SX 250 Piston wear

MZ193
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MZ193
Edited Date/Time 10/25/2020 7:52am
Hello guys
I just got a "new" SX 250 2019.
56 hours in it.
The old owner told me he did the piston at 44 hours.

Here is the piston:
Does it look like a 12 hours piston or is this the original one?



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JWACK
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JWACK 10/24/2020 8:04am
10/24/2020 8:04am
Look at the nuts that hold the cylinder to the crankcase. Do they have fresh tool marks?
Your piston looks ok to me.
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MZ193
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MZ193 10/24/2020 8:38am
10/24/2020 8:38am
JWACK wrote:
Look at the nuts that hold the cylinder to the crankcase. Do they have fresh tool marks?
Your piston looks ok to me.
Yeah. It looks like it has been opened.
What do you think?

JWACK
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JWACK 10/24/2020 8:41am
10/24/2020 8:41am
JWACK wrote:
Look at the nuts that hold the cylinder to the crankcase. Do they have fresh tool marks?
Your piston looks ok to me.
MZ193 wrote:
Yeah. It looks like it has been opened. What do you think? [img]https://p.vitalmx.com/photos/forums/2020/10/24/455696/s1200_5B905BEE_F603_4F9F_93C5_933B6271DB8D.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2020/10/24/455697/s1200_60E58FD7_DFE6_434C_A7CF_4B6FE706511B.jpg[/img]
Yeah. It looks like it has been opened.
What do you think?

I would say it has.
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Boomslang
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Boomslang 10/24/2020 8:47am
10/24/2020 8:47am Edited Date/Time 10/24/2020 8:55am
The old owner speaks the truth. You have nothing to worry about.
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friday10
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friday10 10/24/2020 8:58am
10/24/2020 8:58am
I think they recommend replacing every 20 hours?
MZ193
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MZ193 10/24/2020 9:12am
10/24/2020 9:12am
friday10 wrote:
I think they recommend replacing every 20 hours?
Yeah, and oil every 30 minutes.
All of my friends on sx/tc 250 are doing 40/60 hours on top end, 100/140 hours on crank/bearings.
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Blade Flanagan jr. 10/24/2020 9:48am
10/24/2020 9:48am
That is a fresh top end for sure. No blow by past the rings and nice horizontal machining marks on the skirt. I've done top ends on those bikes way past 60 hrs. and they still looked good. Air filter maintenance is the key.
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BobPA
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BobPA 10/24/2020 10:21am
10/24/2020 10:21am
friday10 wrote:
I think they recommend replacing every 20 hours?
MZ193 wrote:
Yeah, and oil every 30 minutes.
All of my friends on sx/tc 250 are doing 40/60 hours on top end, 100/140 hours on crank/bearings.
I've got 80 some hours on my 300, and it still runs perfect. Compression is the same since new. Put a piston in my friends 300 at 88 hours and it spec'd perfect, ring end gap was well within spec. My other bro pushed his to 150 hours before a piston change....that's a bit long for my taste, but it lasted.

Riding style varies between all of us as well.
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bvm111
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bvm111 10/24/2020 10:38am
10/24/2020 10:38am
You can see the chamfer on the rings and looks good to me!
AJ565
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AJ565 10/24/2020 5:19pm
10/24/2020 5:19pm
So I’m gonna point out that the nuts and bolts look like they’ve been tightened down. I don’t see witness marks that they’ve been loosened.

Also in terms of wear this is my piston with 90 hours on it and it has about the same wear.

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captmoto
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captmoto 10/24/2020 5:25pm
10/24/2020 5:25pm Edited Date/Time 10/24/2020 5:26pm
You know that every seller that says fresh top end is a liar don't you? I learned that here on Vital.
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huutnanny
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huutnanny 10/24/2020 7:09pm
10/24/2020 7:09pm
Really you should look at the old piston. That will tell the story if anything is going on
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Lightning78
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Lightning78 10/24/2020 7:22pm
10/24/2020 7:22pm Edited Date/Time 10/24/2020 7:23pm
Blade Flanagan jr. wrote:
That is a fresh top end for sure. No blow by past the rings and nice horizontal machining marks on the skirt. I've done top ends...
That is a fresh top end for sure. No blow by past the rings and nice horizontal machining marks on the skirt. I've done top ends on those bikes way past 60 hrs. and they still looked good. Air filter maintenance is the key.
I bought a pretty low hour 2003 kx250 that had been ridden but clearly still somewhat low in the hours. I've owned it for a year and a 1/2 and towards the end of last season the compression was getting low so I knew it knew the piston had to be replaced.

Low and behold my surprise when I cracked that engine open for the very 1st time it still had the original piston in it after 17 years including the rings ! The engine had never been opened until I put a new top end in it about 2 months ago.
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POWLEY256 10/25/2020 1:46am
10/25/2020 1:46am
Just throw a new piston in it then you know for sure, 2stroke pistons are cheap enough and easy enough to swap out. Why risk it? I always throw a new piston in if i buy a second hand bike no matter what the hours. Its easy to disconnect the hour meter once it gets to a certain point so you can never trust a second hand bike.
MZ193
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MZ193 10/25/2020 2:38am
10/25/2020 2:38am
What piston do you recommend for my bike?
foreman52
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foreman52 10/25/2020 5:43am
10/25/2020 5:43am
If you’re concerned about it just put a new one in. It is super cheap to do and gives you the peace of mind you’re looking for. Otherwise it may end up like mine this summerDry

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