Pagoda SL Group

W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: jcochran@cox.net on July 16, 2014, 00:34:52

Title: Spark Plug Gap
Post by: jcochran@cox.net on July 16, 2014, 00:34:52

Hi,
 Does anyone have a recommended plug gap for BOSCH #WR 7 DC+ (7900) sparkplugs that I am installing in my 1967 250SL?

Thanks for your help,
Jim

Title: Re: Spark Plug Gap
Post by: 66andBlue on July 16, 2014, 01:29:54

Jim,
are you aware that you are using spark plugs with a resistor: WR 7 DC+ (7900) ?
Joe A. wrote up a good post why they should be avoided in our cars: http://www.sl113.org/forums/index.php?topic=7922.0 Reply #10 and others

Title: Re: Spark Plug Gap
Post by: badali on July 16, 2014, 01:50:09

I use w7dc (7500) and set them at .035.  The car runs fine for me.  My main problem is keeping the points at a proper gap for good running.

Title: Re: Spark Plug Gap
Post by: jcochran@cox.net on July 16, 2014, 02:26:48

Thanks to you both for your help. I recently had my Pagoda restored and I am having issues with it missing no matter what the A/F ratio is. I just ordered a set of W7DC's from Rock Auto and hopefully they will do the trick - it's certainly worth a try.

Thanks,
Jim

Title: Re: Spark Plug Gap
Post by: 66andBlue on July 16, 2014, 02:36:00

While you are at it also check your spark plug wires.
I had a misfiring problem on my 230SL and was fortunate that I looked in the engine bay when it was dark.
Sparks along the #1 wire!!  :o
Also use an Ohm meter to check resistance values from end to end on each wire, should not exceed about 2 K Ohm.

Title: Re: Spark Plug Gap
Post by: ctaylor738 on July 16, 2014, 12:32:00

According to the technical manual, total resistance (from the coil through the spark plugs) should be between 13k and 16k ohms.  I believe you will find 5K in the rotor, and 5K in the WR plugs, so you can "afford" another 5K in the wires. 

Cheers,

Title: Re: Spark Plug Gap
Post by: ja17 on July 16, 2014, 14:40:37

Add more resistance for the spark plug ends and the distributor plug ends and you are getting close especially if you are using 5K resistor spark plug ends. Avoid the resistor plugs if you can.