Pagoda SL Group

W113 Pagoda SL Group => Electrical and Instruments => Topic started by: hauser on August 13, 2009, 02:04:06

Title: W9DC Spark Plugs
Post by: hauser on August 13, 2009, 02:04:06

Hello Alfred

I have a Crane XR700 installed in my '69.  As you know I take it to Continental Imports in Gainesville for service work.  In my six years of going there the plugs have been replaced twice with W7DC according to the invoice.  However the tech said he had used a WR7DC.  I have upgraded the alternator to a 55amp Bosch unit and every once in a while for a split second the engine will cut off.  All services are up to date.  Could this have anything to do with the spark plugs? 

If my plugs are indeed the W7DC what changes if any would the W9DC plugs make?

I apologise for the inquiry considering this is the items for sale section. :-[

Title: W9DC Spark Plugs
Post by: Benz Dr. on August 13, 2009, 02:30:46

W7DC are the recomended plug for a lot of these older cars but for the most part they're generaly too cold. Unless your engine has perfect compression, doesn't use any oil, and everything is at optimal settings, they often foul out and can make your engine run rich.
The hotter plugs heat up faster and run at a higher temp. This helps to keep them clean so the chance of fouling and then misfire is for the most part reduced or eliminated.

Title: W9DC Spark Plugs
Post by: hauser on August 13, 2009, 03:27:04

What should the gap be on a W9DC?

Title: Re: W9DC Spark Plugs
Post by: jacovdw on August 13, 2009, 09:43:26

The gap should be 0.7 mm or 0.028 inches (if I have my conversion right).

That is assuming that you are running a stock ignition system. With a "modified" ignition system, you can open the plug gap a little.

I'm using NGK BP6ES gapped at 0.9 mm with a Bosch red coil, 1.8 Ohm ballast resistor, 1 kilo Ohm plug ends and a Pertronix ignitor.

Title: Re: W9DC Spark Plugs
Post by: waqas on August 13, 2009, 17:45:48

Don't all these plugs come pre-gapped now?  I've never had to set the plug gap when putting in new plugs.

Title: Re: W9DC Spark Plugs
Post by: graphic66 on August 13, 2009, 18:08:18

A slight bang or bump can change the gap. You must always confirm the gap, even if you gap one and set it down, check it. You sometimes drop them and close up the gap. Check them and recheck them to be sure. It is easy and fast and free. I sometimes find them all set and sometimes all wrong.

Title: Re: W9DC Spark Plugs
Post by: Benz Dr. on August 14, 2009, 00:08:18

I think they're pre set at .032 and I leave them there. Having the gap too close will cause a  missfire.

Title: Re: W9DC Spark Plugs
Post by: 66andBlue on August 14, 2009, 00:27:16

W9DC: pre-gapped at 0.9 mm = 0.0354 inch
Torque: 25 Nm = 19 ft. lbs.

Title: Re: W9DC Spark Plugs
Post by: Dash808 on August 14, 2009, 04:47:34

I just put a set of NGK BP5es in.  They were all gapped at .35 out of the box. 
Just right and runs great. 
 

Title: Re: W9DC Spark Plugs
Post by: mdsalemi on August 17, 2009, 15:46:48

On the spark plug topic...

How do you know if you are running the right plug?  I have NGK BP6ES; how do I know if this is the right plug, or one heat range hotter or colder might be better?

Obviously the thing to do is try--but assume for a moment that I have three sets of plugs, my BP6ES, and whatever the next hotter or colder plug is.  What are the symptoms/running characteristics I would see with a plug out of the right heat range??

Title: Re: W9DC Spark Plugs
Post by: Dash808 on August 17, 2009, 21:53:16

According to NGK: 
Spark plug tip temperature must remain between 500- 850 deg C.   One heat range hotter or colder = 70-100 deg C.   
Temps <500 deg will lead to fowling and misfire. 
Temps >850 deg will lead to preignition/detonation.

For best results learn to read the plug. 

A good read:

http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US (http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US)