I have read on other forums people finding after market ignition wires and caps.
This could be a big money saver, but..... (yes there is always a but)

The K100 is originally fitted with Bosch X5DC (or NGK D7EA) which is a non resistor spark plug. Here is the reason:
The spark plug cap already integrates a resistance of 5KΩ. Similarly, the connector at the other end of the ignition cable also includes a resistance of 1KΩ. The total resistance is 6KΩ
If you replace the wire with an after market non resistor wire and cap and keep the original spark plugs, you will run into troubles and take a chance to blowup the output transistors of the ignition module(You won't have any resistance at all).
It is possible to fit a K100 with after market plugs and wires, but the spark plugs have to be replaced with a resistive type (Bosch XR5DC). The XR5DC have a built in 5kΩ resistor.

What the number in the model # means?
The X(R)5DC has a thermal index of 5 the NGK D7EA has a thermal index of 7 but both are suited to be installed on a K100 engine....
Confusing? Well each manufacturer uses its own designation for the heat range:
On the Bosch plugs the higher the number (from 4 to 8 ) the hotter is the plug. NGK works on the opposite and goes form 8 to 4 (a lower number indicates a hotter plug)

The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine head. It has been found the optimum combustion chamber temperature for gasoline engines is between 500°C–850°C. When it is within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits which cause fouling.

The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges. When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter.

Hope this information will be beneficial to you.

Bert

Hi Bert, Your write-up is very interesting. I've been thinking of replacing the K75's ignition leads for some time. In my opinion.. twenty plus years is enough for any HT lead.

I've bought connectors for the coil end of each lead, they came from a local VW parts specialist. I still need to get the cable and plug caps. My plan is to use copper wire plus NGK resistive plug caps. The joint at each end of the cable will be sealed flexible epoxy.

Do you have comments on the plan.

Malcolm
Joburg
South Africa

Hi Malcolm,
I don't have one but recall mention that the K75 has a spark gap built into the plug cap which is why they read open circuit when you test them with a meter.
Regards,
K-BIKE

Or is that when people fit spark plugs without the little bobbins fitted? I would be interested to read about that, as it doesn't seem to make sense (to me that is!!).

Hi Rene,
Did a bit of research and the K75 has a spark gap built into each plug lead hence they are always seen as open circuit if one tries to test end to end.
Regards,
K-BIKE

The spark gap on a K75 is very interesting, I checked mine at weekend wondered why the resistance was all over the place.

It sorta sounds like thee is little option but to pay BM's huge price for new leads, some extra reasearch is inline here.
I'll get cracking

Hi,
I suggest you try http://www.motoelekt.com/new.htm
Nice to deal with and they ship.
Regards,
K-BIKE

The link is very interesting. I see they use NGK plug caps, I wonder if the include the K5 spark gap ??

malcolmt wrote:The link is very interesting. I see they use NGK plug caps, I wonder if the include the K5 spark gap ??

Here is the description from the site:
"These spark plug wires are made from very good quality jacketed copper cable, with the correct 5K ohm resistor in the NGK caps

If you look down a little further on the description they say "We have to get the K75 ends from BMW, which is why the 3 wire sets have to sell for the same as a 4 cylinder set. By using the exact correct part, easy fit and long service are assured."
Regards,
K-BIKE

I presume the K75 end is the coil. I bought plug from a VW specialist which apear identical to plug on my original cables.
I wonder if the spark gap is in the coil or plug end???

I noticed the plug caps from motoelekt are angled at what looks like about 45 degrees, the stock are 90. Won't this interfere with the plug cover plate?

The NGK caps I bought are angled at 102deg, there is sufficient room for the leads. I'll put mine together once I've solved the spark gap problem.

Has anyone dicected a U/S lead and may know how big the gap is ??
Malcolm(t)

Just for information, here is a picture of the built in resistor in the spark plug cap. The ceramic has been broken to expose the resistance.

