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need help 05 yz 125 blew up!!! need advice! pictures

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well the 125 blew up with about 25 hours on it and it looks like it was running HOT. All stock but a fmf sst pipe. 410 main, 35 pilot, stock needle. I need advice on whether or not I need to get a new jug. The pitting on top is on the exhaust side, the almost burned a hole trough the bottom of the piston! when I run my finger over the top of the piston i can feel a "dip" in it...not good. I was thinking about doing the Eric Gorr 144, but my question for that is for 500 bucks does he bore the cases or is that more? iI want to keep it cheap, if the jug is toast then ill go with the 144 but it is not my first choice.

well here is the jug, its pitted on the exhaust side

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the head has a little bit of pitting to it... whatcha think

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piston...

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NEW PICTURES!!

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Edited by motodavecrf450

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Sorry to hear that, but first clean that jug of yours, most likely a replate should do it.

Sharper pics would be better to see what is up with the jug. And more angles too if possible. What happened?

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I'll get some more pics up soon. Well I bought the bike used and before I even rode it I rebuilt it and there was a little pitting on it but I thought no big deal. I went riding yesterday and found an awesome natural track in the desert and did about a 25 min moto and then pop! So I just want to keep this repair cheap.

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Is the cylinder gouged or is it aluminium from the piston stuck on the cylinder, those cylinders are pretty tough.

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The cylinder does not have any scoring and noting melted on the walls. The part where the sleeve and cylinder come together is pitting away. Ill get better pictures tomorrow

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pretty sure those SST's run hot, my bud had to go quite a bit richer to get rid of detonation. He went through a cylinder and piston with damage very similar to yours...

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You mentioned that the barrel is sleeved. Is it really a sleeve, or is it a standard plated cylinder? Is the pitting only on the top of the cylinder where it mates with the head? Is the head pitted? When you put a straight edge across the top of the cylinder, is the damage pitting where metal is actually gone, or buildup where metal is added? Pitting is probably harder to fix than buildup because it will have to be welded and then machined in order to remove the voids.

How did it behave when it stopped? Did the engine seize and lockup the wheel, or did it just stop running? Might the sparkplug simply shorted because of aluminum buildup across the electrodes? There doesn't appear to be any damage to the cylinder walls or the piston, which usually happens when a seizure occurs. What does the underside of the head look like? The picture quality makes it difficult to tell, but it looks like there was a leak between the cylinder and head. That could certainly stop you in hurry.

Your best bet might be to look for a decent used cylinder on ebay. You may be able to get it back in action for $300 or less.

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The cylinder does not have any scoring and noting melted on the walls. The part where the sleeve and cylinder come together is pitting away. Ill get better pictures tomorrow

If it's sleeved, you'll have to remove the old sleeve, bore the cylinder and install the next size sleeve.

You can't plate a sleeved cylinder.

Ditch that SST, they are notorious for causing bikes to run hot and lean/ ie. cause detonation. An absolute bear to jet. JUNK!

I agree.

Your best bet might be to look for a decent used cylinder on ebay. You may be able to get it back in action for $300 or less.

Or, if your cylidner isn't sleeved, have it replated for 180$ if it doesn't need welded.

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US chrome and I believe Millenium too both offer to plate steel sleeves. So you could send that cylinder off and they do the rest. Get a piston first, the one you'd like to use. But call them up before you just take my word for it. Btter safe than sorry :bonk:

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You mentioned that the barrel is sleeved. Is it really a sleeve, or is it a standard plated cylinder? Is the pitting only on the top of the cylinder where it mates with the head? Is the head pitted? When you put a straight edge across the top of the cylinder, is the damage pitting where metal is actually gone, or buildup where metal is added? Pitting is probably harder to fix than buildup because it will have to be welded and then machined in order to remove the voids.

How did it behave when it stopped? Did the engine seize and lockup the wheel, or did it just stop running? Might the sparkplug simply shorted because of aluminum buildup across the electrodes? There doesn't appear to be any damage to the cylinder walls or the piston, which usually happens when a seizure occurs. What does the underside of the head look like? The picture quality makes it difficult to tell, but it looks like there was a leak between the cylinder and head. That could certainly stop you in hurry.

Your best bet might be to look for a decent used cylinder on ebay. You may be able to get it back in action for $300 or less.

It's sleeved as in the nikasil sleeve that the new bikes come with, the engine didn't lock up, the ring melted on the piston, there was not a leak between the cylinder and head because the was not any blow by or any carbon in the antifreeze. I'm think Eric gorr 144 but he just bores the cylinder that you send him but idk if mine is too messed up to bore.

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It's sleeved as in the nikasil sleeve that the new bikes come with, the engine didn't lock up, the ring melted on the piston, there was not a leak between the cylinder and head because the was not any blow by or any carbon in the antifreeze. I'm think Eric gorr 144 but he just bores the cylinder that you send him but idk if mine is too messed up to bore.

Yep 99% sure all the damaged can be fixed....makes sense to do the 144 now thru EG, but get rid of the pipe no matter what...

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To clarify: a "sleeved" cylinder has a cast-iron BORABLE sleeve pressed into the cyilnder. No OEM has done this method of cylinder production on a 125 or a 250 since the late 1980s. All OEMS use some form of nickel-silicon carbide coatings that allow for better heat transfer and much tighter piston - cylinder clearance compared to a cast-iron liner.

Your YZ125 has a "plated" surface bonded to the ID of the cylinder. When seizures happen (or when EG does a big bore kit), the plating is stripped, the bare aluminum is repaired and machined, then the cylinder is replated. Since EG has to strip the plating off to do a big bore, now is a good time to have a big bore service to your 125. Either way, the cylinder needs to be stripped, machined and replated. Why not spend 500 or so (including piston if I am not mistaken) for the big bore vs 200 (not including piston) for a replate on standard bore?

The head is usable in it's current condition.

+1 on changing pipes. I have heard / seen bad things with SSTs.

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Mine was a 250 not a 125 but my SST pipe resulted in very similar damage which luckily was caught before it failed. They are definetely a pipe where you really need to get the jetting spot on (plenty rich) and regularly check the piston for detonation damage.

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:bonk:

did you rejet the carb with the SST?

Yes, to get the detonation under control I ended up with a 185 on the main instead of the usual 175 and had to retard the ignition. With those changes it did stop the pinging but the performance then dropped off. Eventually I just stuck on a different pipe and put the jetting back and it was way better. I wanted it to work as It looked great. Stripped engine down shortly afterwards and found all the piston damage so sold pipe and moved on. All engines can be set up slightly different so if it works for you thats all that matters.:smirk:

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To clarify: a "sleeved" cylinder has a cast-iron BORABLE sleeve pressed into the cyilnder. No OEM has done this method of cylinder production on a 125 or a 250 since the late 1980s. All OEMS use some form of nickel-silicon carbide coatings that allow for better heat transfer and much tighter piston - cylinder clearance compared to a cast-iron liner.

Your YZ125 has a "plated" surface bonded to the ID of the cylinder. When seizures happen (or when EG does a big bore kit), the plating is stripped, the bare aluminum is repaired and machined, then the cylinder is replated. Since EG has to strip the plating off to do a big bore, now is a good time to have a big bore service to your 125. Either way, the cylinder needs to be stripped, machined and replated. Why not spend 500 or so (including piston if I am not mistaken) for the big bore vs 200 (not including piston) for a replate on standard bore?

The head is usable in it's current condition.

+1 on changing pipes. I have heard / seen bad things with SSTs.

That's the word I have been looking for, plated, not sleeved. Thanks for the info about Eric it seems like that is the best thing to do. And BTW the crank does not have play so that is good news

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