Enlighten me about spark plugs

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    thepetrolist


    Replies: 43
    Topics: 20
    #1413

    Hi guys

    Spark plugs have always been kind of a mystery for me. So simple yet so hard to understand. I guess many of you feel the same way about something really simple.

    Anyway, today I got me some new spark plugs for a couple of my engines (’63 sportwin, ’60 JW16).

    When I got the engines, they both came with J6J plugs. The technical specifications recommended to use J4J’s, but I didn’t realize that until I had already bought them. I just bought the same plugs that were already in the engine. Well, they were Bosch W8ECs but they’re still the same.
    I installed the plugs and they both ran fine, so I decided to try some new plugs in my 1951 HD-26 since it too is running some really old J4J’s. Here comes the mystery part:
    The engine started just fine with the new plugs, then started to run rough, didn’t rev, and finally died. Then I just couldn’t get it running again! I tried and tried and tried, but no luck. I reinstalled the old J4J’s and it fired right up and run really well again.
    Note, new plugs were J6J spec plugs.

    Can anyone tell me why this happened? Is the J6J so much hotter than the J4J that it simply wouldn’t run on it?
    If so, why did the JW-16 run with those plugs but not the Hd-26? They are still pretty much the same engines.

    Note no. 2, nothing but the plugs was changed. I ran fresh gas with fresh oil.
    Oh, and I ran the exact same plugs in the JW as in the HD, I simply switched since I had bought too few (luckily).

    Seems I have to go back to the store to get som J4J spec plugs now.

    frankr
    frankr


    Replies: 5301
    Topics: 48
    #15373

    I seriously doubt the heat range (J4 vs J6) had anything to do with it. Something else is going on there. You mentioned Bosch. I am totally ignorant concerning Bosch numbers. They may not be exact interchanges. Maybe a resistor plug or a booster gap plug or something on that nature? Or I could be off base here. Also could be something as simple as different plug gap.

    Tubs
    Tubs

    US Member - 1 Year
    Replies: 3152
    Topics: 172
    #15375

    It’s the reason I search for
    NOS AC spark plugs.
    There must be other brands
    that are reliable but I have
    always had good luck with AC’s
    so as long as I can get them
    that what I’ll use.
    Try changing brands and see
    what happens. May be the reason
    it had Bosch plugs in it when you
    got it.

    You're only as smart as the person you're talking to.

    Avatar
    legendre


    Replies: 389
    Topics: 8
    #15377

    It’s possible that the hotter plug caused a slight overheating condition which resulted in vapor lock, stalling the engine. But otherwise, about the only way a too-hot plug stops an engine is by provoking a seizure or burning a hole through the piston. What did the new plugs look like, when you pulled them from the stalled motor?

    BTW – was this all done in a test tank, or out on the water? Sure, these are water-cooled motors, but they can get a lot hotter ‘under the hood’ when sitting in still air – and that’s where the vapor lock originates.

    Finally, for the most part, plug cross-references are general guides and some types / makes of plug just seem to work better in certain motors. As you might have noticed, NGK is my go-to plug – they’ve never done me wrong. And you should +never+ use any other plug (except for perhaps a Denso) in a Japanese motorcycle or car. However, the Denso u-groove plugs burn extremely well in the older Ford L6 motors, 240 cid, 300 cid.

    I’ve never had good luck with Bosch plugs, except in BMW motorcycles and one particular moped. Champion are OK for lawn mowers, snow blowers, outboards / power equipment and.. Harleys. Otherwise, I avoid them like the plague for motorcycles or cars.

    When NGKs are two bucks, and widely available, I just can’t think of any reason to mess with anything else, really. Maybe try a pair of B7S some time.. or B6S if you want a little hotter, B8S for a little cooler.

    Avatar
    pappy

    US Member - 2 Years
    Replies: 616
    Topics: 37
    #15378
    quote legendre:

    It’s possible that the hotter plug caused a slight overheating condition which resulted in vapor lock, stalling the engine.

    Talk about the need for enlightenment…….!!

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    retiredoz

    US Member - 1 Year
    Replies: 487
    Topics: 47
    #15384

    Did you put the plugs that failed in the HD-26 back into the JW ? Just curious.

    Avatar
    thepetrolist


    Replies: 43
    Topics: 20
    #15385
    quote Pappy:

    quote legendre:

    It’s possible that the hotter plug caused a slight overheating condition which resulted in vapor lock, stalling the engine.

    Talk about the need for enlightenment…….!!

    Yeah, well, I guess you’ve never been a newbie and never made mistakes?
    And sometimes ones brain farts and can not for the love of something figure out whats wrong.

