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Discussion Starter · #1 ·
Hi , i purchased a 125 sx a couple of months ago and the old owner claimed the bike had 10 hours since a rebuild 馃ぃ doesnt look it to me but im not sure

should i change my piston ? And how does the cylinder look from these photos
It looks like blow by and im hoping the cylinder will be still goot to use , fingers crossed
Can i run this any longer ?

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Keir, you can't really tell looking through the exhaust port. No obvious blowby which is more brown staining as opposed to oil. Everybody selling a small 2T claims to have done a recent piston change, just a fact of life. I would always treat these claims as suspect. If you aren't happy, go for a piston change,10 hours is getting near the useful end of life anyway. then you will know where you are at with your maintenance schedule. Having said all that, we have an old 2016 125sx in our workshop with new mains, rod bearing and gearbox bearings (done just because the cases were split). I also stuck in a new piston and it's done less than an hour - will I be believed if we decide to sell it? Who knows lol Bob
 

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Discussion Starter · #4 ·
Keir, you can't really tell looking through the exhaust port. No obvious blowby which is more brown staining as opposed to oil. Everybody selling a small 2T claims to have done a recent piston change, just a fact of life. I would always treat these claims as suspect. If you aren't happy, go for a piston change,10 hours is getting near the useful end of life anyway. then you will know where you are at with your maintenance schedule. Having said all that, we have an old 2016 125sx in our workshop with new mains, rod bearing and gearbox bearings (done just because the cases were split). I also stuck in a new piston and it's done less than an hour - will I be believed if we decide to sell it? Who knows lol Bob
Yeah fair comment , planning on doing it anyway for a piece of mind , atleast i know it will be good i hope the cylinder wont need re plating but if so i have heard good things from langcourt
Have you used them before ? And if so what is the pricing for a re plate ?
 

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Well you won't know condition of cylinder until you take it off. Rule of thumb is it needs a replate if you can feel a ridge with your thumbnail where the top ring stops when piston at tdc. If not, and no scrapes, then that will be fine. The nikasil tends to wear above the exhaust port first and goes a darker colour. The lines you see on the piston in the photos are quite normal. I've used Langcourt a few times, always done a good job - you have to strip the pv just leaving the 3 mounting pins or they charge you for doing it. They weld up any damage and tidy the ports then sandblast the exterior all for under 拢200, which is cheap for what is a new cylinder. Beware of going via a shop offering a silly quick turn around as you probably won't get your own cylinder back which can have added problems. However, feel you are jumping the gun, sure your cylinder will be ok unless you've not mentioned any issues. If you need any help just post up, I've done dozens of 125 piston changes over the years, as have others on the forum no doubt. Bob.
 

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Discussion Starter · #6 ·
Well you won't know condition of cylinder until you take it off. Rule of thumb is it needs a replate if you can feel a ridge with your thumbnail where the top ring stops when piston at tdc. If not, and no scrapes, then that will be fine. The nikasil tends to wear above the exhaust port first and goes a darker colour. The lines you see on the piston in the photos are quite normal. I've used Langcourt a few times, always done a good job - you have to strip the pv just leaving the 3 mounting pins or they charge you for doing it. They weld up any damage and tidy the ports then sandblast the exterior all for under 拢200, which is cheap for what is a new cylinder. Beware of going via a shop offering a silly quick turn around as you probably won't get your own cylinder back which can have added problems. However, feel you are jumping the gun, sure your cylinder will be ok unless you've not mentioned any issues. If you need any help just post up, I've done dozens of 125 piston changes over the years, as have others on the forum no doubt. Bob.
Alright thanks , will keep that in mind and no issues at all tbh starts first or second kick , compression doesnt feel as good as it could be apart from that there is no piston slap or any weird sounds so will probably replace the piston. Also my cylinder looks to be the newest thing on the bike ahaha it looks as it has already been sandblasted or vapor honed already which is a positive sign

cheers for you help Bob , you鈥檝e answered almost everything ive asked 馃憤
 

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All the replate companies stamp numbers and/or letters on the cylinder base (the sort of flat part between the 2 base nuts at the back so if you look there and anything there it's had a replate sometime. Bob
 
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