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A few weeks ago at Budds, bike lost all power then would not restart. Pulled the top end today and found this (pics below). I have a new piston ready to go in, and the cylinder looks fine. Can the head be re-used after some light dremel/sanding work? Is it toast? 
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Ouch! Did the spark plug break?
I'd buy a new head. That's just what I would do.
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Clean it up. Might gain a CC or 2 of volume but other than that it'll be fine.
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zehn wrote:If you want to try to salvage it, give these guys a ring.
https://www.millennium-tech.net/
^^^^ This right here or any other competent engine builder could clean that up and possibly offer you some options for a performance gain depending on what bike it is for. Have had much worse cleaned up like new many times over.
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Gotcha. Its an 03 CR125. All stock. Any idea vaguely how much it would cost to be professionally redone?
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My rough estimate would be ~$200-300 plus shipping. A quick look at the various parts sites shows that there aren't any OEM cylinder heads available.
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Take it and have the squish redone.. that can be fixed easily in a lathe, but last time I checked the cr head was cheap but here you go on 
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Either you took a flat blade screwdriver to the top of it or those perfect rectangular impregnations that resemble a needle bearing had some fun in there. I would be concerned about the trash in the crank over the head. Dings in the head can be sanded down and polished and be good to go. However you need to make sure nothing is in your crank.
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I rescued cylinders far worse off that that one. I was a journeyman machinist at the time so that helped. lol
Here is the basic procedure I used. If you don't have access to the machinery it won't help but if someone does this may give them a spark of an idea.
I screwed 3 pieces of steel round stock to the top of the head through the mount holes.
Then I secured the head down and machined the three posts so they would sit flat.
I flipped the head back over and held it down by the gasket surface.
I then put it on a jig grinder and matched the cylinder head shape and ground straight down until damage was gone.
Once the combustion chamber was clean I would run a hold down through the spark plug hole and remove my clamps from the gasket surfaces and machine an equal amount off the gasket surface.
I ran hundreds of hours on a head that was beat up worse than the one shown so it can be done.
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As suggested above, looks like needle rollers have been through there- check the big and little end bearings. Might be in for a full rebuild. Head can be salvaged best by a machinist taking the combustion chamber back and then machining the gasket surface accordingly. Also you can see by the piston that the engines been detonating. Get the machinist to address that or if you get a new head, run better gas from now on.
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You have a roller bearing pin that did the damage so you need to split the cases and see if it was a rod bearing or a wrist pin bearing failure, either way you got to pull it apart. Have the head milled and squish re-cut if you want to keep the head.
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Since you took piston off snd obviously didnt find the top end bearing is shot i bet. $100 and a bottle of cheap tequila that the bottom end bearing went south. The head is fine just clean it up.
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This! Even if it was the top end bearing, when the head and piston smash something together that hard it will compromise the connecting rod. If you reassemble the bike the rod will break EVERY. SINGLE. TIME (unless you ride like a total pu**y).
Time for a new rotating assembly. DO NOT USE A WISECO CRANK! FOR THE LOVE OF 2 STROKES, I REPEAT DO NOT USE A WISECO CRANK! OEM ONLY!!!!
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lol, so if he rides like a pussy his "rod" wont be compromised? killing me
Looks like a needle bearing, but having a hard time picturing, if its a lowe or upperr, how it would leave its home without the the end breaking off?
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The rest of the pieces are either in the crank or what went by the piston (scarred cyclinder) got banged around for a minute in combustion chamber and out the exhaust.
Piston is alluminum and so is the head. Pins are hardened steel. Doubt the crushing/impressions of the pins caused any dMage to the rod (pussy or not). However, the crank needs to be inspected for additional shrapnel.
What did you wrist pin bearing look like? Still in tact?
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I'm sure if the wrist pin bearing went bad he would have noticed it. Usually massive wear on the pin or the bearing would fall to pieces when the pin comes out to remove piston. I still say the lower rod bearing, or sabotage by way way of needle bearing through air filter 
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Just an fyi but if you are gonna replace, the 02 head is a little higher compression and bolts right on.
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Thanks for the advice guys. I've owned this bike since new and have actually never done a bottom end, so I think it's finally time to do a full rebuild. I don't see any bits of the needle bearing anywhere, so I agree it's probably down in the crank.
One of you mentioned the 02 head will fit. Any other years compatible? Seems like there are some choices on ebay.
