Spark plugs?

[B0000M]

i went to spectrum a couple of weeks ago, to grab a spark plug.

ive always run BR9EV's in my CR, and my bike occaisonally gets a bit of detonation.

i asked the guy there for a 9, he seemed surprised, and asked if i ever get detonation, i said yea sometimes, he said i should be running a 8.

i havnt done any riding since, but i thought id confirm my suspicions online and i was right in that a 8 range ngk plug is a hotter plug than a 9 range.


from what ive just read, it would appear that running a hotter plug is going to make my problem worse.

do we have any experts here?

scott411?
reckless?

[CookMySock]

Champion use lower numbers for colder plugs, while NGK and Denso use higher numbers for colder heat ranges. (references)

So you have to figure out whether the larger number will allow the plug to run at a higher temperature or lower temperature. But yeah, a hotter plug will be more prone to detonation for sure.. but which way is hotter or colder depends on the manufacturer.

Steve

[Reckless]

I've always associated detonation more to ignition timing rather than plug temp. Although I would have guessed the hotter it is in there the more likelyhood of detonation. Now if I remember rightly your Cr should run a BR8 as standard so if you say its detonating sometimes on a colder BR9 its worth getting the dail guage out and having a check on the timing I reckon.

Here's a bit of a read for you to save me typing it.

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

you might find setting the timing to standard or a fraction of retard might be a good thing, make it smoother and give you a bit of over rev.
You might also find you can try the Br8 and its better. I could run either in my Cr and it didn't seem to matter much although with the 8 it seemed a bit perkier (could have been my imagination though LOL!!).

If your last piston change showed any detonation marking around the piston top I'd definatly have a bit of a squiz at the rotor & timing.

To save me a whole lot of typing I did a google I'm sure you understand this but it was good for me to have a bit of a refresh of what I read here

Anyway to my untrained unskilled knowledge level, detonation = timing advance?? Possibly only a fraction out in your case?

You notice I said "you might" alot as well LOL!!! Hope this helps!

PS Your compressin is standard isn't it as High compression can cause detonation as well! Mind you to solve this I'd retard the timing a tad or lower the compression so same thing in the end.

[scott411]

yeah, what reckless, said, i would think a hotter plug would make it worse, but i am not a expert at this things,

most 250 2t's run a NGK 8 range plug, so i would stick with that

[CookMySock]

detonation = timing advance??

Depends what caused it.

"Detonation" or "pre-ignition" is a widely bounced-around term, which doesn't mean much unless it is presented alongside some analysis. Detonation is the sudden and explosive burn that is associated with high combustion chamber temperatures. How that high temperature is arrived at is what needs to be examined.

If the ignition timing is too far advanced, the engine will "ping" occasionally, but usually won't enter full-blown detonation until it has been worked hard for some time, and combustion chamber temperatures have risen to such a point that the fuel/air cannot be admitted on an intake stroke without it either igniting during the inlet stroke, or igniting suddenly and uncontrollably during the compression stroke. Either way, there will be a large loss of power, and this is fully-developed detonation. Suffice to say, piston, ring, and bore damage have already occurred.

If for the above reason, or any reason, such as too-hot a plug, the spark plug electrode rises to such a high temperature, the same problem will occur. The result is identical.

If the mixture is run too lean, combustion chamber temperatures will rise also. Same result!

So there is a big difference between a little ping while goosing the throttle, and full-blown detonation - the former often but not always being tell-tale of the latter.

Steve

[B0000M]

well this is the odd thing. - its always had a 9 in it, and ive only replaced plugs when i do top end rebuilds. - eg i dont foul up plugs, they wear out.

the guy at spectrum seemed adamint that the 8 was the way to go and said it was a colder plug, but NGK's online plug code guide thing disagrees. its pretty fair to assume NGK know what theyre talking about when it comes to spark plugs.

