Different spark plugs on the same engine problems

[rostanlin]

Greetings,I need to know what problems can cause the use of different spark plugs on a same Gas Engine. Eg. I have seen the use of Champion RM77N and Champion D14N at the same time on a Waukesha L7042GSI with Altronic III ignition system. I would like to know the consequences of this practice for the ignition system parts and for the cylinder/cylinder head as well...

 

[Lou Scannon]

Ask the engine manufacturer. No one here can answer that without knowing the exact details of the spark plugs and the engine. In general, engine performance, knock sensitivity, and/or spark plug life will be unpredictably and probably negatively impacted if spark plugs other than those recommended by the manufacturer are used. If different plugs are recommended interchangeably, then it is probably fine.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[IRstuff]

I would think that a decent IC engineering book would discuss this. There's basically gap and position in the cylinder. Unless, the plugs are intended as direct replacements, there will be differences in ignition profile that's different than what the designer intended.

TTFN
faq731-376

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[BrianPetersen]

Thread diameter and reach are the same. The hex diameter is a bit different (it will need a different socket to install/remove). The RM... is a resistor plug, the other one is not (affects electromagnetic interference of nearby electronic equipment).

Only explanation I have is that someone screwed up (or ran out of stock of one and had some of the other on hand). There's no rational explanation that I have for intentionally using different spark plugs in different cylinders of the same engine.