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Spark Plug Index. M276 3.0 TT - If only the block's thread machining is accurate !
I am dissapointed............
M276 3.0 Turbo. 20,000 KM plug life. Still looks good, but I change them anyway.
Once upon a time, MB warned the importance of Spark Plug Indexing............. original files attached, both.
23Nm is nothing, it is a very low turning torque. It will take at least 60 ish Nm for my engine if I were to pursue merely the earliest edge of the target 45 degrees target window as shown on MB warning document.
The question is, do I follow only the 23 Nm Torque value or do brute force to get the earliest edge of the 45 degrees target window ?
23 Nm is equal to a simple "hand tight" but with rachet held in the middle to gain no leverage ( no human fingers can go into the hole for spark plug ) and add 7-10 degree more clockwise from that stop of HAND TIGHT, that is 23 NM.
I use 2 torque wrench and I use the AC Delco digital torque meter/adapter with a calibration certificate to confirm 23Nm.
01. Why the hell the AP15.10-P-1580EW of 2019 print has no warning on the indexing ?
02. Cylinder 1 to 3, I applied 24.5 to 27 Nm. This Bank 1 is the "better" bank than the LEFT bank 4th to 6th cylinder.
03. I use original MB spark plugs. Always. Only this time I marked them all to see how indexed they can be.
RED MARKER LINE POSITION
==============================
1st cylinder result.
ABOVE : If my red marker line can get to 6' oclock or 180degrees, that means my plug is aimed directly to injector nozzle and that is gold standard , if possible. Dream on.....
BELOW : Red marker line "aiming" position viewed from inside combustion chamber. Borderline result, almost touching the edge of the 45 degrees target window...ALMOST.
========================================
Cylinder 2
ABOVE : Female thread condition at engine block.
3rd cylinder is very similar to Cylinder 1 and 2, hence I said, the right bank is the better bank.
BELOW : The moment I saw a hand tight angle is so bad, I knew the 23 NM will do little to get more clockwise turn.
==============================================
Cylinder 5 and 6
5th and 6th at 23 Nm. So bad for 6th and 4th.
The spark plug showned by MB look fat. Is the M276 3.5 NA uses this fat plug ? Mine seems a mini version. 14mm socket it uses. Also the top contact point is different.
So what do I do ?
AA> Raised tightening torque , probably to 60 Nm ish....to get RED MARKER to hit 5 o'clock at least ... and risked of damaging the aluminum female thread at engine block come spark plug change next 20,000KM.
or
BB> Ignore the indexing Warning, as there is no more of such warning for 2019 edition of the AP15.10-P-1580EW
The simple truth is, if only MB machined the female thread properly, this post will not exist.
The difference between LEFT and RIGHT bank is the real SAD truth.
Same block and probably done by the same robot thread making machine, but the result is almost 7 degrees OFF and consistently off for LEFT bank.
Next time anyone of you owning 3.0 version M276 do a spark plug change, please do the same marking and share. Thanks
Indexing is surely good by logic of air flow from inlet valves to exhaust valve and a spark plug's needle is to point to intake valve as 12 o'clock as MB wanted and
the L ground of the plug ( is that even a proper name , the L ground ) to be at 6 o'clock.
Sure there is a swirling turbulence to be taken in to account as efficieny assist.
Moving around plug index:
Do you think the fuel trim would register any difference if you'd put a double washer on one bank to mess up indexing -or try to fix your bank that's out of index ??
When I changed my plugs, I used this plug https://www.boschautoparts.com/en/au...tId=ZR6SII3320 I noted that the Bosch website says: OE-matched spark position for compatibility with new Gasoline Direct Injection (GDI) technology, so I bought them.
Just wondering if the indexing is any better/different vs NGK??
Buy MB spark plugs from the dealer and install to 23Nm. Done. Indexing has been accomplished by virtue of cylinder head thread machining, spark plug thread rolling, crush washer and torque spec.
You could be right, Chassis, but these threads showing the plug indexing is "wrong," do bother me ...
This fulfills our curiosity with reality.
Benz publishes white papers about the ultimate combustion with indexed plugs, stratified mixture, multi-spark... but their heads are shown to be +/- compliant 🤣
Last edited by CaliBenzDriver; 06-27-2021 at 03:43 PM.
Spark plug marking and worrying about indexing is often brought on by people looking to save money by buying non-dealer, non-OEM spark plugs. MB spark plugs from the dealer are expensive. All MB owners know this and accept it when they bought their MBs. And yet people look to save money on spark plugs.
Non-OEM spark plugs are shown in the well-distributed report by MB to result in improper indexing. And, in the example shown in the report, spark erosion of the valve perimeter can result. This is because aftermarket spark plug thread tolerance and crush washer tolerance are not the same as MB OEM plugs from the dealer. It's impossible for this to be otherwise, if the aftermarket plugs are made other than by the OEM supplier.
