Discover
Joined: 26 Feb 2007
Posts: 429
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 Posted: Wed Dec 28, 2011 8:09 am Post subject: Spark Plug Repair! |
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I googled "Slick Magneto Spark Plug Resistance" and got some interesting links. I never thought about replacing the resistor in my Champion plugs! Might try that today. Take the massives out of the engine and use their "good" resistors in my fine wires...
http://www.aircraftmagnetoservice.net/id18.html
A new resistor type plug should read between 800 and 1200 Ohms
Remove and replace any plug that reads 5000 Ohms or more.
http://www.sacskyranch.com/eng11.htm
2. Incorrect spark plug gap(s). Fouled spark plugs. Broken spark plug ceramic. Too much spark plug resistance, normal 1,000 ohm, too much is probably 10,000 and greater.
This very interesting, from a Lancair list guy who talked to a magneto tech:
http://lancair.net/lists/lml/Message/56111.html?Language=
| Quote: | Then we started talking about spark plugs: I mentioned my plane has Champion fine wire plugs. He said all plugs have an internal resistor, and for some reason the resistance of many Champion plugs seems to increase as the plug ages. Once the plug has been cleaned, the resistance can be measured with a standard ohm meter between the center electrode and the connection inside the plug barrel -- all new plugs should have a resistance somewhere around [url=tel:800%20-%201200]800 - 1200[/url]ohms. If the resistance ever measures above 5000 ohms, the plug should not be used. The fellow told me plugs having too high of a resistance can/will cause misfiring and potential problems with the magneto coil and or plug harness. A spark plug bomb tester might show this plug as good, so the ohm meter test should always be performed every time the plugs are serviced.
Unlike an Autolite plug, a Champion spark plug resistor can be changed. Look inside the barrel of a Champion plug and notice the slotted screw. Remove the screw and the resistor will fall out: it looks like a slug of carbon about 1/2 inch long and maybe 1/8 inch diameter. You can put the ohm meter on either end of this slug and measure the resistance -- this is the element that needs to measure from about 800 to 5000 ohms. The resistor is apparently common among all Champion plugs so he recommended visiting your pile of old plugs; removing the resistors; and saving the resistors that measure "good". When you run across an otherwise servicable plug whose resistance is too high you can change its resistor for one from the "good" pile. He says this can cure a host of otherwise mysterious "rough running" problems and forestall future problems.
He said some Reno racers remove the resistor and replace it with a piece of copper wire to get a much hotter spark for racing. Says it wears out the spark plugs very quickly -- but does make a performance difference. Is this true?
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http://mechanicsupport.blogspot.com/2009/09/rough-engine-on-left-mag-nothing-you-do.html?m=1
Spark plug terminal well showing arching lines. Plug lead is arching to ground by way of the plug metal shell. Replace plug. At the bottom of the well there is a contact. Check spark plug resistance by placing 1 end of the ohm meter lead to this contact and the other end of the lead to the center electrode on the firing end of the spark plug. Resistance should be 800 to 1200 OHMS. Replace any plug above 5000 OHMS.
 This is what the resistor looks like inside a Champion REM40E spark plug.
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