Spark plug question

[spunkyjr]

The motor is 9.9 1964 model and it had J6C plugs in it. I wanted to change the plugs before the cold weather sets in. Looked in iboats and it list a j8c as the plug for this model year. Which one is right? Could the plugs be inter- changed and what effect would it have on the motor?

 

[F_R]

Re: Spark plug question

The motor is 9.9 1964 model and it had J6C plugs in it. I wanted to change the plugs before the cold weather sets in. Looked in iboats and it list a j8c as the plug for this model year. Which one is right? Could the plugs be inter- changed and what effect would it have on the motor?

That is just plain wrong. It is supposed to have J4J (C). Seems like they don't want to make them any more so they say J6C which is a heat range hotter. Now they are saying J8C--another step hotter. I will accept J6 but not J8. It isn't iboats, it's Champion. They seem to be the attitude that if it fits the hole use it.

 

[Vic.S]

Re: Spark plug question

9.9 and 1964 ?? do you mean 9.5 or is the year wrong.

For a 1964 9.5 the currently recommended plug is J4C (gapped at 0.030")

Still listed as available from Sparkplugs.com

Equivalents are Autolite 353, Bosch W5EC, Denso W24S-U, NGK B7S (or B8S*)

However equivalents may not be exactly the same heat rating

*Note NGK B8S is cooler than B7S.

If I could not obtain the J4C s I'd have no qualms about using NGK B7S.

The NGK equivalent of J6C is B6S (The hotter plugs, J6C or B6S, would be useful perhaps if you are using the engine a lot at trolling speeds rather than WOT and fouling becomes a problem)

 

[F_R]

Re: Spark plug question

9.9 and 1964 ?? do you mean 9.5 or is the year wrong.

For a 1964 9.5 the currently recommended plug is J4C (gapped at 0.030")

Still listed as available from Sparkplugs.com

Equivalents are Autolite 353, Bosch W5EC, Denso W24S-U, NGK B7S (or B8S*)

However equivalents may not be exactly the same heat rating

*Note NGK B8S is cooler than B7S.

If I could not obtain the J4C s I'd have no qualms about using NGK B7S.

The NGK equivalent of J6C is B6S (The hotter plugs, J6C or B6S, would be useful perhaps if you are using the engine a lot at trolling speeds rather than WOT and fouling becomes a problem)

Thanks Vic, I didn't catch the discrepancy. My reply was based on the assumption that it is a 9.5. The AC equivalent for J4J is M42K. I still have a bunch of NOS AC's

 

[spunkyjr]

Re: Spark plug question

Sorry yes it is a 9.5 just hit the wrong key.

 

[14ftgrumman]

Re: Spark plug question

a few years back, Champion re-aligned the heat ranges of thier offerings. A J4c of 30 years ago may very well be called a J6c or a J8c today.

After he change to heat ranges, I installed a new set of J4c in my 59 18HP. Were the "new" designation J4c. Were too cold, fouled out and left me stranded in the middle of Shawano Lake.

I've sold car parts for 30+ years. Been to all the seminars. Engines are stupid. They do not know what brand of spark plug is screwed into them. If the heat range is correct, it will perform. DO NOT go by interchange lists. Use the catalog. An interchange is someones best guess.