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Thoughts about a damaged cylinder...?

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I've read as much as I could find out about this and would still like some opinions on what (if anything) I've done wrong or as to why exactly this happened. I was out riding my 2007 yz250 like normal today, then suddenly noticed my bike kept wanting to stall, so I stopped and did a quick visual check to make see if I could see anything wrong on the outside, but saw nothing. So I tried to kickstart the bike, and immidiately noticed there was almost no compression or resistance whatsoever. So upon getting the bike home and pulling off the cylinder head, this is what I found...

1000397k.jpg

1000401t.jpg

1000403o.jpg

Any help or insights would be greatly appreciated

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resize the pics, it will make it easier for us all to take a look at them.

from the looks of the crown of the piston and the head it looks like you had a bearing let loose. possibly your piston skirt shattered, ive seen damage like this from a shattered skirt before.

You need to get a new head or have it milled and cleaned up if possible.

your cylinder may be trashed also and will prolly need a replate.

looks like its time to rebuild your motor.

good luck

Dirty

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Good idea, I went ahead and resized them...hopefully that'll make it easier.

And thanks Dirty, any ideas as to why this happened, or is it just one of those things that gets more probable over time? I read somewhere that I should flush out my entire case for possible metal fragments, and I was wondering what the best way to do this would be.

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something that i missed at first. it looks like the top of your piston cracked/chipped is that on the exhaust side?

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That looks like a lower end bearing. What dirty said applies as well.

How much time do you have on your bike? Are you taking good care of the airfilter?

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I would say the chunk missing from the piston caused the damage. If it didn't spit the pieces out the exhaust immediately that damage would have happened in seconds.

I can't tell for sure but it looks like some errosion on the intake side of the piston possibly caused by detonation.

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Hard to say what started the sequence of events on that piston. The piece of piston missing looks like it fractured off not eaten by detonation.

It also looks like part of the top ring in that broken off area is missing? I would say that is the cause of the mechanical damage to the head and piston top and maybe the cause of lost compression. Check the cylinder wall for scoring.

How much time on this bike?

Is it possible that you were getting lots of piston slap prior to this happening? I'm just thinking if the piston was worn enough then the skirt fractured and that allowed the piston to tip into the exhaust port enough to break off that chunk of piston.

You'll likely need to split the cases if you find the skirt broken up or any evidence of contamination in the bottom end.

Useing a Wiseco piston or more frequent top ends with cast pistons will prevent the skirt from shattering.

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What did your plug look like? Was the electrode missing? I had one that looked similiar to that...and the electrode broke off and hammered in divots just like that...

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Well I had to work late today but found a little bit of time to pull off the cylinder in an attempt to get a good look at what was going on and what I found was that the only other damage to the piston was an extremely small crack/chip on the intake side, and that there are a few faint vertical marks on the inside of the cylinder.

Dirtymutt9-Yes, that chip is indeed on the exhaust side.

RCannon-I bought the bike towards the end of 07 and have been the only rider since. To be honest I am far from knowledgeable in the area of mechanics and have never replaced the piston, both from procrastination and having been away from home for several months, but do regularly check it for any visible signs of wear. Mistake I know. I clean my air filter regularly also.

CV4 and AV8R-Yeah I was kinda wondering if that chunk was the first to go and caused the damage on top.

BrandonCA- I went and checked my plug and the electrode was still there.

Any ideas as to what I should do next? And man this was my first post on here and am so suprised about the number of helpful people on here. Thanks again guys

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Actually this is more common than you think. I bet you find a small gouged area just above the exhaust post. Once it gets deep enough the ring/s catch on the downward stroke and you can see the results. Time for a big bore kit or replate if you have to stay at 250cc's.

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Actually this is more common than you think. I bet you find a small gouged area just above the exhaust post. Once it gets deep enough the ring/s catch on the downward stroke and you can see the results. Time for a big bore kit or replate if you have to stay at 250cc's.

There sure is. Also today I noticed a long gouge on the side of the piston. Will see about getting it bored out this weekend. Thanks

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The cylinder on the YZ's are nicosil coated, no bore for those things. Will have to have it -Recoated-..... I swear i saw a impression of a needle bearing on that piston, I also saw that piston breakage ???? make sure you check that lower rod bearing pull on the rod ( straight up and down) and make sure there is NO up/down play in it,that will verify(possible lower needle bearing) came out and was sucked up to the head. Pull the piston off too and check that upper rod bearing. Hope I'm not right, but boy there are perfect needle bearing indention on a couple places on that piston:banghead: Good luck

Techmc

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What was your jetting and weather conditions?

