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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: CTDOM! on May 02, 2021, 10:06:55 PM

Title: Spark plugs W5DC or XR7LDC
Post by: CTDOM! on May 02, 2021, 10:06:55 PM

Hi all,

Figured it was time to check plugs on the 92 K1100RS.  I had ordered a set of XR7LDC's since this is what BMW recommends.  Well the plugs I took out were NGK's and the top nut was not installed, it was just the threaded rod.  The XR7LDC's don't let me screw them off.  I stalled the new plugs but the boots don't seem to go on as far as the old ones.  Bike runs nice with them.  I cleaned out the inside of the boots, heavy grey corrosion in there.

So are they supposed to have the bare threaded rod or does anyone have any experience with the XR7LDC's?  Thanks!

Title: Re: Spark plugs W5DC or XR7LDC
Post by: The Mighty Gryphon on May 02, 2021, 10:32:14 PM

For the best performance, the plugs should have the terminal nuts installed when using the OEM spark plug cables.  The bike will run without them, but other owners have noted misfiring problems.  In my experience, most aftermarket plug wires now work with the threaded stud without the terminal nut.

Some plugs have the nut permanently installed, while NGK provides plugs with a removable nut.  A call to NGK USA tech service will get them to send you terminal nuts at no charge.  You can also get them by going to any small engine repair shop.  They often have old plugs that the nut can be removed from and used on your NGK's.

It's a bit of an inconvenience to have to save the terminal nuts off my old NGK plugs, but I don't mind because they offer excellent performance at a very reasonable price.

Title: Re: Spark plugs W5DC or XR7LDC
Post by: CTDOM! on May 03, 2021, 06:34:32 AM

I appreciate the response.  The NGK's I was replacing were bare thread but the new XR7LDC's that I am replacing them with have the nuts.  The new Bosch plugs are installed and it seems to be running fine.  Thanks!

Title: Re: Spark plugs W5DC or XR7LDC
Post by: frankenduck on May 03, 2021, 08:43:19 AM

Running the plugs with bare threaded tips is a great way to make the spark plug spark at both ends. :johnny

Title: Re: Spark plugs W5DC or XR7LDC
Post by: CTDOM! on May 03, 2021, 09:33:02 AM

Frankenduck- That is probably why there was so much grey gunk which came out of the boots.  I cleaned the inside with contact cleaner. 

I was mostly paranoid that the boots would slip off as it seems they didn't engage the plug as far in.  I will give it a whirl.

Finishing up the final drive big bearing replacement due to play in the rear wheel and I can give it a proper test run.

Thanks all!