient ignition system in terms of the load it puts on your battery and charging system. For that reason alone I would never consider using a 0.5 Ohm coil without the correct ICU.

[Bob_Roller]

Here's Snowbum's discussion of the ICU's and coils, you need to scroll down the page a ways to get to it .

http://bmwmotorcycletech.info/Ignition.htm

[Barry]

Here's Snowbum's discussion of the ICU's and coils, you need to scroll down the page a ways to get to it .

http://bmwmotorcycletech.info/Ignition.htm

Just read through that very quickly and both Snowbum and Oak confirm that the 0.5 or 0.7 ohm ohm coils used from 91 onwards should only be used with the correct latest type of ICU which has a turquoise paint dot.

If had to pick the most sensible combination of of ICU and coil it would be a 1.5 ohm coil with the latest ICU that only passes current when engine rotation is sensed.

[georgesgiralt]

Barry,
I've checked that my coil is 0.5 Ohm. And my ICU has a P/N ending in 113 (I can't easily read the other part, but it is the one fitted on the new bike in 1982 which has a kick starter).
I've bough (for a friend far away) a brand new and current ICU at the BMW dealership. Before sending it I ran the bike a couple of days with it and noted no difference at all.
I can't exactly tell what's inside my ICU and how it works exactly, but the bike runs fine in every respect.
I bought my coil in 2012 from a respected local airhead Guru it came in a BMW box with the latest P/N on it. I still have the invoice and the box, so I can give them if need be. He did not told me I had to change the ICU and he routinely change the "crack-o-matic" coils for the modern version without, as far as I know, any complaint from it's customers.
Last but not least, in France (and in Europe) these ICU where fitted on a lot of cars of that era. I know a lot of airhead owner having replaced a failed ICU by one found at a car wreck and from cars as different as Audi or Peugeot 104 ! and are satisfied with it.

Maybe my setup is far from prefect but it runs fine since 2012 and has "suffered" around 15 000 km. It is not based on theory or design analysis but on personal experience. So maybe the OP can save a few bucks if he is as lucky as I am ....

P.S. : If you enter the BOSCH P/N of the ICU into a car part shop database, you get a very long list of car using this particular P/N and also a very long list of compatible P/N from BOSCH or different makers. It seems this ICU has had many makers and a lot of modifications all sharing a "common" design or compatible wiring. (I've tried the French Oscaro.com supplier)

I do hope this will help.

[montmil]

My 1986 VW Cabriolet has the same ICU as my R65s. And the distributor has a Hall sensor just like...

[georgesgiralt]

Hello Guys,
Searching for a leak on the bike, I hooked an ammeter so I'm able to say that :
Using the old (31 years) ICU made for a kick starter and the latest Bosch coil with the very low primary resistance I have the following figures :
Contact ON engine not running : 8.11 A
A few seconds after, still contact ON and engine not running 0.8 A.
So I can infer that the coils are fed with around 7.3 A by the ICU !
So I can tell that my ICU is apt to drive the 0.5 Ohm coil without burning out...
If that may help out save some bucks...

[Barry]

That's good data Georges.  

I think the drop to 0.8A is just the basic dwell control that shuts the current off if the bike doesn't start after a few seconds.  

As for why the 0.5 ohm coil only pulls 8 amps I guess if you consider the fractional amounts of resistance in all of the wiring from battery to ignition switch to kill switch, back to the coil  and then the ICU transistor itself will have some resistance (if it didn't they wouldn't get hot). There is also the internal resistance of your ammeter.

Add all that lot up and it probably exceeds the 0.5 ohm resitance of the coil and helps to keep the current down.  The way to check would be to measure the volt drop across the coil with the  8 amps  flowing. I suspect it will be less than 12 volts.  

Another possibility is the ICU is smarter than we think.  Modern ICU's certainly have current limiting capability built in.

[nhmaf]

And your voltmeter/multimeter can't display the "peak" current waveform that may be alot higher than 8A but for a brief moment of time

[georgesgiralt]

Well as the 8A figure last for a few seconds, I think the coils are fully charged and that the magnetic circuit is saturated...  
These ICU are clever than we thought. I remember having opened a fried one years ago and found a couple of integrated circuits inside. So definitely more complex than a simple transistorized circuit.

[Barry]

Who knows exactly what Georges ICU's is doing but just to clarify the way ignition coils behave.

When a coil reaches saturation it carries on pulling maximum current which is dissipated as wasted heat hence my comment early in this thread that a high current ignition system without dwell control is potentially very wasteful at low revs. This is the very reason why modern electronic ignitions introduced dwell control to limit or cut off the current on every cycle once the coil reaches saturation. Without dwell control the low resistance coils employed in these ignition systems would overheat.

This is also why I was concerned about using 0.5 ohm coils on an ICU that might not have had had sufficient dwell control. Georges experiment has shown that it shuts the current off after a few seconds to protect the coil but that's not because the coil just got saturated. The coil will have been saturated after the first 5 milliseconds.  That the ICU or system resistance limits the current to 8 amps means it probably doesn't matter if the ICU is of the modern smart enough type that will shut the current off every cycle once the coil is saturated i.e. after 5 milliseconds.  Had the coil pulled the nominal 24 amps that it's 0.5 ohm resistance implied then the sophisticated type of dwell control that works every cycle would have been absolutely essential.

[georgesgiralt]

Yes, Barry ! It is exactly what I'm saying. My old ICU, despite what is said by others, can perfectly control coils with 0.5 Ohm resistance in the primary.
Statically, it limits the current to around 8 A, then it prevent overheating by cutting off the current after a few seconds without engine starting. And during normal use it manage the dwell well enough for the bike to have run around 15 000 km without a glitch.
IMHO, the newer ICU model are, maybe, better in controlling the dwell but this has still to be proven. Why ? Because the very same unit I use was used into cars with low primary resistance in their coils.
As I do not work for Bosch nor BMW I can't prove my saying except by trial and error....
At 178 € for a new ICU from BMW, I prefer to try using my old one