Re: 1964 mercury 9.8 spark plugs
I think it's a Champion J8C. But you can double check that on any number of web sites- I don't know of this IBoats site has it, but you can check at the oldmercs.com or mercruiserparts.com websites, and probably sparkplugs.com for cross reference info.<br /><br />I don't know the gap. Wild guess would be .030<br /><br />I bought a OEM owner's manual for my old merc 110 and it has spark plug, gap, and other simple maintenance info. I got it at maxrules.com, which is a great company, but again, there's any number of sources. I also bought Seloc (first) and OEM (later) shop manuals. Both seem to work fine.<br /><br />For what it's worth, I've found that the older Mercs spec. Champion plugs and I believe many newer ones spec NGK. I always like to try to get the brand spec'd having been told that the "equivalent" plugs by the various manufacturers are not really totally equivalent. What difference this makes for a 9.8 HP motor, I have no idea.