The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: steve_wicks on February 18, 2009, 12:03:20 PM
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I discovered my bike is fitted with two car type coils. Local airhead specialist says it'll burn out ign stuff on front of engine, but is he just tryoing to get me to buy new coils at about $280 ? I've got no idea how long they have been on the bike, but judging by the ht leads I reckon its been a long, long time.
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The crystal ball works better if you supply year, etc...
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Sorry ..... oops. Maybe I should have read my Haynes manual before I fired off that post. The coils look like non electronic coils.
My bike turns out to be an '81 model although registration documents etc say it was first registered in 1984. Just the straight forward R65.
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Hmmm, '81 should be electronic but I suppose a very early one might not be? The thing is, you can practically use whatever coils you want as long as the primary resistance is correct. The pre-electronic ignition bikes used a pair of 6v coils that were commonly used on Volkswagens...
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My brothers 81 r65 has the same 6v coils as mine (80 r65) yet loads of other differances brake master cylinder wireing ect but points on the ignition not electronic??/.carbs are differant ect.
Lou
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I haven't figured out how to post a link to a specific thread in boxerworks forum, but a knowledgeable fellow by the name of Stephen Bottcher (who is affiliated with Omega) wrote the following - I think that he has researched this pretty well:
<How important is it to match the coil to the ICU?>
VERY.
<if a coil from a 1990 R100RS is used in a 1982 R100RS, should the ICU also be changed?>
NO but it depends whether a kickstarter is installed
<Must these also be matched to the correct coils or are they a plug and go substitute?>
YES, they must be matched.
It is more complicated that I care to admit (the long form is here on the bottom of this page: http://www.stephenbottcher.net/~omega/faq.html):
The ICU (I call them A or B below) is rated for a certain coil resistance. With a given coil, you can use any coil/-combination that has a higher resistance than the one it is rated for, see below:
1969-1980 (points): 2 x 6V coils, 2.4Ohm, works with ICU A, B
1981-1984 (ICU A): 2 x 6V coils, 1.2Ohm, works with ICU B
1985-1993 (ICU A): 12V dualcoil, 1.2Ohm (gray HT posts), works with ICU B
1993-1996 (ICU B): 12V dualcoil, 0.6Ohm (red HT posts)
There is a third variable: there were ICU's with a 1.5sec cut-off time (no kickstarter) and a version with 5sec (with kickstarter). I don't know exactly where and how that fits in. It isn't relevant for the Coil-ICU relationship, that I know.
Hope that helps more than it confuses, Steve. I can't explain it any simpler, it is already highly simplified. My professor would give me an F for it!
Basically, you can use a coil with an ICU as long as the coil has the SAME OR HIGHER primary resistance (OHMs) as the coil the ICU was originally designed for.
If you use a coil with lower resistance than the ICU is intended for it can cause overheating or eventual burnout of the ICU.
If your bike is an 81, then any 6V coil that is at least 1.2 Ohms primary resistance or above should be fine, or you can use the Dyna Brown dual coil (1.5 Ohms) which takes a lot less space. If you were to try to put in a 0.6 ohm new coil from a 93-95 airhead, you'll shorten the life of your ICU.
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I fitted a pair of (non-identical) car coils to an 1981 R65 in an emergency and the ecu burned out about 2,000 miles later. May or may not be a causal link as I was sometimes careless about leaving the ignition turned on.
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Some R65s have dual "car" type coils. Mine does. If your curious 'nuff Ill pull the tank and shoot pics.
rich