Can someone tell me te differance between spark plugs and the numbers. Also Why is the gap so importart? I had a 8HS (I think) but put a 7HS in and the bike ran better? Is the standad gap not good enough. I just put the plug in the bike and away I go.. Reading a few posts here this doesnt seem like the right thing to do? Wise words would be good so I can understand better.

Jenny, June 2010

Sorry but ME is wrong (above with his/her answer)on one account above as a cooler engine uses a higher number plug not vice versa contrary to popular belief.
so a b8hs for instance is used in a cool running engine and a b4hs would be used in a hot running engine
yep you would have had a b8hs and put a b7hs in it.
i know a few of the codes off the top of my head
p. means pretruding electrode
b means its a 14mm plug thread ( i think)
r means the plug has a resistor in the ceramic part that stop radio interference
c at the beginning means its a 16mm hex
i means its an iridium electrode
g means its a grooved electrode
to save me listing all the meanings i just googled it and found this link :)
http://www.spark-plugs.co.uk/pages/technical/ngk_symbol_code.htm

adam bike doctor, June 2010

Thanks M and Me... I didnt realise!

I will take your words and buy a feeler gauge!

Jenny, June 2010

the numbers on the plugs relate to the heat rating of the plug. the 8 would be a plug to put in a hotter running engine rather than a 7. you should put in the plug the manufactuer reccomends for optimum performance. the gap is important as too big a gap results in a weak spark and to small a gap also a weak spark as spark wont jump a small air gap. again man spec should be followed.

me, June 2010

plug gap is extremely important especially if you want bike to run properley, the numbers on the plug are what define wether you put a hole in your piston or not, and ulimately wreck your engine, the actual number on the plug is the heat range and this is very important, the other numbers define thread length etc
Always check that the spark plug gap is compatible with the engine manufacturers specification. A gap that is too small means that the spark duration will be very quick and the spark will be thin and weak. The consequences of this may be bad starting and high exhaust emission levels. This will result in an increase in fuel consumption. If the gap is set too large, the ignition system will not be able to cope with the demands and a misfire situation will occur. Some wide gap spark plugs have a longer ground electrode to accommodate a wide gap setting. These must be used where specified, as opening up a standard plug to a wider gap setting may result in the electrodes not running parallel to each other. This could result in abnormal and premature electrode wear.

m, June 2010