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Ken in Oklahoma wrote:

chasbmw wrote: Ken, if your bike had a digital electronic ignition, then you should fit 5K ohm resistance or there is a chance that your electronics might get blown. Being nice to neighbors is a good thing so I would fit 1K OMH caps on a points equipped bike.

I'm not sure I understand what you're saying. What I'm trying to say is that an airhead will run just fine with 0K, 1K, or 5K resistance whether wires, caps or plugs. Personally I want to be kind to my neighbors so I run with 5K resistance. But I don't have a digital electronic ignition nor does any stock ignition airhead. Am I missing something?

I can imagine that if I were to install a digital electronic ignition, the design might require me to fit 1K caps. And I presume that the instructions that came with the ignition would point that out. Is that your point, reminding me (and others) that some aftermarket ignitions are different? I'm not trying to be cute here. Just to understand the concern.

Ken

Aftermarket electronic ignitions are usually analogue (Dyna, Boyer Mk 111) or digital (Boyer Microdigital, Sachse, Silent Hektik). The digital ignitions require 5K OHM suppression so that any interference from the spark plugs don't fry the processors. The analogue ignitions get away with 1K.

Ken
Newer airheads-post 81-came from the fatherland with stock, factory installed electronic ignition and Hall Effect triggers.These triggers can be blown, I am told, by not using 5K ohm plug caps or by pulling plug wires while engine is running. I do not want to test this statement. It costs money to replace a blown trigger.

BobW wrote:Ken
Newer airheads-post 81-came from the fatherland with stock, factory installed electronic ignition and Hall Effect triggers.These triggers can be blown, I am told, by not using 5K ohm plug caps or by pulling plug wires while engine is running. I do not want to test this statement. It costs money to replace a blown trigger.

Interesting. I have a couple such bikes and I wasn't aware of that. Is the 5K requirement mentioned in the service manuals such as BMW, Clymers, etc. and I just never happened on it?

Plus, conceivably, a person could have done all he could do and installed the 5K caps on his own bike, and then have some other car/truck/motorcycle which doesn't have the caps pull up alongside him at a stop light and then screw up his own bike.

We are talking about EMI (Electro Magnetic Interference (of which RFI Radio Frequency Interference is a subset) aren't we?

Pardon my stubborness on this point. I'm really wanting to make sense of what is being said.


Ken

The stock caps on electronic ignition bikes were 5000 ohms which reduces RFI but it has another impact which is on the duration of the spark. The electronic ignitions will have had a higher spark current than the points bikes and therefore there would be some scope to lengthen spark duration which is a good thing in ignition terms. As well as RFI being a nuisance to others it allegedly could also damage the Hall effect sensor. Whether it was spark duration or better RFI suppression that was the reason for choosing 5000 ohms over the pervious 1000ohm caps I don’t know.

Points bikes seem reasonably happy with either 1000 ohm or 5000 ohm caps although there will be a slight loss of spark energy. It's simple ohms law.

There would be slightly more spark energy on an electronic ignition bike if 100O ohm caps were used instead of 5000 ohms but it hardly seems worth the risk and in any case compared to a points bike it will have spark energy to spare.

Ken in Oklahoma wrote:Interesting. I have a couple such bikes and I wasn't aware of that. Is the 5K requirement mentioned in the service manuals such as BMW, Clymers, etc. and I just never happened on it?

Plus, conceivably, a person could have done all he could do and installed the 5K caps on his own bike, and then have some other car/truck/motorcycle which doesn't have the caps pull up alongside him at a stop light and then screw up his own bike.

We are talking about EMI (Electro Magnetic Interference (of which RFI Radio Frequency Interference is a subset) aren't we?

Pardon my stubborness on this point. I'm really wanting to make sense of what is being said.

Addendum:
I've been away looking on the internet for more information regarding electronic ignition susceptibility to Electro Magnetic Interference. What makes this subject kind of interesting to me is that in my working life I worked for a major supplier of electronic equipment primarily to to the military. I hired on as an EE and eventually became a Program Manager before leaving. As you might expect the military has stringent requirements for its equipment. Among the things we had to test for were radiated and conducted interference and susceptibility. Radiated meant, essentially, through the air and conducted meant, essentially, through the interconnecting wiring. Obviously in an airplane or other military vehicle you don't want to interfere with or be interfered with other systems--unless you're doing it on purpose, such as jamming a radar or communications, or even burning out the enemy's electronic equipment.

With that in mind the notion that it would be OK to design a system that is susceptible to anticipated external emissions is incredible (meant in the literal sense of the word). Now it would make sense to me that if you're building a whole system (such as an airhead motorcycle) then it's OK to modify one part of the system such that it doesn't threaten a different system. Or in the present discussion specifying that a 5K ohm resistance in the ignition system so that the ignition isn't harmed would make sense.

However, to design an ignition system that could be harmed by spurious EMI in the environment just doesn't make sense. I'm not saying that what has been said to me is wrong. I'm just trying to grasp how it could be right.


Ken

Surely it would be conducted interference they were concerned about as the primary side of the ignition circuit is mostly shielded behind metal structures where as the secondary side HT conductors are open to the air.

barryh wrote:Surely it would be conducted interference they were concerned about as the primary side of the ignition circuit is mostly shielded behind metal structures where as the secondary side HT conductors are open to the air.

Yeah. Surely so. The remaining "niggle" would be that the "low" side of the coil secondary is directly tied to the low side of the primary within in the coil, and thence both to chassis ground. The high sides of the secondary and primary are not tied together electrically, but the high sides of both are magnetically coupled (by degrees) within the coil itself via mutual inductance. And therefore what affects one side could affect the other. And I can imagine that could be enough to require a resistor.

In any event thank you all for your ideas.

Ken

I may have missed it, has anyone suggested checking the coils? Coils do age and of course a carbon track or crack in the coils will cause them to fail completely. And of course these are two 6v coils wired in series. You can test the coils by checking their internal resistance with the coils completely disconnected (take pictures before undoing the wires).

Also with respect to books, as you had the heads off, a must is Oak Okleshen's top end handbook. Oak can be reached at askoak@aol.com. I've been wrenching for 40+ years and Oak's handbook is invaluable. While BMW boxer engines are straight-forward, they are devililishly clever the way they are assembled.

You also mentioned the transmission. There is a great website, cycleworks.net. Dan has a DVD on rebuilding the transmission that is excellent. There are some great guys around the US who can rebuild transmissions, notably http://www.largiader.com. Rebuilding the transmissions is tricky and expensive. The video can give you a sense if you want to take on a project like this. There are a couple of tools that are absolutely required. An alternative is to find a used transmission on eBay.

With respect to your not being acquainted with carbs or points, you remind me of my 26 year old son. He is an expert mechanic and calls me when he or his buddies need help with carbs or points. It's great frun to be useful to these young and extremely clever young guys who do amazing things and know how to tune and mod their cars and bikes with chips and computers!

The R90 is a great bike. Hang in there, it's worth the effort.

Dave
1975 R90S
2000 R1100RT