I recently bought a 2011 s204 c350 (N/A M276 engine) here in europe. After buying, I directly changed the oil, filters and spark plugs myself. During replacement, I did not do any torque adjustment (no native speaker, don't know the exact wording) but only used a normal ratchet wrench tightening the plugs. I drove around 2000 km (1300 miles approx.) without any issues but stumbled upon various forums about how important it is to torque down the sparkplugs with 23 nm (info from MB) such that is is indexed correctly (apparently required for direct injection engines, which the M276 is one of). Now, I was wondering how likely this damaged my car since I drove 2000 km after the replacement and if I am screwed or not. The car runs fine but now I am afraid I might have initiated some big future problems to the engine. Should I replace the plugs with new ones and tighten it with the torque wrench this time?
By the way, Bosch spark plugs specially made for the M276 engine are used instead of Mercedes Benz part. I know that some of the forum users strongly oppose Bosch spark plugs due to its quality, however I noticed that this is more the case for in the US.
I wouldnt worry about it if it is running fine. I dont have a DI engine but read that the plugs do have to be indexed, which is done installing with the proper torque setting.
Best way would be to buy a torque wrench and re-install them.
You can either remove them then re-install using a torque wrench, or remove and follow the directions below for installing without a torque wrench.
I recently bought a 2011 s204 c350 (N/A M276 engine) here in europe. After buying, I directly changed the oil, filters and spark plugs myself. During replacement, I did not do any torque adjustment (no native speaker, don't know the exact wording) but only used a normal ratchet wrench tightening the plugs. I drove around 2000 km (1300 miles approx.) without any issues but stumbled upon various forums about how important it is to torque down the sparkplugs with 23 nm (info from MB) such that is is indexed correctly (apparently required for direct injection engines, which the M276 is one of). Now, I was wondering how likely this damaged my car since I drove 2000 km after the replacement and if I am screwed or not. The car runs fine but now I am afraid I might have initiated some big future problems to the engine.
Should I replace the plugs with new ones and tighten it with the torque wrench this time?
By the way, Bosch spark plugs specially made for the M276 engine are used instead of Mercedes Benz part. I know that some of the forum users strongly oppose Bosch spark plugs due to its quality, however I noticed that this is more the case for in the US.
@TimC300 is technically correct. But you didn’t damage anything. There is a 45 degree tolerance on the indexing. If you have tightened all the plugs approximately the same, and the engine is not misfiring after 2000 km, I recommend no action at all.
Bosch spark plugs are fine. That is what Mercedes used in my 2015 GLK350 at the factory.
I wouldnt worry about it if it is running fine. I dont have a DI engine but read that the plugs do have to be indexed, which is done installing with the proper torque setting.
Best way would be to buy a torque wrench and re-install them.
You can either remove them then re-install using a torque wrench, or remove and follow the directions below for installing without a torque wrench.
I would NOT follow the Bosch website instructions as they are more for non-GDI engines. Personally, I would reinstall the plugs to the correct torque setting. I know it is a pain to remove the intake plenum, etc., but I would always worry about the "perfect storm" of conditions that will cause damage.
I found that the Bosch plugs were a little "sloppy" when it came to indexing, even though they are supposed to be the exact same as the Mercedes plugs. I actually use NGK 96427(SILZKFR8G7S)plugs which indexed nearly perfectly. My engine is FLEX FUEL capable. These plugs are: Specially indexed spark plug. Do not use alternatives. OE Spark Plug Is High Ignitability. For Optimal Performance, Replace With High Ignitability Spark Plugs.; OE-Recommended Gap: 0.028"
Here is a good video to watch on indexing the plugs:
I remember no mention in the 2015 GLK350 (M276 NA) owner’s manual about damage to the engine from not indexing spark plugs. The video shows, what I assume, the manual for the E63 AMG (M157) noting possible damage. The purpose of indexing as I know it is so that the DI injector spray is not dispersed by the spark plug electrode. Since the fuel charge is quite lean in these engines, that could lead to misfiring. Misfiring will cause an over rich exhaust stream which could overheat and damage the catalytic converter. Maybe that’s the damage that the manual in the video refers to.
Racing engines are always indexed because even a single misfire could lose a race.
As an additional note, there are spark plug washers of varying thickness available so that the washers don’t have to be sanded down to size.
'm not claiming to be right, but I've never torqued any spark plugs—mainly because I don't have a torque wrench. Even so, my Toyota, C250, and VW have never had any issues related to improper torquing—knock on wood.
I'm not sure ANY Operator's Manual would discuss indexing spark plugs. But, please see the attached document.
That’s about what I know plus the non specific engine damage comment. Engine damage from backfires at high RPM and high load maybe. Doing it right is never wrong. Personally, I’m like the guy in the video. If they say 45 deg is okay, I will do 15 deg or less if I am going to do it at all. I have an indexing jig that I use. I even indexed the M271 and in the 70s indexed HiPo carburetor engines.
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