Postby Peter Clare » December 13th, 2013, 7:10 pm
I don't think you are going to get an honest answer on this John, but based on past experience in engine manufacturing industry it will probably as follows.
Champion would have had an agreement with Zenoah to supply spark plugs in which case they developed a plug ideally suited to the engine - the 82 in the plug designation indicates " industrial and special applications" . In that instance Zenoah will have agreed to exclusively recommend Champion.
The 6 in the NGK CM-6 designation indicates " heat range 6 " and as it is not possible to relate this to the 82 in the Champion we will never know the difference.
Unless someone comes up with extensive experience using the NGK plug on this engine it's probably best to take Zenoah's word for it although NGK plug application charts do list the CM6 as interchangeable.