    Avatar
    thepetrolist


    Replies: 43
    Topics: 20
    #15386
    quote retiredoz:

    Did you put the plugs that failed in the HD-26 back into the JW ? Just curious.

    Of course not.

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    Randy in Tampa


    Replies: 708
    Topics: 117
    #15391

    Try autoliite 303’s i’ve had good luck with them 😉

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    chinewalker

    US Member - 2 Years
    Replies: 459
    Topics: 17
    #15395

    I have found that a great deal of the "this brand of plug works better than that brand" stuff is more to do with set-up of the ignition, quality of the fuel, and quality of compression. I have never seen a motor issue that could be directly attributed to plug "brand". I have seen many that were blamed on plugs that were actually related to poor quality fuel, incorrectly adjusted carburetor, poorly maintained ignition, low compression, leaky gaskets, etc. If your compression is good, fuel is clean and fresh, and your spark is hot, it’ll run on the recommended plug, no matter the brand.

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    retiredoz

    US Member - 1 Year
    Replies: 487
    Topics: 47
    #15400

    Well, give it a shot and see what happens ? At least, thats what I’d do…

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    chris-p

    Canada Member - 1 Year
    Replies: 2484
    Topics: 157
    #15403

    Yeah I know a lot of guys poop on Champions for some reason, but NGK is not some magical plug. I buy the J6s and J4s by the hundred box and can only think of one problem Ive had. Not against running other brands either, if I have them.

    Avatar
    legendre


    Replies: 389
    Topics: 8
    #15405
    quote thepetrolist:

    quote Pappy:

    quote legendre:

    It’s possible that the hotter plug caused a slight overheating condition which resulted in vapor lock, stalling the engine.

    Talk about the need for enlightenment…….!!

    Yeah, well, I guess you’ve never been a newbie and never made mistakes?
    And sometimes ones brain farts and can not for the love of something figure out whats wrong.

    I’m only a ‘newb’ as pertains to OBMs – my experience is very limited in the area. That said, I have more than a dozen or so years working in and managing motorbike service shops, and decades playing with my own toys – so if anything, I’m more qualified as an old fool. 😉

    Back on point..

    Spark plug heat range controls more than just the temperature at the spark plug’s tip. It also has an effect on the peak temperature of the combustion chamber, and more importantly – the flow of waste heat through and out of the motor.

    Colder plugs run cooler, by virtue of being more efficient at passing chamber heat into the cylinder head and then to atmosphere via the cooling fins or water jacket. Hotter plugs not only run hotter at the tip but also are less efficient in conducting heat away to the head & atmosphere – but the engine still has to get rid of that heat some way.

    One way it does this, is by releasing more of the heat in the exhaust gas.. which increases exhaust manifold temperatures. In an outboard design where the exhaust manifold is closely-coupled to (sometimes even an integral part of) the intake system, this can lead to higher temperatures in the intake, carb and fuel lines, particularly if the lines are copper.

    Anyway, I’m not sure what folks are objecting to.. so far, I’m the only one to have stuck-out their neck and posited a hypothesis as to why plug heat range alone might have stalled the OP’s motor. Feel free to knock it down, that’s fine, but it would be helpful if you also offered a competing hypothesis..

    -L

    Avatar
    thepetrolist


    Replies: 43
    Topics: 20
    #15433

    Ah, I see!
    Thanks for the clarification.

    Today I once again bought some new plugs. Luckily I work at an auto supply store so I can check up on plugs while at work. 😀
    We were out of NGK B7S and Champion J4C’s but I got Denso W22S-U:s . They matched the specs so I thought I’d give it a shot. Installed them, pulled the starter.. And off they went! Ran better than ever before, both the HD and the Sportwin. Which brings me back to the thought about the Bosch W8EC plugs being dodgy. But what is the chance that FOUR brand new plugs are bad?
    Any other thoughts?

    Just for the heck of it I also got a denso M17 for my ’67 Seagull and that too ran much better than before.. But that engine ran a 40 year old Bosch M45 so no wonder..

    Avatar
    pappy

    US Member - 2 Years
    Replies: 616
    Topics: 37
    #15437

    Let me simplify this for you although with a simple Google search you could have avoided printing the mis-information yourself.
    http://matchlessclueless.com/mechanical … mperature/

    Secondly, give us an example on an outboard where the intake is closely couple to or an integral part of the exhaust. Most I have seen have the intake on one side of the cylinder and the exhaust on the other.

    The point here is that folks are here to learn FACTS about their outboards. If you know something as FACT, fine, post away. If not, bear in mind that you are possibly misleading those who are here to learn and worse yet, cost someone money and time following that misinformation.

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