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yz250 topend rebuild...attempt myself?

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My bike needs a new top end and I was thinking about giving it a try myself. I have never done it before nor have I ever seen it done before. I have very little experience working on cars or bikes. I am a pretty smart guy and am very good at problem solving.

I would really love to know how to do this and it will save me some money and give me confidence to do just about anything else that would be needed on my bike.

Is this something I should try myself? How hard is it really?

By the way my bike is a 05' yz250

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The beauty of the 2 stroke bikes is their simplicity. Most anyone can do a top end on a 2 stroke. Get a manual read over the procedure. Lay out the tools, get a clean work space and tear into it. There shouldn't be any specialty tools required just a torque wrench. One of those pipe spring hooks helps alot in removing the pipe. Get a piston kit with the gaskets and you will need to drain your coolant system. The bore can be cleaned up with a scotchbrite pad. I would clean the carbon off of the combustion chamber and remove the gunk from the powervalve while youn are in there. I am no master mechanic but can pull off top ends rather easily both 2t and 4t.

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The hardest thing about the whole job is putting the little circlips in that hold the pin in the piston. Just be careful you do not fatigue or bend the little clips, and don't drop one into the bottom end either.

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its a very simple job to do if you just take your time and go step by step. The side of the piston will have a relief cut into it to make getting the C clips on and off. if you use a small screwdriver in this relief you can pry them out without damage but i highly reccomend new ones anyways. they should come with a new piston. When you get the cylinder and head off and your ready to take the piston off stuff a shop rag down around the connecting rod so if you do accidentally drop a cclip you dont have to go fishing around in your case for it. Also make sure everything is clean and dry around the area. you dont want to fill your case up with dirt. You have to drain your radiators but you can leave them in place(the lowest bolt on your waterpump is the drain). you must remove the tank. taking the subframe off makes things easier as well but its not needed.

jfgjr is right, there are no special tools required. the biggest thing to look out for is the locating pins that are in your piston ring groove. you need to make sure your rings are in correctly and that the gap in the ring lines up with this groove. ive seen people get this wrong and try to force the piston back into the cylinder and it never ends well.

when you go to reinstall your cylinder over your piston you can easily compress the rings by hand.

when the new stuff is in there will be a small breakin procedure but nothing like a new bike. you just have to be sure you seat the rings properly.

everything will be covered in detail in your manual.

good luck

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The hardest thing about the whole job is putting the little circlips in that hold the pin in the piston. Just be careful you do not fatigue or bend the little clips, and don't drop one into the bottom end either.

agreed, the clips are the hardest part, i learned on tt to work them in with a flat screwdriver, this is the easiest and fastest way i have found to do it.

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How did you manage to leave the rads on? I think I had to take mine off as well.....or assumed I did. The 97 needed them removed. Leaving them on would be really nice. I will try it next time.

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How did you manage to leave the rads on? I think I had to take mine off as well.....or assumed I did. The 97 needed them removed. Leaving them on would be really nice. I will try it next time.

Yes to the question should you rebuild this yourself. Go slow, use your manual and ask questions if your unsure of anything.

The best part is not the money you saved. There is something that happens inside once you get the bike back together and start it. The feeling is great.

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You can leave the rads on the steel framed YZ250s (02-04)... I've done it at least six times.

I haven't done it on my Al framed YZ yet so I can't comment...

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Definitely do it yourself. It's great to do your own plus you can ride it later that day with no waiting on the shop to get to it. Plus if by rare chance you snag a ring or drop a circlip into your case because you didn't throw a rag in there, you don’t have to drive to the service shop to yell at someone. You can just throw a wrench through your own garage window and still be riding an hour later.

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It never seemed like the radiators were in my way so I left them on. Just make sure the piston is all the way down when you take off the cylinder.

100_00951.jpg

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Thanks for the tip on leaving the rads on. This will shave at least 10 minutes from the job. That would have been nice when I did mine when it was 15 degrees.

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Thanks for the tip on leaving the rads on. This will shave at least 10 minutes from the job. That would have been nice when I did mine when it was 15 degrees.

Redneck just doesn't go outside in that kind of weather :thumbsup:

Seriously... the hardest part that I've found with rebuilding the top end is cleaning to carbon off of the PV... this was on the ktm though. I haven't done a top end on my yz, but i'm not at all worried about it after seeing how easy the ktm is.

If i can rebuild the top end of a bike... anyone can do it. I'm probably one of the worst mechanics on TT.

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Thanks for all the great feedback. You guys have definitely given me the confidence to do it myself!

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You guys on tt here have convinced me to have a go at doing my own top end rebuild, so i'm going to give it ago at it, i'm just waiting for parts to come in. i was just wondeirng how do you clean up the power valve ? And what with? . As i dont really want to muck around with the power vavles. And also best way to clean the carbon built up on the cylinder and the head.

Aaron

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Before you worry much about the pv, look at it. It might be in better shape than you think.

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