Page 1 of 3 123 LastLast
Results 1 to 10 of 22
  1. #1
    Computer "Specialist" Agent_24's Avatar
    Join Date
    Dec 2004
    Location
    64 Bitville
    Posts
    14,381

    Default Spark plug madness - what's the answer?

    I recently bought a very cheap Ryobi line trimmer (Quickcut slasher) second hand as not working. It's a model RST31E with a 31cc 2-stroke engine.
    The spark-plug was dirty and cleaning it got the engine going, but I decided to just get a new spark-plug (have had the same problem with my lawnmower in the past).

    The plug that was in there is an NGK BPM6F. A spare-parts website (https://www.toolspareparts.com.au/ry...are-parts.html) claims the correct plug is an NGK BM6F (which is the same thing, but of recessed electrode design).

    However, after acquiring a PDF copy of the user manual from Ryobi, it tells me different again: use a Champion RDJ7Y or equivalent. This is apparently the same as the NGK BPMR6F - R meaning added series resistor, in addition to having a "normal" projected electrode.

    Now I had gone to Mitre10 and bought a Champion DJ8J believing that the BM6F was correct, but now I am unsure if I should actually use it. NGK state:
    "Use of non-resistor plugs in vehicles that call for a resistor type can result in rough idling, high-rpm misfire, and abnormal combustion."
    as well as:
    Retracted or recessed center electrodes are designed to place the spark out of the mainstream air/fuel flow. This makes it difficult to initiate a good flame front, but is necessary when valve or piston clearance is insufficient for conventional plugs, or when boost pressures and/or fuel type can cause excessive combustion chamber temperatures.
    To me, it sounds like the plug I bought would be the worst choice as it is both unnecessarily recessed, and does not have the series resistor.

    But perhaps I am overthinking it. Do such things matter for small engines in garden tools? Shall I take the trouble to go and get the correct BPMR6F from Repco?
    Would there be any good reason (other than cost, ease of availability, or carelessness) that a non-resistor plug was in there at all?
    Non-system disk or disk error. Replace and strike any key when ready.

  2. #2

    Default Re: Spark plug madness - what's the answer?

    Buy a very expensive one. Kidding aside, I would always go for quality man.

  3. #3
    Computer "Specialist" Agent_24's Avatar
    Join Date
    Dec 2004
    Location
    64 Bitville
    Posts
    14,381

    Default Re: Spark plug madness - what's the answer?

    Quote Originally Posted by ChooseParis View Post
    Buy a very expensive one. Kidding aside, I would always go for quality man.
    Quality is not really the question here, both Champion and NGK are well known, respectable brands, and I certainly wouldn't advocate for the use of generic copies that probably fall to bits or rust solid.

    I'm more interested to know how much the differences between variants of the same spark plug actually matter in this scenario.

    Of course, I can easily go and buy the plug recommended in the user manual, and most probably will do so, as that is a more trustworthy source than a random website with no evidence to back up their claim, but blindly doing that does not wholly satisfy me.

    I am intrigued; is the result of using the 'wrong' plug variant nothing worse than potential loss of performance, or can actual damage occur?

    Obviously a too-long plug impacting against the piston is an easy to understand result, but I wonder about more subtle issues, for example; if mixing up resistor vs non-resistor spark plugs is likely to damage the ignition system, or if someone might have deliberately installed one or the other for good reason (e.g. Improve performance in a worn engine, compensate for badly adjusted carburetor, etc etc, I don't know, just making semi-educated guesses).

    Is there anyone here with the experience/knowledge to know the answers?
    Non-system disk or disk error. Replace and strike any key when ready.

  4. #4
    Old guy
    Join Date
    Dec 2004
    Posts
    2,960

    Default Re: Spark plug madness - what's the answer?

    You are over thinking it all. I would use the makers recomended one or its equivilent. At a guess the wrong one was used because that is what the last owner had to hand.

  5. #5
    Senior Member piroska's Avatar
    Join Date
    Dec 2017
    Location
    With Kim-Jong-Mum
    Posts
    3,557

    Default Re: Spark plug madness - what's the answer?

    Quote Originally Posted by Agent_24 View Post
    I recently bought a very cheap Ryobi line trimmer


    But perhaps I am overthinking it. Do such things matter for small engines in garden tools?
    Ask your local repair guy. I find they (well the good ones) know what matters and what doesn't, and often have parts cheaper than Repco or the like.
    Ex-pctek

  6. #6
    Senior Member 1101's Avatar
    Join Date
    Jan 2008
    Posts
    7,435

    Default Re: Spark plug madness - what's the answer?

