| [GMCnet] The Correct Spark Plugs Mean A Lot [message #247801] |
Fri, 18 April 2014 01:00  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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I got interested in what the correct spark plug to use in my 6,000 Watt Onan that's in our GMC. As the two 78 Royale's both appeared to have the wrong plugs. The first clue was that all the plugs were too short on the threaded portion of the plugs. And I found 3 different plug numbers installed. Called 4 GMC owners. Asked them to go check their Onan spark plugs. None of them had plugs that matched anyone elses plugs. Then put something out to the form. Got some list of plugs to use. When to Auto Zone with list in hand. Found some of the plugs had the tapered sealing surfaces that were on the interchange list. Those are definitely wrong. Checked our GMCMI parts book. So to make absolutely sure that I had the correct plug that Onan called for in our generators. I ordered two spark plugs at my local Cumminns/ Onan dealer. So the absolute CORRECT spark plugs are Champion brand RH12. Now I have heard comments made at times that this, or that brand of plugs aren't very good. Whene
ver I've dug into plug failures. It's always been a case of the wrong plug for that application. There are lots of different plug numbers. There is a big reason why. In the next day or two. I'[ll list some of the plug number. And what the numbers, and letters mean. And explain how to properly index your spark plugs to the combustion chamber. For the best fuel efficiency by having a cleaner flame front at the time of ignition. I index all my plugs to the combustion chamber.Bob Dunahugh Member GMCMI78 Royale4 Real COPO Yenko's
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