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Spark plug resistance?

Janekom

Janekom

Well Known Member
Patron
I always test the spark plug resistance during inspections and have been taught to replace it when the resistance goes over about 2K. I am talking about the usual Champion and Tempest plugs.
My question is - if the resistance is way too high or open circuit, but you do not notice it during a power check or during normal flight, what effect if any will it have? I am specifically wondering about a higher EGT should one try to fly LOP. Thank you
 
I had a helicopter that passed the mag check, but about a minute into the flight started running rough. turned out to be a high resistance plug. I think it has to do with the high cylinder pressures at full power and the high resistance would cause a misfire. YMMV. Ben
 
Janekom said:
I always test the spark plug resistance during inspections and have been taught to replace it when the resistance goes over about 2K. I am talking about the usual Champion and Tempest plugs.
My question is - if the resistance is way too high or open circuit, but you do not notice it during a power check or during normal flight, what effect if any will it have? I am specifically wondering about a higher EGT should one try to fly LOP. Thank you
Click to expand...

500-3000 ohms for new plug
500-5000 ohms for used plug

I had a plug with open circuit and it only showed up as a high EGT when leaned. Fired fine on ground mag check but was not firing at all when mag checked at cruise. Engine ran smooth.
 
I have found the best range for all around operation to be between 900-2100 ohms. Yes, I know the specs are 500 ohms to 5k ohms, but hot starts especially seem to not be a problem with the plugs in the range I mentioned. I test everyone new and they all seem to average around 1100-1200 ohms.
vic
 
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