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2001 yz125 engine problem

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I took my engine apart and I realized the piston and the cylinder head has these little dents in it like someone stabbed it with a knife. I also noticed when the piston goes down on the stroke it makes a air sound coming from the piston ring gap. Is that normal? I will give a link to my YouTube video I made for you guys to check out. Also, is it normal for it to have that brown ring on it? I only rode it for about 10 hours so far. I'm new here but not new to mechanics but some stuff like this is just bleh. 

 

This is it right when I took the cylinder head off to inspect the problems. Notice when it gos down it let's air in to the top of the piston. I dont know if this is supposed to happen.

 

 

Like I said, I ain't a master to mechanics, but I know a difference between a lug wrench and a screwdriver. :)

Here's a pic of the piston after I took the cylinder head off. It had these little gouges in the metal and all these little dots on it.

Please help me with this 

20170418_221002.jpg

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Pitting is common with older bikes and is just caused from detonation.  it dosent affect performance of life of your bike if your scared of that ,but if it bugs you you can just send it into a shop and get it polished for about $50 bucks or get a dremel and sand it down yourself and save some money   just be careful and make sure things are even if you do it yourself

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17 minutes ago, braapktmbraap said:

Pitting is common with older bikes and is just caused from detonation.  it dosent affect performance of life of your bike if your scared of that ,but if it bugs you you can just send it into a shop and get it polished for about $50 bucks or get a dremel and sand it down yourself and save some money   just be careful and make sure things are even if you do it yourself

you mean that detonation causes the little chips in the piston? theres little sharp flakes gouged into the piston but i looked and i couldnt find anything that small that couldve broke and caused that. the little chips were all around the piston if that makes any sense**

Edited by motocrossmike 759

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from the picture all i can tell it that theyre   scratched and pitted  but if you think its something else id definitely check everything else out too   on a more similar case on another 125 the piston was chipping from the edge of the exhaust port chipping si id just run through your cylinder and make sure theres no contact to things that dont need contact.

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2 minutes ago, braapktmbraap said:

from the picture all i can tell it that theyre   scratched and pitted  but if you think its something else id definitely check everything else out too   on a more similar case on another 125 the piston was chipping from the edge of the exhaust port chipping si id just run through your cylinder and make sure theres no contact to things that dont need contact.

do you think it couldve been a piece of debris from something in the air filter? i put the bike back together again and now im gonna have to take it all apart again. lol, oh well

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The damage shown on the piston's crown is more apparent to debris bouncing around then detonation (which looks more like sandblasting),

check up/down play of the connecting and if anything looks weird in the rods bearings (discoloration etc.)

Have any clearances ever been measured ? (ring end gap, piston to bore etc.)

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5 minutes ago, mlatour said:

The damage shown on the piston's crown is more apparent to debris bouncing around then detonation (which looks more like sandblasting),

check up/down play of the connecting and if anything looks weird in the rods bearings (discoloration etc.)

Have any clearances ever been measured ? (ring end gap, piston to bore etc.)

i checked ring end gap and it was fairly small. i didnt get to check it with a feeler gauge.

heres food for thought. i was riding it yesterday along the tracks for quite a distance to get to these boat ramps, and i was holding it 3/4 - WFO. i felt it do something wierd where i was slowing down, or going a slower speed, and i felt a bump and it pushed the bike a little bit im not too sure what it could be?

i havent checked piston to bore clearance because i dont have one of those tools, it is a new top end, and theres aliminum chips in those holes on the top of the piston & cylinder head. when you rub over them a little piece would come out.

im hoping its nothing too serious :/

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Not measuring any clearances, aluminium chips lying around, engine dying down after some WOT....yep doesn't sound too serious...

You will no doubt sooner rather than later have to tear it down again and get the chance to inspect & rebuild it properly.

Edited by mlatour

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it runs perfectly fine, maybe it was a speckle from somethiong in my air filter after i cleaned it recently, or it couldve been detonation since i advanced my timing 2mm... i was using 98 octane gasoline and advanced my timing so i tuned it back and it feels better. i think having the advanced timing wasnt doing what i intended it to do. but in a bit i will buy all new gaskets, seals, bearings, and other shit and i will do a whole rebuild on the bike. im the type of person that if i do something, i either do the entire thing over, or i just do nothing about it haha :thumbsup: 

but on another note, what is that sound coming from my piston in my video? when the piston goes down, it makes a air passing sound. someone tell me if its normal please

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On a 2-stroke, during the compression stroke the crankcase creates a vacuum that sucks in a charge from the intake, (reeds, carb, air filter)

once trapped (ports blocked off by the piston), on the downward (power) stroke the intake charge that got trapped in the crankcase

gets pumped to the combustion chamber (top of piston) thru the transfer ports.

 

https://en.wikipedia.org/wiki/Two-stroke_engine#/media/File:2-Stroke_Engine_ani.gif

Edited by mlatour

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2 minutes ago, mlatour said:

On a 2-stroke, during the compression stroke the crankcase creates a vacuum that sucks in air from the intake,

once trapped (ports blocked off by the piston) on the downward stroke, the intake charge that got trapped in the crankcase

gets pumped to the combustion chamber (top of piston) thru the transfer ports.

what about the leaking sound coming from the downward stroke? shouldnt it be compressing and then releasing the air all at once on the stroke? or should it be letting some air pass by, and then once it gets to the intake port it should release the rest of the air..?

i know that its compressing, decompressing on both sides of the piston on a two stroke, i just dont know if its a problem on mine or not.

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If the plating is worn, cylinder worn / out-of-round

piston size not matched properly to the cylinder

ring end gap too wide

ring not broken in / glazed over (cylinder cross-hatch worn away)

 

that can all prevent the piston from sealing tightly and 'leak' some crankcase pressure.

 

Of course you have to take into consideration the engine is not up to it's normal operating temps

so parts are 'out-of-round' until they expands to their 'intended' shape and fit. 

Reason why a compression test preferably not done on a cold engine.

Edited by mlatour

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1 minute ago, mlatour said:

=

If the plating is worn, cylinder worn / out-of-round, 

piston size not matched properly to the cylinder,

ring end gap too large, piston ring not properly set/broken in 

that can all prevent the piston from sealing properly and 'leak' some crankcase pressure.

the piston, cylinder, and rings all came as a kit from athena and i broke it in properly. i let it warm up first then i just it off, and let it cool down all the way. i did it about 2 times, then i got on it and rode down the street a bit and got it warmed up again, then i took it to the tracks and i started getting on the pipe :ride: 

but im curious to that sound since it should be sealed right? you got to wear headphones to hear the sound, it sounds like a pfft almost. but im going to get a new ring and then listen to see if i hear the same sound. if i do, then im just gonna leave it at that

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By your description I'd say your break-in procedure is too easy.

Measure you end gap before ordering a new ring. 

Since this one has relatively few hours on it, if the gap is way out of spec, it could be an indication of a worn cylinder.

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