'93 K1100LT Spark Plugs

Hello all,

I'm doing winter maintenance on my '93 K1100LT and I have a question about spark plugs. Last summer I bought seven Bosch X5DC spark plugs, three for my K75 and four for the K1100. Unfortunately, I now see the correct plugs for the K1100 is XR5DC. I understand the "R" means it is a resistor plugs.

My question is, can I use the X5DC plugs or should I buy XR5DC plugs?

Thanks for your help.

Regards,

Richard in Commerce MI.

I don't know "for sure", but the MAX site shows the correct plug for a '93 K1100 to be the XR7LDC.
EuromotoElectrics says this plug is no longer available, and infers that the XR5DC (slightly hotter) is the replacement.
The BMWLT.com site shows the NGK DCPR7EIX as a replacement;
The NGK DCPR7EA9 may also be a replacement.
You may or may not need to save the nipple nuts from the older plugs.

About the "R" part of the designation - If the bike has "resistor"-type spark plug wires, one doesn't typically use resistor plugs also, they don't play well together; but if the wires are non-resistor types, then if the manufacturer installed resistor plugs, that indicates the ignition system expects to see that in the circuit.

see also:
https://forums.bmwmoa.org/showthread.php?3705-XR7LDC-What-is-this-spark-plug
https://forums.bmwmoa.org/showthread.php?18266-the-right-spark-plug-for-a-1992-k100rs

Hello Paul,

Thank you for the information. Both the Owners and Factory Repair manuals list the XR5DC as the proper spark plug. The bike has factory wires, so if the bike came with resistor plugs, then I wouldn't think they are resistor wires.

I'm going to purchase DPR7EA-9 plugs for the bike.


Regards,


Richard
Commerce Township, MI

Usually the resistor part would be in the spark plug head. You can see if you have resistor wires by using an ohmeter to measure the resistance from one end of the plug wire to the other. Don't know what resistance to expect...on mid 70s-on Airheads, the plug head had a 5K ohm resistance.

Hello,

I looked at the wires last night and the heads are marked 5K ohms.


Regards

Resistor plugs might work but there's a chance that they would misfire or the engine would run rough. No need to add extra resistance to the spark path.

An aside for any K75 guys that are reading this thread: K75 (not K100 and not aftermarket) wires will read OPEN (no continuity) because there is an air gap in the end of the wire. For that reason, you don’t want to run a resistor plug on a K75 with stock wires.

Now back to our regular programing.

Excellent point, Lee!

And speaking of plugs, plug connectors, and plug wires - Looking at the parts fiche over the various years, with specific attention to the '93 K1100, there is shown a "suppressing socket" on the coil end of the wires. I spotted only one photo where an omega (Ω the symbol for resistance) was actually visible, and that was on the plug cap itself; no actual resistance numbers were visible or specified.

Bottom line - measure what you've actually got, and if they're "resistance" wires (w/ connectors), and if resistor plugs seem to cause rough running, you know what to do about it.

Follow up,

So I purchased DPR7EA-9 plugs and installed them on Monday Feb 13th. The Bosch plugs that i removed take a (if I remember correctly) 17mm socket, the NGK plugs not so much. They need an 18 mm socket, so a trip to NAPA was in order. I should have bought Bosch plugs. I'm not sure if the oem tool kit has an 18 mm socket.

Regards,

Richard in Commerce MI