Indexing Spark Plugs

[grober]

Have to confess I had never come across this before. Refers to the positioning of the spark plug ground electrode WRT the position of the direct injector in the cylinder head. How crucial this is WRT engine power /economy/emissions --if at all? I don't know but seems to apply to direct injection petrol engines and effect the space charge/ multiple injection aspect of these engines. Positioning seems to be dependent of plug threading and plug installation torque- meaning installation and using the correct plugs is important.
Discussed here - perhaps some MB techs might comment?
Indexing spark plugs

 

[RichardF]

I've done this for yrs, not just Di either. I pop the heads off on plug change day to check, reassemble with the plugs insitu

 

[E55BOF]

If the plug has only one starting point in the thread, and I rather think that, nowadays at least, they all have, then provided the correct MB-spec plug is used and it is torqued correctly, the indexing cannot be other than correct.

You don't have to buy a set of MB plugs and pay extra for the MB boxes, though; if you know the OE manufacturer's part number, just buy a set of those.

 

[grober]

Here's a video of how to do it WITH NON INDEXED PLUGS on an EVINRUDE OUTBOARD [ TWO STROKE] it does outline a method whereby you could check ground electrode orientation wrt injector position by marking the plug/plug socket +extension. Indeed with deeply recessed plugs this would be the only visual check you could do.

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[pcthrillrider]

it dont matter which way plug is a spark is a spark bang

 

[Blue30]

Maybe if you’re looking for that last 0.01 bhp on a race engine you could kill an hour doing this....

I did it on my old Micra back in the day

 

[190]

I've indexed the plugs on the bike for many years. I doubt there is any HP gain but it does achieve one thing in that it makes that aspect of ignition on both cylinders the same. Having everything as far as possible on a twin cylinder engine the same is something you are always striving for to achieve smooth running.