R129 SL500 - 1996 Spark plug change

[R129mine]

Hi
I am replacing the spark plugs in my R129 from 1996 (SL500) and have removed the old ones installed by the garage in 2017 as part of my routine maintenance this weekend. I have never replaced the spark plugs in the R129, but have replaced them on my other cars in the past

The plugs have some burn marks on the white of the spark plug where it meets the metal

The old NGK plugs (BCP6E) had a gap of 0.035inches.
I bought the new spark plugs of the slshop and they are Bosch and the gap is about 0.025 inches
Mercedes-Benz Spark Plug - 0031596703 which is BOSCH FR8DC (7927) and are preset to 0.025/6 inches


Should I change this to match the old ones (0.035) or leave it as is (pregapped) ?

I ran the engine and it is idling fine, about to take it on a test drive but all seem to be running smoothly

Thanks

 

[ALFAitalia]

I'll be back after I've translated that to mm!

 

[Doodle]

Leave them as they are, the plugs you've removed are incorrect anyway. They're non-resistor plugs which are intended for the earlier distributor-equipped cars - the caps, leads and rotor arm contribute to the preset resistance of the ignition system (around 4kΩ)

Those elements of resistance don't exist in the coil on plug setup, so it's provided by the plugs instead (the R in the spark plug code).

 

[R129mine]

Leave them as they are, the plugs you've removed are incorrect anyway. They're non-resistor plugs which are intended for the earlier distributor-equipped cars - the caps, leads and rotor arm contribute to the preset resistance of the ignition system (around 4kΩ)

Those elements of resistance don't exist in the coil on plug setup, so it's provided by the plugs instead (the R in the spark plug code).

Thank you
All sorted and running nicely. I did hear about the older engines needing resistor less spark plugs and good to know I am all set for next 30k. Currently at 163k

 

[Will]

FWIW, I think the correct plugs from the main dealer are cheaper than SL shop!

 

[alabbasi]

I think the gap size from manual is 0.8mm or 0.031, a lot of people say that gapping to 1mm or 0.040 makes the M119 run better. 0.035 is right in between so I don't think you'll have a problem.

 

[slade1]

Changed the plugs on CLK M272 years ago, out of the box no adjustment.
They have done close to 40K miles and are still OK.