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How much difference will wrong spark plugs make?

Discussion in 'Technical and Troubleshooting Torque' started by Burnsie, Apr 28, 2006.

  1. I have been having trouble getting the spada to start lately- it has been running well, but when the weather got colder, it began to not start easily, then wouldn't start at all.

    Checked the plugs- could get a spark from one, but not the other, so thought I may as well see if two new ones make a difference. As I haven't had it that long I checked what type they should be: cr8eh-9 it what says everywhere I looked, but the plugs were cr9eh-9's.

    My question is: How much difference will that make? It had been runnning really well for the last 500k's or so, then seemed to give up on the whole starting thing.

    Have to say, though, it IS running really well now that I've put the right plugs in, and seems to be much happier now.
  2. Plugs are designed for the application of the bike. For instance if you are racing you put a plug in that ignites hotter and can withstand higher temperatures, prevents things like pinging etc. If you put these plugs in and are not racing it can ultimtely lead to things like engine seizure etc
  3. Also the weather has a little bit to do with it... You can set up the bike for running in colder weather by using different plugs (though here in OZ it does not get that cold)...

    Also does any ome know... in cold clymate should you use a hotter or cooler plug??
  4. I hope this helps some of you and don't get too technical , oh and a little trivia at the end.

    But I'd be checking your battery, cold weather can show up a bad battery real fast, and seeing as you say you have changed the plugs with not much success the problem must be elsewhere, could even be the coil pack starting to give out ????????????
    But as for your question about the plugs, one level higher of lower wont affect the bike much at all. ( the recomended one is best but if you cant get them ) a different range will do. Also most bike shops will have a reference book where they can look up the different brands of plug to match the one your after .... NGK/CHAMPION etc etc

    The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber but not vice versa. If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shorting-out of the spark current.

    A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug. A spark plug is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug. The heat range of a spark plug is typically specified as a number, with some manufacturers using ascending numbers for hotter plugs and others doing the opposite, using descending numbers for hotter plugs.

    The heat range of a spark plug (i.e. in scientific terms its thermal conductivity characteristics) is affected by the construction of the spark plug: the types of materials used, the length of insulator and the surface area of the plug exposed within the combustion chamber. For normal use, the selection of a spark plug heat range is a balance between keeping the tip hot enough at idle to prevent fouling and cold enough at maximum power to prevent pre-ignition leading to engine knocking. By examining "hotter" and "cooler" spark plugs of the same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have more substantial ceramic insulators filling the gap between the center electrode and the shell, effectively carrying off the heat, while the hotter plugs have less ceramic material, so that the tip is more isolated from the body of the plug and retains heat better.

    Heat from the combustion chamber escapes through the exhaust gases, the side walls of the cylinder and the spark plug itself. The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature. A cold plug will not materially cool down an engine's running temperature. (Too hot of a plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature.) Rather, the main effect of a "hot" or "cold" plug is to affect the temperature of the tip of the spark plug.

    It was common before the modern era of computerized fuel injection to specify at least a couple of different heat ranges for plugs for an automobile engine; a hotter plug for cars which were mostly driven mildly around the city, and a colder plug for sustained high speed highway use. This practice has, however, largely become obsolete now that car's fuel/air mixtures and cylinder temperatures are maintained within a narrow range, for purposes of limiting emissions. Racing engines, however, still benefit from picking a proper plug heat range. Very old racing engines will sometimes have two sets of plugs, one just for starting and another to be installed once the engine is warmed up, for actually driving the car.
  5. Yeah... wot he said :p

    In the case of one number difference (cr9eh-9 or cr8eh-9) It'll make stuff all diference, esp at starting.

    What is more important in your case is wether it uses a "resistor" type plug or not. If the ignition is built for a "cr" plug, don't use non resistor type plugs and visa versa (IIRC the CR part of the code means resistor, but I might be wrong)

    I'd first check that the plugs are OK (clean, right gap), and has a good spark (remove plugs, replace leads, earth plugs AWAY from spark plug 'ole, crank engine and check for a nice fat spark, you should even be able to hear it.)

    If that was OK, then the next step would be fuel, or timing or even valve clearances. But as you've changed plugs and it's OK, well... it must have been dirty or too much gap on the old plugs maybe, too big a gap will certainly make starting harder.

  6. Thanks for the info guys.

    They were definately the wrong plugs- putting new ones in fixed the problem straight away, so I'm hoping that's all it was. The only problem was starting- not that I could get it started to say it ran OK, but it seems to be all fixed now.
    Will just have to wait and see.