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How does this piston look?!! Yz125

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Hopefully the pictures could give me some info and your opinion on it.
The bike is a 2002 yz125 I bought it used in August the top and bottom end were redone in June 2015 with all oem parts. No idea with how many hours on it, I haven't done a compression test. Bike starts sometimes 1 kick normalaly 2-5 kicks. Thanks to all who help!!!

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Pictures don't say much. Imo getting exhaust pipe off is hardest part of disassembling topend. You need a feeler gauge to measure ring end gap and a fingernail to check cylinder.
Don't go too long on a 125 with an old top end.

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Piston looks pretty good. No blow by from rings. Those score marks could be from debris getting by filter.
Over all though......looks clean

Thanks, how long do you think I could run it for? Also I don't oil my filter so maybe I should....

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If you don't oil your filter then it won't last much longer and you run the risk of damaging your cylinder walls also.
Oil your filters! ..........

If you look at the last 2 pictures you can see goo cross hatching but I see some up and down lines are those bad or can I run the cylinder and when I do replace the top end what do I need to do to the cylinder? Or do I just leave it as is

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If you look at the last 2 pictures you can see goo cross hatching but I see some up and down lines are those bad or can I run the cylinder and when I do replace the top end what do I need to do to the cylinder? Or do I just leave it as is

Those up and down lines is from some debris that got down into the cylinder. It will be fine as long as the lines are not deep. Which I doubt they are.

Leave cylinder alone when you replace topend. I would make sure that I checked my ring gap

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Those up and down lines is from some debris that got down into the cylinder. It will be fine as long as the lines are not deep. Which I doubt they are.

Leave cylinder alone when you replace topend. I would make sure that I checked my ring gap

What Pistons do you recommend? Also how do I know what correct size to buy?

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5 hours ago, MrYamaHashi said:


What Pistons do you recommend? Also how do I know what correct size to buy?

Never can buy a piston without taking old one out and measuring bore/piston. 

I buy Vertex because they are second to OEM IMO. Others will say Wiseco, I say BAHHH.

Cyl/piston look pretty good.

Get an hour meter on the bike and run another 20 hours then do a top end.

Always oil your filter, otherwise you are/will destroy the engine sooner than later. 

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Never can buy a piston without taking old one out and measuring bore/piston. 
I buy Vertex because they are second to OEM IMO. Others will say Wiseco, I say BAHHH.
Cyl/piston look pretty good.
Get an hour meter on the bike and run another 20 hours then do a top end.
Always oil your filter, otherwise you are/will destroy the engine sooner than later. 

Thanks a lot I trail ride only never giving it all its got all the time, this piston probably has about 40 of my hours plus previous owner..unknown.

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2 minutes ago, MrYamaHashi said:


Thanks a lot I trail ride only never giving it all its got all the time, this piston probably has about 40 of my hours plus previous owner..unknown.

WOW!!! looks good for that many hours. Take back my 20 than. You can't see fatigue/wear on the skirt and a 125 top end change needs sooner than a 250. For piece of mind, I would get it done in the next 10 hours max to be on the safe side. It looks good and all, but a piston is only $$$ 90-125 and add a jug re-plate $$$ 185 if it explodes and scores the cylinder walls.

I always caution on the sooner and less expensive. 

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WOW!!! looks good for that many hours. Take back my 20 than. You can't see fatigue/wear on the skirt and a 125 top end change needs sooner than a 250. For piece of mind, I would get it done in the next 10 hours max to be on the safe side. It looks good and all, but a piston is only $$$ 90-125 and add a jug re-plate $$$ 185 if it explodes and scores the cylinder walls.
I always caution on the sooner and less expensive. 

Thanks for the advice I will try to get it done sooner than later just need to convince my dad since I'm 16 and you know how it goes, oh it's fine if it runs lol.

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2 minutes ago, MrYamaHashi said:


Thanks for the advice I will try to get it done sooner than later just need to convince my dad since I'm 16 and you know how it goes, oh it's fine if it runs lol.

Get the lawn mower out, rake the yard, do the dishes, keep your room clean, wash the vehicles, :smirk:heck-rub his and moms :thumbsup:feet. Puppy eyes, saying it will cost more if you don't do "preventative" maintenance. 

 

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Get the lawn mower out, rake the yard, do the dishes, keep your room clean, wash the vehicles, :smirk:heck-rub his and moms :thumbsup:feet. Puppy eyes, saying it will cost more if you don't do "preventative" maintenance. 
 

All ready do all that for the most part not foot running haha, I'm sure if I show him this he will understand!
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Don't push it. If my kid showed me a thread, I would get his but to doing more work. But alas, all mine are 20 and up, working and making money to fix their own bike. 

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Don't push it. If my kid showed me a thread, I would get his but to doing more work. But alas, all mine are 20 and up, working and making money to fix their own bike. 

That's true, I think I need to get a job somewhere and I'll buy what I need.

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You can't tell wear by those pictures. Wear has to be measured, visual inspection says the rings are still sealing so keep riding. I'm not at all sure how yz doc can see wear on a piston skirt by looking through the exhaust port, maybe x-ray vision with calipers? Anyway, doing things like this tells if you are getting blow by, which you are not. Rings wear before pistons so keep going. Once you see blowby then take it apart and measure ring end gap, do it on top, middle and bottom of cylinder to see how worn the cylinder is if you don't have a bore gauge or telescopic mic. If I were you....I would ride on.

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17 hours ago, Gary YZDOC said:

WOW!!! looks good for that many hours. Take back my 20 than. You can't see fatigue/wear on the skirt and a 125 top end change needs sooner than a 250. For piece of mind, I would get it done in the next 10 hours max to be on the safe side. It looks good and all, but a piston is only $$$ 90-125 and add a jug re-plate $$$ 185 if it explodes and scores the cylinder walls.

I always caution on the sooner and less expensive. 

 

2 hours ago, hondaman331 said:

You can't tell wear by those pictures. Wear has to be measured, visual inspection says the rings are still sealing so keep riding. I'm not at all sure how yz doc can see wear on a piston skirt by looking through the exhaust port, maybe x-ray vision with calipers? Anyway, doing things like this tells if you are getting blow by, which you are not. Rings wear before pistons so keep going. Once you see blowby then take it apart and measure ring end gap, do it on top, middle and bottom of cylinder to see how worn the cylinder is if you don't have a bore gauge or telescopic mic. If I were you....I would ride on.

Did you missread my post tiger? I'm not superman (well my wife thinks so, I can see right through her skirt). :devil:

Edited by Gary YZDOC
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Did you missread my post tiger? I'm not superman (well my wife thinks so, I can see right through her skirt). 

I know on 2 strokes especially looks are decieving. Through the exhaust port like those pictures shows a oiled up piston, if you touch it you can usually find that "wear" is oil. Especially at the bridge which is what needs to be seen on smokers....first bit of wear on cylinder every time. I haven't changed out a worn piston in so long, have such a pile of still good pistons that I refuse to touch them until I hear issues like piston clanking against cylinder or see blow by. After 27 years, never having a bike blow up....I'm over wasting money on unneeded stuff. And yeah, my wife seems to think I'm the cats ass too....if she only knew what 7 inches really looked like my cover would be blown!

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