Gentlemen - first before anything

I am NOT an expert [ or anything near ] on electrical things.

However, when we wanted to look at replacement leads for the K100 / K1100 we contacted an ignition manufacturer [ UK ] who supplies amongst others - Aston Martin, TVR, Jaguar, Audi, BMW [cars] and MANY racing and competition applications - also the leads for our Race Cobras and C Type Jaguar replicas. He has been in business for 20+ years. They have FULL laboratory facilities for testing and manufacture the components in their own factory.

I sent them OEM leads and coils for K100 and K1100 - after laboratory testing they have now manufactured suitable leads which are on the market. Due to the large number of K75 enquiries we got, I sent him K75 leads, coils etc. for analysis and replication. This is nearly completed now.

However, not knowing any better when I saw the various forum [ ALL forums ! ] arguments about the K75 "air gap" I sent the queries to him. What follows is his copied and pasted response in it's entireity.
Dear Manfred,

Thank you for your e-mail.

Be assured, there is no 'air gap'. The leads on the bikes use the same technology as the BMW cars, as do VW, AUDI, etc. etc. because most of the lead sets are made by Beru.

The cable is copper cored and the boots have an internal 1kOhm resistor at the coil end and 5kOhm resistor. The resistor is made from a compressed carbon material. As I said before, identical to the car manufacturers. People may believe the resistor to be an 'air gap', but it isn't. It is there to suppress the EMP pulse (interference) by restricting the electrical flow.

This 'air gap' myth is donkeys years old. People use to attach a 'button' on old copper core cables to make the spark 'jump' across the gap. The theory is that the air gap acts like a capacitor and 'compresses' the spark, therefore making the spark burn duration shorter and more energy released in a shorter time at the sparkplug. I am sure in a laboratory and you are running at 10,000rpm it may have some slight effect on engine timing, but in the real world it is nonsense.

Hope this helps!

There we have it gentlemen - from the man who manufactures ignition components for a living.

I personally will not join in this debate as I am not qualified.

Knowing Beachcomber (Manfred?) to be a very modest man...he IS an expert and you can order leads through him and get a discount as forum members.
He has been in the "Game" for many years and is well known in the racing world and engine development. He knows yer know....despite his modesty.
Ajays.
He who knows and knows not he knows is a fool shun him.
He who knows and knows he knows follow him. the Bard.

Wow - Ajays, was that Brandy or Whisky I should send?

Those that know me well - business colleagues and friends alike - will understand that I do NOTHING without 100% research and thorough testing.

I am an engineering graduate and spent my early working days designing some very interesting projects. However, even after 45 years of being involved with racing/speciality/replica cars, both design and manufacture - I AM STILL LEARNING.
If I am not completely qualified in a topic [ like electrics] I will find people who are.

Manfred - AKA Beachcomber, TJ

I have seen a lot of K75 owners with running bikes who have noted their leads show infinite or open circuit resistance, I suspect the comment made by the lead manufacturer with regard to K75's is incorrect either that or all the others are wrong.
Regards,
K-BIKE

Hi K-Bike,

Like I said - I know nothing.

However I have passed your comment on to the lead / ignition components manufacurer for his comment. BTW- all "the others" - they live in the World of ignition component manufacture as well [ 20 + years] ?

Here some useful information related to spark plugs from NGK. It simply explains the differences and intended uses in plain language.

BTW the NGK plugs for K100s is D7EA as you know and a resistor type is DR7EA. If anyone is interested, I have a pdf which gives tech details for all the NGK plugs.

http://docs.google.com/fileview?id=0B7_6gDPDREzKNTQ4MWI2YmEtMDAzMi00MzA3LWEwMDMtZTU4MzQ1ZmU5NzQz&hl=en

Does beachcomber(manfred) still sell plug wire sets? Any idea how much they are?

Well, nothings been mentioned in the last 8 years, but if you have a look here, your questions will be answered. Realm Engineering is the mob who make the leads, based in the UK.


I use them...great leads and no problems.