So the options are to pay the price at the dealer, install to 23Nm, and have properly indexed plugs. Or save some money on spark plugs, and fret and fuss about indexing, and continually wonder if you got it right, all the while risking spark erosion of the valve perimeter.
This fulfills our curiosity with reality.
Benz publishes white papers about the ultimate combustion with indexed plugs, stratified mixture, multi-spark... but their heads are shown to be +/- compliant 🤣
I agree, I get what Chassis is saying, but the proof is in the pudding...
S-Prihadi and Duckstu have had OE plugs NOT index per MB own published guidelines. So either:
* manufacturing defect in the plugs purchased
* manufacturing defect in the engine of the two users
* MBs guideline are not accurate
* doesn't matter
No idea, the 1st plug change at 10,000KM was done at my friend's workshop, torqued ....yes. It was not index-ded for sure, as there was no marking made by them.
Also original MB plugs. I always use original parts.
It was a good 20,000KM run including 20 laps track use and 10 hours x 2 non stop long distance.
Today the car is at 31,000 KM.
To believe MB blindly and not marking the plugs when doing 23Nm is foolish, that is the reason I marked it as I needed to see if I am within the 45 degrees window or not.
If and when the female thread machining is accurate by MB and I get within the 45 degrees window, only then no more marking required at future plug change , that simple.
I think I will try to clean the female thread at the engine block from the carbon residue, I am still figuring out how best to do it safely.
23 Nm is too gentle and carbon on the female thread may contribute, but I doubt I can get any better by +5 degrees clockwise from where they are now.
23Nm by logic is the force needed to mate-squeeze the copper gasket of the plugs. Spark plug is not a bolt, so tension is not the target, copper sealing is the target.
The reason before I torqued to 23Nm... i use hand tight method is to confirm maximum thread insertion and to feel for any unwanted resistance.
The moment the hand tight is achieved, that confirmed that my plug's copper gasket has reached its mating surface at engine block.
Cylinder 4.
Thread cleaning......
Use old 20K KM plug, cleaned its thread well.
AA. Spray carburator cleaner to plug's thread to wet it till it dripped.
Insert the used plug into cylinder 4. Use fingers tight only till copper washer hit home. Screw-in screw-out the plug.
Take out plug, clean thread and redo AA.
AA done 3 times.
BB. Spray carburator cleaner to plug's thread to wet it till it dripped.
Insert the used plug into cylinder 4. Use fingers tight only till copper washer hit home. Use wrench to add a bit more tightening torque, under 10 Nm.
This time let the carburator cleaner works longer. Plug threaded into block varies between 3, 5 and 10 minutes. So total 3 times.
Result :
Same old same
The tool
Next step.....
Swallow the pain pill, accept the fact that MB did not machine my 3.0 plug's female thread properly .... and wait if my piston will melt at it edges or not... at 50,000KM or next 20,000 KM.
So if I get this correctly the special OEM plugs are indexed nearly like NGK. They miss the mark by about 90°, almost a quarter turn.
Check out this fix:
How about swap the solid OEM washers for new crush washers (like regular plugs) that will be taller and help bring out your plug by 90°.
I don't think a double washer is recommended so you got to find a kit of assorted washer thickness... from direct injection racing shops dealing with indexers.
Acceptable index range:
Is serious indexing really going to make any difference at all or NGK fair equals ??
What is considered acceptable... is everything besides electrode nearest to injector ok??
Make sense to use thinner copper washer.
I do not think 23Nm can crush regular copper washer, no power.
I will measure with my pitch gauge to see its thread count and spec...........or
I can remove from my old plug the copper washer and do 23Nm and see how many more degrees I get without copper washer and then
I reverse calculate the required NEW copper washer thickness to gain 12 degrees more clockwise turn.
First I must get proper supporting data for minimum allowable copper washer thickness for a spark plug duty and for turbocharged engine.
My turbo is a polite one at 11.6 psi only or 0.8 BAR.
I never bought indexing as anything other then a reason the MB dealer gets more $$$
NOTE: My plugs are still the original ones.
What do other manufactures with DI engines say?
Heck I think all of them have DI engines now.
Would be very costly to ensure plugs and heads work everytime for indexing from a manufacturing point of view.
The cylinder head plug cutting tool would have to be indexed with respect to the first thread cut - which if you ever cut threads is a PIA.
Also is not eh Fuel injected just prior to spark to give the fuel time to mix well with the air so it is uniform inside combustion chamber and burn better and cleaner?
once well mixed does it really matter where electrode is?
Only super duper race engine builders care....trying to get every tenth of a second out of car.
What is the latest MB DOC?
What is this doc discussing indexing and what is copyright year?
