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Spark Plug Wires

This is about a half hour job once the tank is off, and is a good learning process, or at least it was for me. My spark plug caps weren't seating properly on the plugs and I figured the little insert that grabs the plugs were either shot or missing in action. Neither turned out to be the case. Once I dissected them, they did work. A little late wouldn't you say ? After looking at the old caps, I got the feeling that I couldn't get the caps to seat properly for a couple of reasons. Two of them were quite tight, and with so little room to get your hands in to really push down, friction won the day. Additionally, it seems that the rubber was just compressing under the force. The new caps are hard plastic and don't compress.

Here's a replacement cap from NGK

  • S is for straight
  • D is for 10 & 12 mm size plugs - Concours size
  • 05 is for 5K ohms resistance
  • F is for terminal stud
  • P rubber cap (optional)

SD05F is the one you want. All my dealer could get was the SD05FP. Not sure which rubber cap they meant but they both stayed on so I don't know which one is missing on the SD05F. 

Dennis Kirk had these listed in the 2003 catalog
for $3.30 each

Take off the wide rubber boot off the top of your old caps and reuse them

The picture is a bit fuzzy but you can see the little screw in the center. This screws into the plug wires.


This is the OEM version disassembled. The main body of the cap is a one piece unit. The replacement NGK part is 3 parts. The body and 2 rubber boots. The large boot on the left is what keeps the rain, dirt and stray road kill out of the spark plug wells in the cylinder head.
The new cap in place with all the rubber boots. There was a trace of dielectric grease on the connections from the factory. Before you screw it back together, put a little on all connections.
These are the old caps dissected. The brass insert is the thing that grabs the tip of the spark plug with that nice ratcheting sound as it sinks into place.

If you plan to replace the wire ( I didn't this time around ), you will want to remove the cap and the ring from the coil end of the wire. With a little silicone spray shot down between the cover and old wire, the wire cover is removable and can be put on your new wires if you choose.

Article By: David J. Morrow

Updated January 2005

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