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My New 2003 yz125 Project Bike.

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Hey guys so I've been looking for a yz125 project bike for a while now. I finally found this yz125 project bike the guy claims it needs a new top end but you never know until you open it up. This will be my first project bike ever. I've never done a top end before or really open a engine but I've been reading and learning about yz125 2strokes. Also the guys has extras coming with the bike. He has a new top end kit, 3 extra radiators, new gas tank plastic, the stock cylinder and the new one on the bike. I bought the bike for $500 I think its a pretty good deal with all the extras. I will be posting pictures of me working on the bike. Beware its probably going to take a while to get this bike running. Here is what the bike looks like right now. Let me know if you guys have any tips for me.

 

 

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Looks like a very good deal for $500.00

Tips; fuel,air, and spark are the major requirements.

In my experience when the top end is worn out and sufficient compression is lost, they can still be push started for a short time before a tear down is required.

 Do the `extras` include a repair manual? If not, then that is where you should spend your first $60.00

 

Please do post pictures of your project progression, that is always cool, but remember you might find better answers to questions in the bike specific portion of TT.

 

Congratulations

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Hey guys so I've been looking for a yz125 project bike for a while now. I finally found this yz125 project bike the guy claims it needs a new top end but you never know until you open it up. This will be my first project bike ever. I've never done a top end before or really open a engine but I've been reading and learning about yz125 2strokes. Also the guys has extras coming with the bike. He has a new top end kit, 3 extra radiators, new gas tank plastic, the stock cylinder and the new one on the bike. I bought the bike for $500 I think its a pretty good deal with all the extras. I will be posting pictures of me working on the bike. Beware its probably going to take a while to get this bike running. Here is what the bike looks like right now. Let me know if you guys have any tips for me.

Restyle kit.

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Thankyou. I will probably download a manual online. But I figured I can sell 2 of the radiators for $50 a piece. And Spend it on parts. First thing I'm going to do is take off the back subframe,plastics,carb and gas tank. I don't know if I will take the engine off or just take of the piston and see if the crank needs a new bearing. I hope I don't have to buy a bottom end but you never know.

Edited by Dirtshark808

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Its not seized. but he said the piston went out so I don't know if he scratched the cylinder wall. Luckily he has 2 cylinders so if one is bad I'll use the other one. But I have to measure it first. Also I might just fix it and resell for a profit. But If I decide to keep it. I will for sure get new plastics. 

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Pistons and rings DO just go out, meaning they need to be replaced sometimes. I`m no expert, but this much I do know, and feel comfortable making the statement that a re-ring or piston and ring replacement is the one `major` (if you want to call it that) thing a 2 stroke will require.

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Definitely a good deal for $500. Doesn't looked clapped out, and looks awesome for $500. If I saw a bike for that, I'd pick it up there and then.

Good luck on the rebuild, and if you have the money, I would just replace the bottom end too for piece of mind.

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Hey guys started working on the bike today. I Took the Radiators/Seat/Tank/Plastics/Pipe and exaust/ Head and cylinder head. Here are some pictures.

 

The piston looks bad. The ring is stuck and the cylinder is a little messed up. I think the cylinder coating came off. I took the piston off to look at the bottom end to see if it moved or needed new barings and it did not. The only thing is the plastics on the bottom end pieces broke off I'm posting pictures of it tell me what you think. I don't know if I need to replace the bottom end. I took all the plastic pieces off they where on the top of the bottom end. I don't wanna put a new top end and then it breaks again. So tell me what you think.

 

 

 

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Also the guy gave me a fmf exhaust with the bike. I'm going to order a top end kit. But only until I know I don't have to replace the bottom end. I'm going to show a mechanic the pictures and see what he thinks. Any feed back will help! :D

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Thats the piston. It had some weird bump on top of it. Just wan't to point out this is my first top end rebuilt. Or project bike so any feed back will help me! :D

.jpg

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Dame that cyl is F'ed up. The crank have play in it?

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That piston looks roached and I'd be concerened about the broken missing part of the crank stuffer.

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That piston looks roached and I'd be concerened about the broken missing part of the crank stuffer.

Looks like it melted from lack of oil. I'm starting to think that's a common prob with the yz cranks. I went hot rods on my 250

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That bump on the piston may have been a "hot spot." Replace it. Looks like the cylinder has seen better days. Rebore/replate or replace it. How's the head? That plastic on the crank, (forgot what it is called, webbing? damper? buffer?) is concerning. Consider pulling the engine, split the cases and replace it. While the cases are split go ahead and have some fun inspecting transmission, bearings etc. Something caused that engine to do that. (Carbaration issues?)Enjoy the bike. Those yzs are great and 500 dollars is a super deal.

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If you plan on rebuilding your old crank I suggest you buy some metal or nylon crank stuffers Instead of the orginal plastic ones

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