What does it say? Maybe they dropped it realizing all it did was cost a waste in spark plugs dealers threw away since they did not index properly.
Looks like a lawyer wrote it as it is not clear on WHY you have to index...
just index so you do not ruin cats which means index so you do not get misfires.
As too much raw fuel dumps from misfires kill cats.
I never bought indexing as anything other then a reason the MB dealer gets more $$$
I dont think MB is that naughty. The indexing thingy was dated June 2014, that is before E400 3.0TT non hybrid was introduced in the USA, I think. USA got the E400 in 2015 right ?
All degrees mentioned is looking at spark plug from outside the engine and 12 o'clock as 0 degrees, red marker at plug at various angle,
example cylinder 4 I estimated at 80 degrees.
If red marker at plug can hit 180 degrees or 6 o'clock = BEAUTIFUL
Angular Test, No Copper Gasket, but 19 Nm only. Me don't want to damage me block
So, M276 3.0 TT owner, have a go at the thinner copper gasket solution if you guys ever need them.
For M276 3.5 NA, if your plug thread pitch is also 1.25mm, you can use the same base calculation for modified thickness, if ever you verify your OE/MB plugs do not meet the 45 degree beauty window MB suggested.
Folks the MB plugs+crush washers are not special. They are designed for the engine. Tolerances in this situation make or break the electrode position.
Third party spark plugs+crush washers are not made with MB tolerances.
Pay the money at the dealer for MB plugs.
Just pay it. It's amounts to nil in the total cost of ownership.
Hate to be that guy... but the OP used OE plugs (i.e., Mercedes). Duckstu used OEM and Aftermarket Bosch plugs (two different P/Ns) and a single OE/MB plug, I believe none of them index "correctly".
I'll bet I could give this job to 5 experienced technicians with torque wrenches (and calibration services for those tools that I can't afford) and they would come up with five amazingly different angles and at least one tech wouldn't have bothered to clean/chase the threads.
I would have rather seen them mark at the factory the electrode position on the plug insulator and then give a "clock map" of the heads in the manual. That way, you would easily know that you were in the ballpark.
I'm sure that MB has done computer modeling as well as high speed photography of the combustion patterns in action. I seriously doubt that this is a "gimmick" to sell expensive plugs in this new, very complicated combustion era.
I never bought indexing as anything other then a reason the MB dealer gets more $$$
NOTE: My plugs are still the original ones.
What do other manufactures with DI engines say?
Heck I think all of them have DI engines now.
Would be very costly to ensure plugs and heads work everytime for indexing from a manufacturing point of view.
The cylinder head plug cutting tool would have to be indexed with respect to the first thread cut - which if you ever cut threads is a PIA.
Also is not eh Fuel injected just prior to spark to give the fuel time to mix well with the air so it is uniform inside combustion chamber and burn better and cleaner?
once well mixed does it really matter where electrode is?
Only super duper race engine builders care....trying to get every tenth of a second out of car.
What is the latest MB DOC?
What is this doc discussing indexing and what is copyright year?
What does it say? Maybe they dropped it realizing all it did was cost a waste in spark plugs dealers threw away since they did not index properly.
Looks like a lawyer wrote it as it is not clear on WHY you have to index...
just index so you do not ruin cats which means index so you do not get misfires.
As too much raw fuel dumps from misfires kill cats.
i had a Hyundai 2.0 Turbo engine (direct injection) that ran on regular, and I don't recall any comments on indexing in the official service manual.
HOWEVER, the part number for that plug changed at least three times in eight years and now I wonder why. Those plugs were VERY expensive from the dealer, which I found odd on a relatively pedestrian car.
The reality is, as long as the gap is exposed to the injector (not 180* off), it will be fine.
The real reason for the plug alignment is for the stratified injection mode of the DI engines, when it's firing multiple small pulses of fuel and multiple sparks, the flame front needs to be free to travel across the middle. That's about it. What the OP ended up with will be just fine, will not damage anything, and is probably the way they all look when coming out of the factory in all honesty, although I haven't checked any OEM ones, we did mark the sockets to check it a few times roughly and never had super accurate results.
I would have rather seen them mark at the factory the electrode position on the plug insulator and then give a "clock map" of the heads in the manual. That way, you would easily know that you were in the ballpark.
Sure, this is all easy as long as the start of the female thread at the block, the zero point ... is dead on when machined by the robots/human at the factory.
The rest will automatically falls in line at 23 Nm or whatever the set torque value the designer calculated to maintain good thread tension and sealing of the copper washer.
Thread Pitch is not rocket science. The key is consistency of the machining workforce at the factory.
06-27-2021, 10:44 AM
) to be at 6 o'clock.
at 50,000KM or next 20,000 KM.
So, M276 3.0 TT owner, have a go at the thinner copper gasket solution if you guys ever need them. 
