Spark plug lead falls off.

[klaviator]

Some time back my Aprilia wouldn't start.  The spark plug lead had fallen off the plug.  Since I had recently replaced the plug I assumed I hadn't put it on right.  The it happened again.  I put it back on.  Then no problems for a while until last night when I rode it to bike night.  Stopped for gas and the engine died.  Put the lead back on and rode to CG for bike night.  On the way home the motor started dying.  When I stopped and put the lead back on it didn't have any tension holding it on.  I used a zip tie to position the wire to the lead to keep it on.  This morning I took a closer look.  I have never had this sort of problem before on a bike or car.  After fiddling for a while I discovered the lead screws off of the wire.  Is this normal?  Can I just replace the part that attaches to the plug?  Should i get the Aprilia part or is this a common part that is interchangeable?

This is the wire leading to the lead:



Spark plug lead and spark plug.



I'd rather not have to replace the entire wire and lead because removing the bodywork to do that will be a PITA

[Bluesman]

looks like you should be able to replace that part since it disconnects.My  H/D wires are one piece so I am not sure.I would call the dealer.

[Brian A]

Yes. On those style wires the cap does thread directly onto the plug wire. If you haven't already done so, shine a light down into the cap and you can see the "screw" that threads into the center conductor of the plug wire.
You can try making a clean cut on the plug wire 1/2 inch or so back and thread the cap into fresh wire.

[klaviator]

The connection from the lead to the wire was fine.  The problem was that the lead had a real loose fit on the end of the plug.  I think I'll swing by Midway Cycles tomorrow and see if they might have a lead that will work. 

[Brian A]

The connection from the lead to the wire was fine.  The problem was that the lead had a real loose fit on the end of the plug.  I think I'll swing by Midway Cycles tomorrow and see if they might have a lead that will work.

OK. I undermistood.

If you have no luck, let me know. I think I have a few of those caps. I'd be happy to send you two (assuming I do have them)

[klaviator]

Thanks.  I think I should be able to find something that will work around here.  I just never new that those caps were replaceable.  I thought I might have to replace the whole assembly.  I just happened to notice that the cap could be unscrewed from the wire. 

Another 40 or 50 years of messing around with this mechanical stuff and I might become a semi competent mechanic. ???

[klaviator]

I stopped by Midway Cycles.  The cap I needed is an NGK part and they had it in stock for $4.95.  I wish all my mechanical problems were this easy and cheap to fix :)

[Argh Oh]

Wow. $4.95 to fix an Aprilia. You are a lucky man, glad it worked out! It costs more than that to put air in my tires.

[klaviator]

Wow. $4.95 to fix an Aprilia. You are a lucky man, glad it worked out! It costs more than that to put air in my tires.

You need to stop buying that imported Italian air for your tars. ;)

[GSlater]

I may be showing some of my ignorance here but...
Does that plug end fit to the sparkplug without the cap? (raw male threads)

[klaviator]

I may be showing some of my ignorance here but...
Does that plug end fit to the sparkplug without the cap? (raw male threads)

Actually, my ignorance when I started this thread led to me using some wrong terms.  I should have said "spark plug cap falls off of spark plug."  The cap screws on to (actually in to) the ignition wire which I believe is also called the lead.  The cap is just pushed onto the plug end and is held there by friction.  What happened to me was that the inside of the cap, and possibly the plug end also, had worn off enough that it didnt fit tight enough to create any friction. 

There is no way to connect the lead directly to the spark plug without the cap.

[Argh Oh]

You need to stop buying that imported Italian air for your tars. ;)
[/quote]

It's very special air.

[Mulley]

When changing my plugs on my Aprilia Tuono I pulled the guts out of the cap. It just wouldn't let go of the spark plug. So the metal clips separated from the rubber boot.

Aprilia wanted a small fortune for the exact part number which was made by NGK just for them. I found a suitable NGK equivalent that was just a little shorter but worked exactly the same and only cost a few bucks.