    Its a cheap, one of purchase.
    Just go and buy EXACTLY what the manufacturer recommends .

    The other plugs will probably work in the short term . That doesnt make them the best choice though .

  7. #7
    VoidMaster
    Join Date
    Dec 2004
    Posts
    6,513

    Default Re: Spark plug madness - what's the answer?

    My understanding is that the resistor is there for spark suppression of radio interference. As a motor wears and oils up the spark plug a bigger spark is useful to start the motor hence taking the resistor spark plug out and replacing it with what you have.

    However the answer to all these problems is CRC Engine Start, expensive at $25 a spray can, lasts for hundreds of starts, worth every penny, so to speak.

    Squirt into the airfilter and away you go, no matter how oiled up the plug is.

    Please give feedback on whether this works well for you or not.

    Once upon a time spark plugs were cheap at $1-50 but now at $5-00 not a thing to replace often.

    A wire brush and wipe with an old towel works wonders on an old oiled up spark plug and as a last resort spray Engine Start into the spark plug mounting hole before putting the plug back in.
    Last edited by zqwerty; 26-05-2021 at 09:52 AM.
    It's not the least charm of a theory that it is refutable. The hundred-times-refuted theory of "free will" owes its persistence to this charm alone; some one is always appearing who feels himself strong enough to refute it - Friedrich Nietzsche

  8. #8
    Its ok I am from Motueka. prefect's Avatar
    Join Date
    Aug 2008
    Posts
    9,046

    Default Re: Spark plug madness - what's the answer?

    I work as a mechanic at hirepool as a retirement job and work with and curse small engines all day long. Worked there a few years now and I could count the number of properly dead spark plugs on one hand. We dont mess around when an engine wont start we throw in a brand newie or from a box of used known goodies and put the suspect sparkplug in an ice cream container. When's its over flowing we find an engine that starts well and runs well and recycle the sus plugs through it after visually checking the gap (dont use gay setting tool) wirebrush blast with brake kleen blow with air gun. Normally the whole container will work fine. Basically only 3 plugs the BPMR7A for all two strokes and others for Robin or Honda. The reason you should get the right plug is if the plug is too long when you pull it the tip will hit the piston never a good thing Resistor plugs are just for radio interference and the non resistor plugs will always work better, its not rocket science you just have coil that gets passed by a magnet on the flywheel sending a spark down the plug lead you put in a resistor you kill some of the spark. The biggest problem here are liars who dream up stuff like resistor plugs are matched with coil windings fake news and dumb fukks believe it.
    The trick with engines is to read the spark plug when the engine wont start is wet, is it oily, is carboned, up is it dry as a nuns? and go from there.
    So fit any plug that converts over from the manufacturers OEM plug: NGK Champion Commie Chinese ones any furkin plug there is no such thing in NZ as a bad plug. A two stroke can easily get flooded and the plug wet as that song by Cardi B. Got to get rid of the excess fuel in the crankcase. Trick dump the gas on the concrete out of the tank, throttle full open and pull like a school boy, does not start remove and dry the plug till it does of course you are checking after you have dried the plug it is sparking.
    This depends on the fact you have compression test by holding engine from starter and it should hold its own weight. You are pissing into the wind if the carb is rooted or the crank seals are buggered.
    As someone said if the plugs is dry as a nuns spray some ether into the carb and if it goes you know you have a gas problem start with the filter in the tank hook it out with a wire and clean it before you go down the carb kit path. Of course you would have mixed gas no older than 3 months,
    Its amazing how Potatoes give us chips,fries and Vodka.

    Get your s*** together every other vegetable.

  9. #9
    Retired old codger kenj's Avatar
    Join Date
    Nov 2006
    Location
    Nhapier
    Posts
    5,813

    Default Re: Spark plug madness - what's the answer?

    Quote Originally Posted by zqwerty View Post

    However the answer to all these problems is CRC Engine Start, expensive at $25 a spray can, lasts for hundreds of starts, worth every penny, so to speak.

    Squirt into the airfilter and away you go, no matter how oiled up the plug is.

    Please give feedback on whether this works well for you or not.
    Guy down the road had an old 3 wheel Morgan and he used that grand old Aussie product "Start Ya Bastard"

    I assume that's similar?

    Ken
    Corgi Ben Kenobi.......Related by Corgi to the Queen

  10. #10
    Computer "Specialist" Agent_24's Avatar
    Join Date
    Dec 2004
    Location
    64 Bitville
    Posts
    14,381

    Default Re: Spark plug madness - what's the answer?

