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Dang it! Toasted my top end....

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i just rebuilt my top end in my 03 rm125 two rides ago. today at the track i was riding it pretty hard, then swoosh, engine dies, no compression. at the track i pulled the sparkplug and see the electrode is gone. so i assume its been playing rattle can in the cylinder.

i went home and pulled the head. sure enough everything in there is scored.

so i pulled the motor. gotta find a box and pack it up. i'll ship it to Eric Gorr on monday.

can you say 144??? woot, woot.

so do i go for the mid to top, mo' everywhere, or bottom to mid porting? for track use only...

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i just rebuilt my top end in my 03 rm125 two rides ago. today at the track i was riding it pretty hard, then swoosh, engine dies, no compression. at the track i pulled the sparkplug and see the electrode is gone. so i assume its been playing rattle can in the cylinder.

i went home and pulled the head. sure enough everything in there is scored.

so i pulled the motor. gotta find a box and pack it up. i'll ship it to Eric Gorr on monday.

can you say 144??? woot, woot.

so do i go for the mid to top, mo' everywhere, or bottom to mid porting? for track use only...

I guess you did somthing wrong. Do you know why she blew?

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i pulled the sparkplug and see the electrode is gone. so i assume its been playing rattle can in the cylinder.

i went home and pulled the head. sure enough everything in there is scored.

Guessing the sparkplug may have had something to do with it!!!!!!!!!!

oem plug, in there too long. though it looked real clean and fresh when i checked it yesterday...

I had been contemplating going to an EG instead of an ES plug, I think you have just made my decision

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Guessing the sparkplug may have had something to do with it!!!!!!!!!!

I had been contemplating going to an EG instead of an ES plug, I think you have just made my decision

So the plugs are two different sizes?

I guaranty there is no difference in size between an ES and an EG.

If your electrode was fryed there is another reason.

More than likely it was super lean and your piston shatterd and ate your plug electrode.

Edited by mxn4life

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I would think this problem goes much deeper than a spark plug. Post a pic of the plug.

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Here is what the numbers mean on a plug.

B= 14 mm thread diameter

R= Resistor Plug

9= heat range

E= 19 mm thread reach

S= Racing plug

The most serious result of selecting a heat range that is too hot is overheating. Overheating will cause the electrodes to wear quickly and can lead to pre-ignition. Pre-ignition occurs when the air-fuel mixture is ignited by a hot object/area in the combustion chamber before the timed spark event occurs. When the spark plug firing end (tip) temperature exceeds 800°C, pre-ignition originating from the overheated insulator ceramic can occur. Pre-ignition will dramatically raise the cylinder temperature and pressure and can cause serious and expensive engine damage. When inspecting a spark plug that has experienced overheating or pre-ignition, blistering on the ceramic insulator and/or melted electrodes can sometimes be found.

Edited by mxn4life

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Somefactors to consider in selecting the proper heat range spark plug

There are many external influences that can affect the operating temperature of a spark plug. The following is a brief list to consider in avoiding reduced performance and/or expensive engine damage.

Engine Speed and Load

If the engine is to be operated at high RPM, under a heavy load, or at high temperatures for long periods a colder heat range may be needed.

Conversely, if the engine is to be operated at low speeds or at low temperatures for long periods, a hotter heat range might be needed to prevent fouling.

Air-Fuel Mixture

Excessively rich air-fuel mixtures can cause the plug tip temperatures to decrease and carbon deposits to accumulate, possibly causing fouling and misfires.

Excessively lean air-fuel mixtures can cause the cylinder and plug temperatures to increase, possibly resulting in knock and/or pre-ignition. This may cause damage to the spark plug and/or seriously damage the engine.

If an air-fuel ratio meter or gas analyzer is not available, it will be necessary to visually inspect the spark plugs frequently during the tuning process to determine the proper air-fuel mixture.

Fuel Type / Quality

Low quality and/or low octane fuel can cause knock which will elevate cylinder temperatures. The increased cylinder temperature will cause the temperature of the combustion chamber components (spark plug, valves, piston, etc.) to rise, and will lead to pre-ignition if the knock is uncontrolled.

When using an ethanol blend fuel with high ethanol content in high performance applications, a colder heat range may be necessary. The spark timing can be advanced further because ethanol blend fuel has a higher resistance to knock (higher octane). Due to the decreased knock, there will be less audible “warning” from knock before the spark plug overheats and pre-ignites.

Some types of fuel additives in lower quality fuels can cause spark plug deposits that can lead to misfires, pre-ignition, etc.

Ignition Timing

Advancing ignition timing by 10° will cause the spark plug tip temperature to increase by approximately 70° to 100°C.

A colder heat range spark plug may be necessary if the ignition timing has been advanced to near the knock level. Higher cylinder temperatures near the knock level will bring the spark plug firing end temperature closer to the pre-ignition range.

Pre-ignition will dramatically raise the cylinder temperature and pressure and can melt and hole pistons, burn valves, etc.

Knock

Occurs when part of the air-fuel mixture in the combustion chamber away from the spark plug is spontaneously ignited by the pressure from a flame front originating from the spark plug. The two colliding flame fronts contribute to the “knocking” sound.

Knock occurs more frequently when using low octane fuel. Low octane fuel has a low resistance to knock (low resistance to ignition)

Knock is related to ignition timing. (Knock is sometimes referred to as “Spark-knock”.) Retarding the ignition timing will reduce knock.

Heavy knock often leads to pre-ignition.

Heavy knock can cause breakage and/or erosion of combustion chamber components.

Knock is sometimes referred to as “ping” or “detonation”.

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After doing some research I think your motor was experiancing pre ignition.

Post some pics!

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Good plug information guys. On the bike, I would bet you had an air leak show up for the dance. However, any time you burn the tip off the plug it goes back to lean jetting (or air leak) or wrong heat range. I bet the plug was light gray and the top of the head and piston was gray. Hope it all works out for you.

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So the plugs are two different sizes?

I guaranty there is no difference in size between an ES and an EG.

If your electrode was fryed there is another reason.

More than likely it was super lean and your piston shatterd and ate your plug electrode.

I also guarantee there is no difference in spark plug sizes between ES and EG (obviously). This is not what I meant

I'm not too sure about on RM125's but I know on RM250 (and RMX) there were vibration/resonance issues where the electrode tang would break off as you describe. An EG type plug has a much stronger tang which will handle the vibration.

I thought this may have happened to you.

There should be some other evidence if it was due to a lean condition plus you would have had some major pre-ignition before it failed

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I also guarantee there is no difference in spark plug sizes between ES and EG (obviously). This is not what I meant

I'm not too sure about on RM125's but I know on RM250 (and RMX) there were vibration/resonance issues where the electrode tang would break off as you describe. An EG type plug has a much stronger tang which will handle the vibration.

That would be the first time Ive ever heard of that happening. I've seen where electrodes exploded before.

I Would love to see pictures of the carnage, Dirt addict.

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I also guarantee there is no difference in spark plug sizes between ES and EG (obviously). This is not what I meant

I'm not too sure about on RM125's but I know on RM250 (and RMX) there were vibration/resonance issues where the electrode tang would break off as you describe. An EG type plug has a much stronger tang which will handle the vibration.

That would be the first time Ive ever heard of that happening. I've seen where electrodes exploded before.

It is pretty well documented if you care to look around, both on Rm125 & 250's. I thought it was sorted by 03 though.

Have a look here:

http://www.dirtrider.net/forums3/showthread.php?threadid=80271

http://www.dirtrider.net/forums3/showthread.php?t=150214&page=1&pp=10&highlight=rm+electrode

Never heard of it.......?

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sorry guys i just looked back here. the plug is the oem for the 03 rm125. its got a funky number. the part that came off is the outside metal "L" part. (just read that its called the ground strap) it banged around in there for a few seconds at max rpm's. the piston is intact but pitted bad. same with the head, the walls are scored. its already boxed up or i'd take pics. here's the oddity - the plug has a nice mocha color to it. i was running stock jetting. 32:1 . i was at 3200' asl, temps in the70's. i shoulda been rich. i was running it hard. some steep hills out of a sand pit track. i'm 200#'s.

i opened up the carb last nite and saw the float level was off. it was about 5.5mm. should be 8.7 +- 1mm. but that should make it run rich right?

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You would hope to have been safe with $30 OEM plug!

Like you say, the pitting on piston and head definitely sound like lean condition but you would have expected a nasty white blistered plug to collaborate that though.

Not too sure on float height, too small a measurement (from gasket face) should give you too much fuel causing overflow, I think 👍

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thanks for the input guys. im shipping it off to Eric Gorr tomorrow. hopefully the turnaround isnt too bad. these 125's are so fun! i was battling yesterday with a guy that is slightly faster than me. it took him a few laps to pass, and then it was on one of the hills coming out of the pit. he had me by 325cc's....

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It is pretty well documented if you care to look around, both on Rm125 & 250's. I thought it was sorted by 03 though.

Have a look here:

http://www.dirtrider.net/forums3/showthread.php?threadid=80271

http://www.dirtrider.net/forums3/showthread.php?t=150214&page=1&pp=10&highlight=rm+electrode

Never heard of it.......?

Yeh thats bannanas, look at what NGK said.

http://www.dirtrider.net/forums3/sh...=plug+vibration Pay particular attention to Post #5 in this thread

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Sure is some scary reading 👍

Particularly scary when NGK admit a fault. I wonder how long and how many bikes were rebuilt before they brought about the design change.

I had always been under the impression NGK B??EG plugs and Denso W16ES-/U (equivalent), overcame these problems.

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Sure is some scary reading 👍

Particularly scary when NGK admit a fault. I wonder how long and how many bikes were rebuilt before they brought about the design change.

I had always been under the impression NGK B??EG plugs and Denso W16ES-/U (equivalent), overcame these problems.

So those posts were from 2007 I wonder if the new style rms are having that problem

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