Topic: Lesson Learned: Reddit Posts Show Why Spark Plug Changes Are Best Left to the Pros

[PJungnitsch]

I dunno how big a deal this is, maybe it's just certain engines or something.

When we were shopping for an SUV a few years back we asked a mechanic friend about Mercedes and he just laughed and mentioned this. He showed me how he marked the ground strap location on every sparkplug with a sharpie and double checked it ended up in the right location.

[rrocket]

I dunno how big a deal this is, maybe it's just certain engines or something.

When we were shopping for an SUV a few years back we asked a mechanic friend about Mercedes and he just laughed and mentioned this. He showed me how he marked the ground strap location on every sparkplug with a sharpie and double checked it ended up in the right location.

I remember this a being a motorsport thing back in the day when I was racing bikes. Apparently it allows for peak combustion via superior flame propagation.

Supposed to eek out about 1 percent in highly tuned engines.

[EV Dan]

My Evinrude outboard DI motor calls for Indexing.  I just might do it now after this thread.

How is it done? Let's say e.g. it's a 4 pot engine. If I get 8 plugs in total and then try them on each cylinder until a desired index is achieved, would this accomplish the task?

[EV Dan]

More on spark plug indexing from an NGK guy:
https://www.youtube.com/watch?v=34LSZF_wN3U
From what I have gathered, the plug opening should be within 90 degree window from the GDI injector, in modern engines that is. In other words, the ground electrode should not be in the way between the injector and a spark. It can be done by tawking torquing of OE plugs to MFG specs or in my opinion it would make sense to mark the top of the socket with where the spark plug opening is so that you would know exactly how the SP is being oriented during torquing, since there is always a MIN-MAX torque specified for every application.