2003 Rm 125 engine failure. HELP!

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7/13/2018 9:13 AM
Edited Date/Time: 7/13/2018 9:20 AM

Hey guys, I am very new here, but am in need of some advice. My bike ate a brand new piston I put in it after 5 minutes of riding (wiesco). The original reason for replacing the piston and honing the sleeved cylinder was that the bike overheated due to a broken coolant line on the trail. Mind you, I did the (failed) rebuild about 2 1/2 years ago. The reason for this is I joined the military shortly after my bike died.
So after I rebuilt the top end and resealed everything, I started it up with no apparent issues. I let it idle for 5 minutes max, then I took it out on the road to test. It ran good unless I went WOT; this caused it to completely bog. I wasn't surprised however because I had thrown all new jets in and I hadn't figured out the perfect mixture ratio yet.
About 5 minutes down the road I started to lay into it a bit more and more and then failure. The bike died and wouldn't start back up. The piston was not seized and was completely free. I am now at the point where I am finally able to take a look inside the engine.
The sleeve had a good amount of scoring and was beyond the point of rehoning. The piston is gauged up and has a bunch of scoring. The ring is locked in place at one specific spot and there is a half inch wide and a millimeter deep recession above this same spot.
Now my thinking is, my younger inexperienced self threw the engine together and didn't torque the head and jug down and there was too much room for the piston to catch on a lip which sent the piston pieces around the cylinder causing the damage. However, I'm not 100% sure and would like as many knowledgeable opinions as possible.
I just purchased a brand new oem jug and weisco piston. So my questions to you guys are:
What do you think caused this?,
If I install a new jug and piston will this failure reoccur?,
What are the next steps to getting this bike on the trail again?
Thanks guys! If this is not enough information, let me know and I will try to provide more Photo.
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7/13/2018 9:28 AM

Sorry bro but soon as you said wiseco.. I knew what had happened... don’t run that garbage.. for future OEM or pro x

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7/13/2018 9:54 AM

Clear case of detonation, this is pretty common with low octane fuel, or possible lean condition (jetting, air leak)

This is your best friend for diagnosing these kind of issues:

https://www.eric-gorr.com/files/pdfs/2_stroke_top_end_and_performance.pdf


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7/13/2018 9:54 AM
Edited Date/Time: 7/13/2018 12:05 PM

The exhaust side seem to have over heated and seized. This is common with forged pistons if several heat cycles are not done prior to putting a load on the engine.
Does you exhaust port in the engine have a bridge in it?
If so why were the lubricating holes not put in the piston ?
Was that bridge relieved?
Was the piston to cylinder fix checked to be proper?
Was the ring end gap checked?
Was the squish checked?
Was the original piston a dome unit or a flat top unit?
Remember that a sleeved cylinder does not transfer heat as well as a plated unit. It also requires a longer warm up before placing a load in it as the piston will expand faster that the sleeve.

Paw Paw

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7/13/2018 10:40 AM

mwssquad827 wrote:

Sorry bro but soon as you said wiseco.. I knew what had happened... don’t run that garbage.. for future OEM or pro x

Lol no

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7/13/2018 10:58 AM

mwssquad827 wrote:

Sorry bro but soon as you said wiseco.. I knew what had happened... don’t run that garbage.. for future OEM or pro x

kb228 wrote:

Lol no

Lol yes

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7/13/2018 11:32 AM

mwssquad827 wrote:

Sorry bro but soon as you said wiseco.. I knew what had happened... don’t run that garbage.. for future OEM or pro x

kb228 wrote:

Lol no

mwssquad827 wrote:

Lol yes

Lol no

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7/13/2018 12:28 PM

Put the stock jetting back in it. How many steps leaner were the jets you "threw" in it ?

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7/13/2018 1:07 PM

Paw paw
Honestly I didn't do any of those things. I slapped a piston on the rod, honed the cylinder and ran it. I see how completely stupid that was now. Seems like the piston and exhaust bridge were contacting.

Project racer
It's been so long I don't remember. The most I can tell you is I put in a JD jetting kit.

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7/13/2018 1:13 PM

The problem is the brand of piston you used...

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7/13/2018 1:28 PM

Really? I've only heard good things from wiseco.

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7/13/2018 1:30 PM

mwssquad827 wrote:

The problem is the brand of piston you used...

No it isnt

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7/13/2018 1:32 PM

tom_rm_125 wrote:

Really? I've only heard good things from wiseco.

Ignore him

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7/13/2018 1:42 PM

tom_rm_125 wrote:

Really? I've only heard good things from wiseco.

Ignore him. I've only ever bought wiseco pistons for my rebuilds. I've never once had an issue. The guy is being a douche... Answer as many of Paw Paw's questions as you can and he'll help give an educated opinion.

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7/13/2018 3:48 PM

Paw paw
There is a bridge but it wasn't relieved and I have no idea why I didn't drill lubrication holes.
The squish and ring end gap was not addressed either. It seems there could have been a slew of reasons why it turned out the way it did. Thanks for the info on the warm up/heat cycles by the way I didn't know that was a common issue.

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7/13/2018 4:04 PM

FYI: I have not failure issues with that brand of pistons in 2 strokes either. The bridge thing is a big issue and needed piston drilling as is the heat cycles. In some cases using the forged piston in a sleeved cylinder I have had to run the engine through a few heat cycles and then tear it down and sand the piston skirts to get the proper fit.
The best thing you can do is to have the cylinder replated and start from scratch and do it right. They can plate sleeved cylinders now and it works well, but a plated alloy non sleeved cylinder is your best bet.
Remember that the use of a sleeved cylinder is best suited for a non forged piston due to the heat exchange thing and thus the life will be very short.
Good luck!

Paw Paw

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7/13/2018 5:45 PM

I have had issues and so have the people I r ide with... so I’m not being a douche..


But paw paw does know what he is talking about.. very smart dude

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7/13/2018 6:48 PM

mwssquad827 wrote:

I have had issues and so have the people I r ide with... so I’m not being a douche..


But paw paw does know what he is talking about.. very smart dude

Youre probably doing something wrong. Top 3 brands of pistons is JE CP and Wiseco. Youre probably thinking of wiseco cranks... those are bad.

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7/13/2018 11:03 PM

mwssquad827 wrote:

I have had issues and so have the people I r ide with... so I’m not being a douche..


But paw paw does know what he is talking about.. very smart dude

kb228 wrote:

Youre probably doing something wrong. Top 3 brands of pistons is JE CP and Wiseco. Youre probably thinking of wiseco cranks... those are bad.

How did you get your top 3 pistons?

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