    Thanks everyone for the replies and advice.

    I returned the DJ8J to Mitre10 and bought an BPMR6F from Repco instead. At $9.89 it wasn't too bad for a trimmer that only cost $6.
    After setting the gap (0.5mm) as per the manual, I installed it and the engine started very easily and ran much smoother than with the old, but cleaned, plug. It was also able to idle without immediately dying.

    I trimmed everything that needed trimming, which finished off what line was left in the spool, with only minor issues. The engine stalled 3 times - once due to becoming entangled in thick Kikuyu grass. Twice after idling while taking a short walk across the lawn, although at other times it idled for longer without problem.

    The previous owner had replaced the primer bulb and a fuel line (said they were cracked).
    Perhaps the idle speed needs adjusting?


    Quote Originally Posted by prefect View Post
    The biggest problem here are liars who dream up stuff like resistor plugs are matched with coil windings fake news and dumb fukks believe it.
    I have no idea about that, but I have read that dirty plugs or plugs with a too-large gap need a higher voltage to fire and thus put more stress on the ignition coil, leading to premature failure. I was not sure if incorrectly using resistor/non-resistor plugs could do the same thing.

    Quote Originally Posted by prefect View Post
    The trick with engines is to read the spark plug when the engine wont start is wet, is it oily, is carboned, up is it dry as a nuns? and go from there.
    I am not a spark-plug expert. I've attached a photo of the plug that came with it.

    Quote Originally Posted by prefect View Post
    Of course you would have mixed gas no older than 3 months,
    It was a fresh mix done that day. When I bought it, the tank was empty and dry.


    Quote Originally Posted by CliveM View Post
    You are over thinking it all. I would use the makers recomended one or its equivilent. At a guess the wrong one was used because that is what the last owner had to hand.
    Most probably - but I like to explore other avenues too. It's all interesting.

    Quote Originally Posted by piroska View Post
    Ask your local repair guy. I find they (well the good ones) know what matters and what doesn't, and often have parts cheaper than Repco or the like.
    That's the question isn't it though - how do I know the local repair guy is any good anyway? I typically DIY as much as I can, don't frequent repair shops of any kind very often at all, and have no experience with who's good or bad. But I can say that the 99% positive ratings on NoCowboys seem to be a complete joke.

    Quote Originally Posted by 1101 View Post
    Its a cheap, one of purchase.
    Just go and buy EXACTLY what the manufacturer recommends .

    The other plugs will probably work in the short term . That doesnt make them the best choice though .
    I agree, the manufacturer usually recommends a certain part for a reason, but as pointed out below:

    Quote Originally Posted by zqwerty View Post
    My understanding is that the resistor is there for spark suppression of radio interference. As a motor wears and oils up the spark plug a bigger spark is useful to start the motor hence taking the resistor spark plug out and replacing it with what you have.

    However the answer to all these problems is CRC Engine Start, expensive at $25 a spray can, lasts for hundreds of starts, worth every penny, so to speak.
    Please give feedback on whether this works well for you or not.

    Once upon a time spark plugs were cheap at $1-50 but now at $5-00 not a thing to replace often.
    Indeed, I have noticed examples where older things may require changes from factory to restore performance etc. Increasing the filament voltage in an aging CRT comes to mind. Re-bored cylinders needing larger piston rings etc. Removing the resistor plug to get a bigger spark for an older engine sounds like a logical concept.

    I can't tell you how the spray starter worked as I didn't try it. Since the engine did start (although a bit rough) with the old, but cleaned, spark plug, I figured a new one would do it good. If it fails again in short order I may consider the starter fluid, if no other problem is obvious.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	IMG_20210530_1020593.jpg 
Views:	26 
Size:	33.8 KB 
ID:	10925  
    Non-system disk or disk error. Replace and strike any key when ready.

Similar Threads

  1. Google madness
    By headshot in forum PressF1
    Replies: 5
    Last Post: 26-08-2011, 04:37 PM
  2. Madness...
    By somebody in forum PC World Chat
    Replies: 23
    Last Post: 11-06-2007, 07:59 AM
  3. midtown madness 2
    By in forum PressF1
    Replies: 3
    Last Post: 20-06-2002, 11:05 PM
  4. midtown madness 2
    By in forum PressF1
    Replies: 3
    Last Post: 19-06-2002, 08:41 PM
  5. midtown madness 2
    By in forum PressF1
    Replies: 1
    Last Post: 19-06-2002, 04:27 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •