spark plug gap is closing?

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8/7/2018 8:25 AM

2003 rm 125, the spark plug arm is bending up and completely closing the gap after about 3 laps (6 minutes), happened twice in a row after a long wide open straight. replace the plug and it runs perfect until this happens again. Previous to this the whole engine was rebuilt with new everything except transmission. Cylinder was replated and bored with the head matched to it and a new piston. everything was installed correctly. Powervalve assembly was taken apart and cleaned with the exhaust valves replaced and trimmed down for the cylinder bore. Everything on the bike is new and at spec. I am at a loss for what is causing this? and yes I did the heat cycles before opening it up. Any help or ideas would be GREATLY appreciated!

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8/7/2018 8:31 AM

Piston hitting it?

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8/7/2018 8:37 AM

kb228 wrote:

Piston hitting it?

That was my initial thought, but the arm isn't showing damage its just evenly bent upward.

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8/7/2018 10:27 AM
Edited Date/Time: 8/7/2018 10:27 AM

Maybe the use of a domed piston in a flat top piston head/ cylinder combo. Also excess heat or poor quality plug can cause this as the tip gets too hot.
Check you squish to make sure you are in spec.

Paw Paw

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8/7/2018 10:44 AM

Right around that time Suzuki was running some flat top and some domed pistons in their 125's, depending on the year.

You might be able to use the depth bar on a set of dial calipers to figure out how close the piston is getting to the plug at TDC.

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8/7/2018 2:08 PM
Edited Date/Time: 8/7/2018 2:09 PM

Are you using the right plug? Those rm125s take a special plug

SPARK PLUG (NGK,R6918B-8)
Mfg. #09482-00509

$25 each on rocky mountain

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8/7/2018 5:37 PM
Edited Date/Time: 8/7/2018 5:38 PM

Hondas4Life3 wrote:

Are you using the right plug? Those rm125s take a special plug

SPARK PLUG (NGK,R6918B-8)
Mfg. #09482-00509

$25 each on ...more

X2. I built a rm125 02, I think, and it too needed a special plug

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8/8/2018 6:01 AM

Paw Paw 271 wrote:

Maybe the use of a domed piston in a flat top piston head/ cylinder combo. Also excess heat or poor quality plug can cause ...more

I will have to check out the flat/dome piston and see if i'm running the wrong one. As for the spark plug i have run a br9eg plug in previous rm 125s and never had a problem. I guess if the piston is right i will try the better plug, but i'd hate to bust up a 25 dollar sparkplug if its not needed

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8/8/2018 6:03 AM

Also I was told to look at the timing and that it could cause this and it was slightly off so I got that centered back up and will see if this fixes my problem as well

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8/8/2018 2:19 PM

If you have faced this problem and didn't solve it out then I'll recommend you to take a help fromms OneNote customer service to fix this issue and hope it will permanently remove the problem.

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8/8/2018 2:43 PM

sarahjones wrote:

If you have faced this problem and didn't solve it out then I'll recommend you to take a help fromms OneNote customer service ...more

Scammer

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8/8/2018 4:56 PM
Edited Date/Time: 8/8/2018 4:56 PM

Husky82 wrote:

I will have to check out the flat/dome piston and see if i'm running the wrong one. As for the spark plug i have run a br9eg ...more

Seems easier than taking the engine apart. As also stated above timing will do that

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8/8/2018 5:56 PM

From what I remember the RM's that required the special plug did so because normal plugs could have the strap break off due to some harmonics that those engines could produce. The high dollar plug's electrode is "extra welded" to the plug body so that won't happen.

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