Pagoda SL Group
W113 Pagoda SL Group => Electrical and Instruments => Topic started by: perry113 on March 15, 2016, 16:31:30
-
It's time to replace my spark plugs for proactive reasons on my 65 230SL.
I have a good supply of the original W7DC bosch spark plugs.
What is the correct or best recommended gap to set the new ones at? I am still running points with the original distributor.
Many Thanks
Peter
-
I set mine to .035" The tech manual has .034"
-
I ran W9DC when they were still available. These are a bit hotter than the W7DC and most of the time you will need the extra heat range just to keep from fouling out during cold starts. If your engine has perfect compression, and you fire it up and drive away without letting the engine idle while cold, you should be OK.
I've been using the factory setting of .032'' on NGK BP5ES plugs. Is there some benefit to a slightly larger gap?
-
I'm not sure of any benefit or lack of from a larger gap. I have always set them at .035 on my 61 220 S and 280 SE 4.5. I just continued the practice on my 230 SL. All three cars ran well at this setting.
-
With the Pertronix electronic system installed, along with their more powerful "Flamethrower II" coil, they recommend increasing your plug gap by .005 over factory spec. As some folks on racing and other forums note, perhaps simply ad hoc without scientific testing, is that the hotter the spark the more you can increase the plug gap. With a larger gap, you get a physically larger spark which in theory would lead to more complete combustion. I opened mine a bit, perhaps .003 and the engine runs and idles fine so I don't mess much with it. I did go to a hotter plug per Dan's recommendation and I think that is better. I had the BP6ES and went to the BP5ES.
-
Spark plug gap is an interesting balancing act. Michael is right that the larger the gap the higher the firing voltage and the hotter the spark. Of course all things have their limits and when the spark gap gets too wide the current(not the voltage) starts to drop and the spark becomes unstable. Another drawback of too wide of a gap is that the voltage tries to find the easiest path to ground and you might find that that path isn't across the spark plug gap but through the side of the spark plug wire or through the ignition rotor or cap. All that being said on an engine with reasonable fuel control(fuel injected) I would tend to stick pretty close to .035.