Rm125 keeps BLOWING UP!

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5/13/2018 7:01 PM

So i just finished my 2007 rm125 build and i have around 3 hrs total on the bike and I’m now on my second top end. The first blow up had me replace everything up top so it’s l now oem stock. Brand new cylinder, head, piston and power valve. So it blowing up after fresh oem parts has me confused. It looks like it hit the power valve. Any ideas? Photo Photo Photo Photo Photo Photo

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5/13/2018 7:05 PM

Photo
This is the first blow up
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5/14/2018 2:56 AM

Is the power valve timed right? If so id break out the calipers and measure everything to make sure its within spec. If all that is good, the crank is probably the culprit.

Looks like blowby on the piston. Was ring to cylinder clearance correct?

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5/14/2018 6:17 AM

Could be a piece of piston ring from previous blow up.

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5/14/2018 7:09 AM

kb228 wrote:

Is the power valve timed right? If so id break out the calipers and measure everything to make sure its within spec. If all that is good, the crank is probably the culprit.

Looks like blowby on the piston. Was ring to cylinder clearance correct?

Well everything was oem stock so i figured it should be good and i did not assemble it. I probably should have and went through all the numbers. How would the crank cause this?

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5/14/2018 7:13 AM

metal_miracle wrote:

Could be a piece of piston ring from previous blow up.

I would maybe think that if it was in a different spot but the way it looks the same on both blow ups it has to be a certain problem.

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5/14/2018 8:29 AM

Looking at that plug using my phone it looks lean/gray. Should be light to med. brown. At the front/top of the piston, it shows it’s degraded the edge like the bike had pre-ignition.

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5/14/2018 10:27 AM

For sure the second piston had some bad detonation and pinged away at the ring groove until the ring caught the exhaust port and boom!. If all is stock, the question is why are you having detonation problems???

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5/14/2018 10:50 AM

The plug has a good color to it it might be a cunt hair lean but i have seen way leaner. It is a lectron carb i am running an i have sent info to them to see what they think. Im running 32:1 oil 50/50 vp4.4 pump 91. (Yes i know stock motor should not need race fuel but has more pep)

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5/14/2018 11:49 AM

I doubt this is your problem and I’m not sure if you know this but the rms require a special plug that ngk makes. I’ve already saw someone else’s blow up because they’re not using the correct plug.

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5/14/2018 12:05 PM

zac_k3 wrote:

I doubt this is your problem and I’m not sure if you know this but the rms require a special plug that ngk makes. I’ve already saw someone else’s blow up because they’re not using the correct plug.

Ya I’m running that 35 dollar plug

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5/15/2018 5:24 AM
Edited Date/Time: 5/15/2018 5:28 AM

I'm not familiar with the '07 but I thought other RMs have a vertical bridge in the center exhaust port. Is the port totally open with no bridge? To clarify I'll send a pic with what I believe to be original cylinder . My point is that if your cylinder has been modified could be source of your issues.Photo

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StuntmanStew

5/15/2018 7:54 AM

Stuntman_600 wrote:

I'm not familiar with the '07 but I thought other RMs have a vertical bridge in the center exhaust port. Is the port totally open with no bridge? To clarify I'll send a pic with what I believe to be original cylinder . My point is that if your cylinder has been modified could be source of your issues.Photo

Ya that bridge is there i bought a brand new one from Suzuki that is stock.

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5/15/2018 7:56 AM

This is the front of the piston. (Intake)makes me think a hot spot happened there first. Photo

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5/15/2018 3:29 PM

Is your piston in backwards? Looks like the ring retainer and gap is at the front in the pictures?

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5/15/2018 4:57 PM

piston in backwards

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5/15/2018 9:13 PM

Piston is not in backwards like i said in that photo that is the intake side.

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5/16/2018 4:55 AM

She is lean, piston is getting hot and the ring is moving in the softened piston and catching in the port. try leaded race gas and a bigger main jet.

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5/16/2018 10:22 AM

Ross_McWatters wrote:

She is lean, piston is getting hot and the ring is moving in the softened piston and catching in the port. try leaded race gas and a bigger main jet.

Ya i been leaning on that side of things that i need to fatten it up a lil

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