Anyone have spark plug cross reference?

[Crappie_Fan]

My Evinrude is a 74 Model 25452m, the plug it has had in it was a J4C, Champion websites says it should be a J8C. I need to get 2 plugs todays but the local boat shop isnt open, is there any cross reference for those plugs, like NGK or some other brand. And does anyone know exactly what plug this motor came from the factory with?<br /><br />Thanks

 

[Dhadley]

Re: Anyone have spark plug cross reference?

Stick with the J4C. And stick with Champions in an OMC motor.

 

[ron7000]

Re: Anyone have spark plug cross reference?

sorry, can't help you with the plug the motor originally came with, but I can help you with cross reference.<br /><br /> http://home.att.net/~ngkaz/wsb/html/view.cgi-home.html-.html <br /><br />download the NGK 2.0Mb cross reference, an excel sheet. If you don't have excel, do a google search on excel viewer and you should be able to download a free viewer.<br /><br />I've used this excel cross reference for the past 3 years. It has changed over time, but has done me well for both cars and boats, outboards included.<br /><br />J4C is a 14mm thread spark plug with a gasket washer for a seat as opposed to a taper seat (no washer), is 13/16" (0.8125") hex size for the spark plug socket, has a 0.375" reach.<br /><br />Champ to NGK cold to hot heat range<br />J4C->NGK B8S #3810<br />J4C->NGK B7S, NGK stock #3710<br />J4C->NGK BM7A #6521 might be obsolete part #<br />J8C->NGK B6S #3510<br />J8C->NGK B4 #3210<br /><br />The resistor (R) type, which might be more desirable, is RJ8C which crosses to BR6S #3522. The ceramic part which the wire boot goes over will be longer. If it fits under the cowl, then it'll work.<br /><br />FYI, American plugs such as Champion, Autolite, have colder heat range as spark plug part number decreases. J4C is colder than J8C. Japanese plugs are opposite, B8S is colder than B7S. The most important things are plug reach & heat range. Reach too long will hit piston and wreck engine, too short won't ignite fuel properly. heat range too hot will melt plug, cause pre-ignition & engine damage. Too cold will cause plug fouling, poor fuel economy and loss of power. Trick is to find heat range where plugs burn hot enough to stay clean but not too hot to cause pre-ignition or spark plug damage. Most marine engine/outboards spec a colder spark plug because the engine is loaded more and there's more combustion chamber heat. But if the J4C after running hard still has a wet look, then consider a J6C or J8C or cross ref. equivalent. Bosch, autolite, denso, are all in the cross ref. matrix.

 

[phatmanmike]

Re: Anyone have spark plug cross reference?

nice post.<br /><br />possible canidate for FAQ ????<br /><br />wheres jb when you need 'im

 

[seahorse5]

Re: Anyone have spark plug cross reference?

Be advised the Johnson and Evinrude do not subscribe to the "cross-over" charts. <br /><br />The only factory approved sparkplug chart is published each year in the Genuine Parts and Accessory Catalog. Most OMC CD ignition systems require a suppressor style of plug, also called and inductive resistor. It is completely different from a regular resistor plug.<br /><br /> http://www.championsparkplugs.com/sparkplug411.asp?kw=CDI&mfid=2

 

[Crossflow235]

Re: Anyone have spark plug cross reference?

I have had better luck with the Bosch Plantium WR9FP in my crossflow 235. Of course the factory recommended plug works OK. If you use anything but the factory recommended plugs you need to read your plugs, jet properly for altitude, prop correctly, and use proper octane.<br /><br />The factory is conservative because they are trying to cover the worst situation possible. The person who just adds oil, gas, and runs it. Thus the colder plug range. A hotter plug will give you better idle, take off and some minor gains in fuel economy. Higher BTU's = higher HP (to a point) The down side... possible meltdown if you don't do the following items mentioned above.<br /><br />I have tried the recommended champion plugs in my motor (standard and premium) and performance on idle and take off were very poor. Plugs were always fouling out or cylinders not firing to full capacity.<br /><br />I use my boat for skiing as well as high speed crusies and have tried several brands and have had the best luck with Bosch.<br />Interesting point also they cost less...<br /><br />Just food for thought...

 

[walleyehed]

Re: Anyone have spark plug cross reference?

The heat-range of a plug is simply how/rate in which it transfers heat.<br />Use only the correct Champion plugs in the JohnRude products....the ignition systems are designed around champion plugs.

 

[ron7000]

Re: Anyone have spark plug cross reference?

http://www.ngk.com/sparkplug411.asp <br /><br />bottom left of page is their numbering system,<br />and should make you CDI guys happy <br /><br /> http://www.ngk.com/ <br />also has a part finder via application, including outboard marine.<br />I believe their excel spreadsheet is everything though, and is bestto refer to for verifying a cross reference has all the same dimensions as the original plug.<br />But it's up to you of course to know the correct type plug for your application, that it won't necessarily help you with.<br />Happy X-reffing.<br /><br />... it looks like the ngk and champion info pages are links to www.sparkplugs.com<br />which is definitely a good read

 

[ezeke]

Re: Anyone have spark plug cross reference?

You might find this chart as helpful as I have. Champion Spark Plug Chart