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Which Hex size for NGK CM-6 plug? (OS GF40 Plug)

Old 07-05-2018, 09:24 AM
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Eindecker_pilot
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Question Which Hex size for NGK CM-6 plug? (OS GF40 Plug)

Hello,
Background:
- I have an OS GF40 on a quarter scale model and I love this engine. I'd like to have a spare spark plug in my field box in case I need it. I also need the right size spark plug wrench for this plug.
- The spark plug for the OSGF40 is an NGK CM-6 plug.
- I have ordered the replacement plug from Tower (where I was directed by OS telephone tech support and they were not able to answer this question so I am posting it here). Tower did not sell the wrench that goes with this plug, nor did their tech notes specify the hex size. Here is my question:

My Question:
What size spark plug wrench do I need to use on the OS GF40? I have done an online search on the hex size specs for the NGK CM-6 and inexplicably I see two hex sizes for the same CM-6 plug (NGK 5812). This is my problem. Which wrench hex size fits the OS GF 40's plug (OS part number 7169000 is essentially the NGK part number 5812)? Why on earth does NGK make two different hex sizes for the same model number? Here are the examples I've come across.

This one says 5/8" hex size:
https://www.ch-ignitions.com/dle-da-...o-moki-os.html

This one says 9/16" hex size:
Spark Plug, NGK CM6, from Chief Aircraft, ca-ngk-cm6 - Chief Aircraft Inc.

These two specs can be found at several other retailers.

Thanks,
Greg
Old 07-05-2018, 10:29 AM
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BarracudaHockey
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Interesting......

I have a pile of CM6 plugs and they all use a 9/16 plug wrench.
I have one of these I keep in my field tools http://www.taildraggerrc.com/spark-p...m6-spark-plug/

Last edited by BarracudaHockey; 07-05-2018 at 10:34 AM.
Old 07-05-2018, 04:00 PM
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Eindecker_pilot
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Yeah, its crazy that the same model number has two different specs. It will be a surprise as to which version I get!

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