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Old 11-30-2012, 09:34 AM   #1
Prmurat OP
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Spark plug cap

I just bought a R80g/s and I hope this second venture in the BMW world will be better than last one (a 90/6 dressed as a /5).
There is something I do not understand with Beemers: everyone seems to idol the stock (Bosh?) white pot metal spark plug caps... Are they not too old by now and need replacing?? Born and raised in Europe I saw these caps on everything from mopeds to big bikes (DOT regulations) and I think they are ugly even when new!
So any reason(s) not to change them (apart of the "jt is stock" wanking!)?
Thanks.
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Old 11-30-2012, 09:37 AM   #2
chasbmw
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I use NGK plug caps, depending on the bike you may need either 1000kohm or 5000kohm resistance in your plug caps.
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Old 11-30-2012, 09:58 AM   #3
Horsehockey
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NGK works for me. It's also pretty well established that the OEM metal caps are subject to shorting in the rain as they age.
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Old 11-30-2012, 10:14 AM   #4
Mark Manley
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Those metal caps caused my first motorbike, a brand new Puch moped to breakdown on my first day out on my 16th birthday, I have hated them ever since, go with NGK.
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Old 11-30-2012, 10:25 AM   #5
disston
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Points ignition gets a 1000 Ohm plug cap. Electronic ignition gets a 5000 Ohm plug cap. That's what I've been told but I run the rubber BMW caps with integral wire that is 5000 Ohms on my '75 R90/6 and have no problems. I don't run the metal plug caps because of the shorting in the rain problem.

So I ordered the NGK plug caps from Ted Porter's Beemer Shop and they sent me 5000 Ohm caps. I guess it's OK.

I forget the reason but we are supposed to do it this way. The resistance in the cap. The plugs are Non-resister. If you want the reason I think Snowbum talks about it on one of his pages. And he being an Electrical Engineer or some kind of a genius will have you convinced this is how it's done. As soon as you finish reading that come back here and explain it to us.
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Old 11-30-2012, 10:36 AM   #6
Horsehockey
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Charlie-
I think I can help: pulling plug caps off while the engine is running will sometimes but not always, fubar your coil(s). And sometimes, but not always, will fubar your electronic ignition (if you have one). The ignition will grenade (a) immediately; or (b) at some indefinite time in the future; or (c) never. Meanwhile, running 1K ohm caps on a 5K ohm bike will sometimes, but not always, cause weak spark which you will sometimes, but not always, notice. Running 5K ohm caps will sometimes, but not always, cause weak spark which you will sometimes, but not always, notice. I hope this clears things up for you.
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Old 11-30-2012, 10:40 AM   #7
disston
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That's the best explanation of plug cap resistance and blowing electronic or none electronic ignition systems I've ever read. Thanks Bill. It's so clear now.

Charlie
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Old 11-30-2012, 10:46 AM   #8
Horsehockey
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Quote:
Originally Posted by disston View Post
That's the best explanation of plug cap resistance and blowing electronic or none electronic ignition systems I've ever read. Thanks Bill. It's so clear now.

Charlie
Glad to help Charlie. After I got my eyes surgically uncrossed after reading Snowbum's articles, I waited about seven years and it all sort of distilled down to this for me.
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Old 11-30-2012, 11:12 AM   #9
craydds
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Quote:
Originally Posted by Prmurat View Post
So any reason(s) not to change them (apart of the "jt is stock" wanking!)?
I like the look of the old bikes and those restored with all original parts. But, I run the NGK plug wires, 5K ohm, on my R90S; just bought a set from Rick Jones at Motorrad Electik. Told him I had the Boyer ignition, he said 5K ohm was for the electronic ignitions.
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Old 11-30-2012, 12:04 PM   #10
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The shields easily come off the Bosch originals if that is your concern. I had one short like that 30 years ago. I have used the same setup since until I just recently dual plugged. No problems. I don't think those shielded caps fail too much more often than most but I guess they do to some degree.
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