Will running a hotter plug hurt my engine??

[mrbigal81]

i have a 89 cr500 that i beleive takes a BR8EG plug stock. i put a BR9EG in it now. will this hurt anything? I was having problems starting the bike so i have been running the hotter plug and it seems to help.would it help even more to but a 10 in there? :think

 

[fmfkx125372]

mrbig,

The 9 is actually colder than the 8. Running a hotter plug won't really hurt the engine unless you are already running on the lean side. If the 9 seems to be working, I would leave it alone...

 

[mrbigal81]

really.. i guess my old plug was just shot.

 

[Lutz]

As I was typing others replied...so here's my reply anyway.

If I'm not mistaken, by NGK's code system, the larger the number, the colder the heat range of the plug. Thus a BR9EG actually has a colder heat range than the BR8EG.

However, the heat range of the plug has nothing to do with the heat of the spark; the heat range mainly has to do with how fast the center electrode can cool. A plug with a hotter heat range (lower NGK numbers) retains more heat, so it can burn off deposits better, and therefore resists fouling. However, in the wrong conditions a plug with a hotter heat range can retain too much heat, and cause detonation or actually melt the electrode. On the other hand, a plug with a colder heat range (higher NGK numbers) doesn't retain as much heat, and is therefore more prone to fouling because it can't burn off deposits as easily; but it is less likely to cause detonation or melt.

Generally, a plug with a hotter heat range is needed if you have problems with plug fouling at low speeds (as when you lug the engine for long periods of time). A colder heat range is necessary if your plug is overheating and/or causing detonation (as when you ride at high speeds with the engine revved up). There are other factors involved here (ignition timing, jetting, etc.) but strictly with respect to plugs, that is the basics.

So...changing the heat range of the plug shouldn't have anything to do with how easy a bike is to start. If changing the plug actually did make the bike start better, it is probably because the old plug was fouled or worn out. A bike with a new, clean, and properly gapped plug will always start better than one with a fouled/worn out plug. If the hard starting was due to a fouled plug, it is more likely that running the 9 as opposed to the 8 will make your starting problems worse over time, as the 9 will be more likely to foul. And so on with the 10. If the hard starting was due to a worn out plug, it should have been replaced with the a stock plug. If you go a LONG time between plug changes, it is likely that the old one was just worn out. Did you try replacing the BR8EG with another BR8EG? If not, then it is likely that the 8 would have made just as big a difference as the 9 did. It is also possible that by thinking you had a plug with a hotter spark, you thought that the bike should start easier, and that made the bike easier to start.

Now, as to possibilities of damage...
Running a "colder" plug, as seems to be your case, shouldn't ever cause any problems other than the plug might foul more often. On the other hand a "hotter" plug could cause damage if it is not necessary.

I hope I helped you more than confused you. In short, if a new stock plug works well, use it.

 

[mrbigal81]

wow, thanks for the info. i think the old plug was just worn out. i will replace the 9 with the stock plug. Thanks again