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yz125 my first rebuild

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Take apart the rear suspension and check all the bearings.

Check front and rear wheel bearings.

Check steering head bearings.

Check drained oil and the inside of the engine for metal flakes or chips. Chances are if it's rattling, something has gone wrong. You NEED to find what broke and all pieces or it can cause catastrophic problems later.

Check powervalve assembly. Make sure it is clean and functioning properly.

Inspect inner cylinder wall. It will probably need to be replated.

Replace piston and rings.

Inspect crankshaft and connecting rod. They will probably need to be replaced. (you can probably get the crank rebuilt with a new connecting rod kit.)

Replace crank bearings and oil seals.

Check all of the engine bearings, make sure they are running smooth and have no up/down play. Replace any that are bad.

Check all engine oil seals and replace any bad/brittle/cracked ones. Sometimes these come in a complete gasket kit, depends on the brand.

Inspect water pump shaft. If it has shallow grooves, you can probably polish them out with scotch brite and fine grit sandpaper and a powerdirll. If it has deep ones, it will need to be replaced.

Inspect transmission for bent/worn forks, gears missing teeth or any other damage.

Check reed assembly.

Re install all bolts and nuts to correct torque specs. This is especially important inside the engine to make sure no fasteners are loose enough to back out and destroy your motor, and to keep you from over tightening and pulling the threads out of your cases!

I'm probably forgetting something, but this should get you started:thumbsup:

I just finished this process on a 2001 YZ250 that I got as a project bike. I'll be breaking in the engine tomorrow:banana:

Have fun!

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how long is a piece of string?

It all depends on what you replace, and what tools you need.

At a minimum you'll need a new top end kit and all gaskets, thats about $150-$200.

You should at least do your crank bearings, and probably some other bearings too. Probably another $40?

Then you have to find out what's rattling and fix that, $?

You'll need some special tools, like a flywheel puller and clutch holder, total about $20 from RMATV

You may also need a case splitter and crank puller (although you can ghetto up these if you wish) $60 each from RMATV

Overall though, while it may cost a few hundred, once you get it all back together the thing will absolutely rip and you'll have piece of mind that nothing is going to blow up later causing catastrophic failure and $$$$$$$$

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wow... how much will this cost you reckon?

Think of it this way: once you do this, just about every wear point will be new so you practically have a new bike. Mechanically atleast.

I just did this to my 01 YZ 250. I replaced all the engine bearings $150 ish, including crank bearings. Get them at a local shop, not OEM (too much $$ for exact same bearing). The bearings will be cheaper still if you don't get them from an idiot distributor like I did... Had the crank rebuilt with japanese parts by Mr. Crankshaft (great guy) $170. New engine gasket kit $57, new engine oil seals $50 ish IIRC. Oil seals will probably be cheaper if you get them at the same place as your bearings and not the dealer like me... New front and rear wheel bearings $50 ish. Again, you could probably get the bearings and oil seals at a bearing place and spend less, I got Pivot works Kits before I knew this. New intake manifold $50 ish and a bunch of small parts $? and a new plug $6. I may have forgotten something, but I spent about $500

I rebuilt the linkage bearings myself. Just pull out the pins and if they aren't rusty you can clean them and re-install with grease. Swingarm bearings were good, so were shock and steering bearings. Fork seals were OK so they stayed. The PO had just had the cylinder replated at US chrome, and a new OEM piston and rings. That would have added probably around $300 ish if that needed to be done.

Yeah, it's not just a top end job. You could be looking at close to $1000 if everything is bad, also depending on the cost of parts where you live. But like I said, especially if you replace the parts with quality ones and don't cheap put, you'll have a practically new bike! You will also have something to do in your free time for a week or two, you'll know EVERYTHING about your bike, you'll know the condition of everything (no more I wonder if the PO did...?).Or you could just buy another used bike for around that much and not know what is wrong with it...

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I just got done a rebuild on my yz 125.... make sure to check you're transmission once before putting the cases together (tough to do, but its worth the struggle since it'll confirm to you its good) then again when the cases are together. I didn't on my yz, and found that out the hard way when I started it up and found first wasnt there. Idk if it was a specific issue with mine or if all yz 125 trannys are finicky but mine was a pain in the ass. Seemed like it worked fine then get it in the motor and it didn't at all. Beside that its easy, pay attention and it'll go great haha I didnt and paid for it.

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