Looks like it may have ran hot and started a meltdown on the exhaust (aka the hot) side. Looks like spatter marks on the exhaust side of the piston crown.

My condolences. But on the bright side.... be glad it wasn't a 4T.

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The cylinder on the YZ's are nicosil coated, no bore for those things. Will have to have it -Recoated-..... I swear i saw a impression of a needle bearing on that piston, I also saw that piston breakage ???? make sure you check that lower rod bearing pull on the rod ( straight up and down) and make sure there is NO up/down play in it,that will verify(possible lower needle bearing) came out and was sucked up to the head. Pull the piston off too and check that upper rod bearing. Hope I'm not right, but boy there are perfect needle bearing indention on a couple places on that piston:banghead: Good luck

Techmc

And check the rod at ALL locations. Not just in the up position. This could have saved me a bunch!

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If you need a re-plate and I'm sure you do check out U.S. Chrome I've had a couple cylinders done by them with great results. My last one I sent I also had them do a new piston skirt coating they offer. It's not a "break-in" coating that comes on aftermarket pistons. So far it's held up real good during ice riding season.

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Something I just now noticed, in the first picture I believe the top ring is missing a large section based on what I could find online, and the second picture shows a long vertical gouge on the side of the piston.

1000404s.jpg

1000405q.jpg

The cylinder on the YZ's are nicosil coated, no bore for those things. Will have to have it -Recoated-..... I swear i saw a impression of a needle bearing on that piston, I also saw that piston breakage ???? make sure you check that lower rod bearing pull on the rod ( straight up and down) and make sure there is NO up/down play in it,that will verify(possible lower needle bearing) came out and was sucked up to the head. Pull the piston off too and check that upper rod bearing. Hope I'm not right, but boy there are perfect needle bearing indention on a couple places on that piston Good luck

Techmc

Lol wow that just goes to show how much I need to learn about this stuff. I have to wait until tomorrow to check the rod play, but I did check on the upper rod bearing and it was perfectly intact.

What was your jetting and weather conditions?

Looks like it may have ran hot and started a meltdown on the exhaust (aka the hot) side. Looks like spatter marks on the exhaust side of the piston crown.

My condolences. But on the bright side.... be glad it wasn't a 4T.

The jetting SEEMS to be fine, but again that's my pretty uneducated opinion. And the weather was about 65 degrees F so I'm kinda clueless now. :thumbsup:

And check the rod at ALL locations. Not just in the up position. This could have saved me a bunch!

I will def definitely be sure to do that in the morning, thanks for the tip.

If you need a re-plate and I'm sure you do check out U.S. Chrome I've had a couple cylinders done by them with great results. My last one I sent I also had them do a new piston skirt coating they offer. It's not a "break-in" coating that comes on aftermarket pistons. So far it's held up real good during ice riding season.

If you don't mind me asking, what was the more or less average price that you paid for each re-plate, and about how long did it take each time? Although I'm sure that can greatly vary by which location I use.

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My experience with US crome was less than stellar. Took a long time, 5 weeks I believe and the quality of the finish was acceptable, but not what I would rate high quality.

I have not used these guys but have heard many good things about them.

http://www.powersealusa.com/

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I sent my cylinder out to Millennium Technologies and I have to say that, other than having to chase the threads on several holes with a tap to clean them out, I am extremely pleased with the work they performed.

I paid 204.00 +s/h for my work and the darned thing came back looking so new I was astonished. The ports were all chamfered and the service was fast.

Sent it to them on a Tuesday, it arrived on Thursday, they had it back in my hands the next Thursday. 1 week from shipping to receiving rocks!

Be sure to ship them your replacement piston and rings so they know how much to coat it (longer it sits in solution, the more it gets coated, up to a point of diminishing returns)

You can also check to see if they have one in stock already to do a core exchange! they ship you the core, you put a sticker on your old cylinder, and return it in the same box. Works out to be like $225-ish? if I recall correctly.

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your skirt probably shattered...my head and top of piston looked exactly like this when my piston skirt shattered...u have to split the case and get all the metal shards out, and probably buy new crank bearings.

thats what i had to do, along with getting the cylinder plated and poishing the head with a wire wheel:P

good luck

btw i sent my cylinder to U.S. chrome and they did a FANTASTIC job.

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your skirt probably shattered...my head and top of piston looked exactly like this when my piston skirt shattered...u have to split the case and get all the metal shards out, and probably buy new crank bearings.

thats what i had to do, along with getting the cylinder plated and poishing the head with a wire wheel:P

good luck

btw i sent my cylinder to U.S. chrome and they did a FANTASTIC job.

If the skirt shattered he did a damn fine job with the old super glue to take the picture above...lol:thumbsup:

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