NGK suggests going to a colder plug if detonation is occuring, but i dont think i should need to go 2 plugs colder than the factory spec of BR8.

what i think ill do at this stage is get another 9 in there. and try to figure out how to adjust the timing.

the other point worthy of note is my bike only sounds like it detonates for the first few hours after a top end rebuild. obviously due to the compression.

as i havnt owned it since new, i can only presume nothing has been altered to give it more compression. but in its current state my leg-o-meter tells me its got shitloads.


anyone know how to adjust the timing on a CR to save me having to figure it out for myself?

i presume there must be something i can turn slightly in behind the flywheel (dam shouldve looked when i had the flywheel off with the cases apart!)

[Reckless]

oh and B000m a little trick we used with the dial gauge is to get an old plug smash the porcelain and centre out braze a little bracket on whats left (ie only the steel bit and thread) to Attach the dial gauge straight to.
Then screw the the new plug bracket thingy you made into the head and mount the dial gauge to it. Nice and solid and you don't have to shag about with the magnetic stand etc. I used mine heaps of times so good to have around.

I just looked and the bracket isn't in my Dial gauge box to take a pic of for you but if you don't understand the above let me know and i"ll mock something up for you. Checking the timing is only a quick job so should be easy for you to suss out.

[Reckless]

I agree with what DB says and its all in the articles I put links to in my post.

B00m if your bike doesn't overheat easy on those big sandy hill climbs etc I think its resonably safe to assume its not got altered compression. Bearing in mind I''ve ridden with you in the past and know your running 40:1 and everything seems pretty standard with your bike.
BTW my CR never fouled a BR8 or the colder BR9 at anytime either.

The only other thing I can think of is your running really lean causing it to run hot and detonate how does your plug look after a good blast, not white or light grey/white???

Timing is easy I'll explain after you have replied.

[Danger]

I think if Boom had bothered to take any notice of my past posts on the CR250 he will have already seen that I recommend an 8 series plug and retarding the timing slightly on this bike, but how many times can you repeat yourself before it gets through?

To retard the timing loosen off the stator and turn it a penny width or an 1/8" in the direction of the motor rotation, takes about 5mins.

[camchain]

Stop starting interesting threads, I'm not getting any work done.

[chop]

Honda recomend and sell the cr250 with a 9. bit odd but i wonder if this was to try and cure detonation in the first place

[Assasin]

I think if Boom had bothered to take any notice of my past posts on the CR250 he will have already seen that I recommend an 8 series plug and retarding the timing slightly on this bike, but how many times can you repeat yourself before it gets through?

To retard the timing loosen off the stator and turn it a penny width or an 1/8" in the direction of the motor rotation, takes about 5mins.

Why do you come across as such a knob? the guy was only asking a question surprised no one has knocked you out at a trail ride the way you talk to people. Internet or not you have to remember we all bump into one another eventually.

The way you talk you would swear you are KB king u are not.

Ban me I dont care it had to be said.

[B0000M]

dangee - yea ill have a play with the timing later on. the reason ive never done anything is it only makes the noise rarely

reckless - plug colour sits at a 1970s trend brown colour.

chop - quite likely

ill also go back to a 9. no sence in running it hotter than it needs to be

[Reckless]

Stop starting interesting threads, I'm not getting any work done.

Tell me about it between being sore from Wires track and KB my weeks been shite!!!!

[Danger]

Why do you come across as such a knob? the guy was only asking a question surprised no one has knocked you out at a trail ride the way you talk to people. Internet or not you have to remember we all bump into one another eventually.

The way you talk you would swear you are KB king u are not.

Ban me I dont care it had to be said.

Dude settle down, I come across as dry but I'm sure Booom can take it, we know each other and I know he has followed previous threads where I have offered advice on this bike. Our first post to each other was giving each other shit about riding sand whoops but when we meet on the trails its a handshake and a gidday. And Booom himself is quite dry without unnecessary pleasantries in my dealings with him but its all good, we understand each other. I'm the same with Cheese when he keeps asking about his jetting on his bike, but Cheese and I get on fine as well. Don't take me or life so seriously.