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First topend rebuild. Questions and concerns.

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Hey guys this is my first topend teardown on my 2000 YZ250 and could use some pointers.

First questions, how to i remove the push rod under the power valve housing? It looks like i should be able to just remove the bolt that holds the top link but it's very tight. Second qustion, do i need to remove the radiator to pull the cylider?

First concern: When i removed the cylinder head, i noticed some coolant on top of the piston. The coolant was confirmed when i pulled the exhaust off of the cylider and it coolant ran out. Is this caused by a bad cylinder head gasket? Should i not worry about it since im replacing the topend? Second concern: When i pulled the spark plug, it was wet with fuel and black. The clamp on the carb to airbox hose was loose. Are these related? Do i need to pull the carb?

Thanks for any help fellas.

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Are you refering to number 36 on this link???

http://shop.thumpertalk.com/oem.asp?partcategory=36461&manufacturer=6&category=3&year=2000&model=962

If so, then you have to loosen alen nut 37 first in order to get out this bolt. All the pieces will then slide out. Be carefull, I believe you are supposed to use a key when loosening the nuts on the end of the bolt (part 36) to prevent undo stress being applied to the shaft and valves. There should be washer/key to prevent the rod from turning while loosening the bolt.

http://shop.thumpertalk.com/oem.asp?partcategory=36462&manufacturer=6&category=3&year=2000&model=962

(Part number 23 on link above is the pin to prevent the rod from turn while loosening bolt.)

I just had the cyl. off of my 06 yz and it didn't require taking off the rads. That being said, I later took them off and used the opportunity to clean and flush them out.

In regards to the antifreeze on the piston, is it possible you didn't drain out the antifreeze in the cyl. before taking off the head. If that is the case, then it was residue antifreeze that was in the head still. I would think if it was leaking bad into your piston, you would have noticed it when last running. Definitely replace the o-rings/gaskets when you put it back together. I would also check to see if any seeped past your rings and down into your crank. You may want to deal with that soon, to protect your bottom end from the anti-freeze.

In regards to the carb boot. If the boot was loose enough that air was coming in it would have made it leaner and possibly let in dirt to your carb and thus engine. Leaner would mean that your plug was not wet or black, but white. Black and wet is an indication of it running rich. I would take the carb off while you have the cyl. off and then you can check your jetting and clean it, making it ready for the season. Also, if you are rich, then you will want to know where you are at so the experts and the information here in the forums can give you an idea of where you need to go.

Do you have a manual?? I find them incredibly helpful. I am sure other's will post up too.

The Bug

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Great post Carver!!!! Pictures paint a 1000 words, the book says more!:thumbsup:

The Bug

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Hey guys this is my first topend teardown on my 2000 YZ250 and could use some pointers.

First questions, how to i remove the push rod under the power valve housing? It looks like i should be able to just remove the bolt that holds the top link but it's very tight. Second qustion, do i need to remove the radiator to pull the cylider?

First concern: When i removed the cylinder head, i noticed some coolant on top of the piston. The coolant was confirmed when i pulled the exhaust off of the cylider and it coolant ran out. Is this caused by a bad cylinder head gasket? Should i not worry about it since im replacing the topend? Second concern: When i pulled the spark plug, it was wet with fuel and black. The clamp on the carb to airbox hose was loose. Are these related? Do i need to pull the carb?

Thanks for any help fellas.

+1. it sure is handy to have baseline jetting info when it is together. So writing it all down now can save a lot of time and grief later.

DO NOT hammer the wrist pin out of the piston. Either carefully find and remove the burrs, or use a pin pusher. Otherwise you will end up with a bent rod.

If you had an air/dirt leak, you cylinder plating may be scored or otherwise damaged. Check it really carefully in good light. Better to get that resolved if necessary before reassembly than put it back together and have it grenade halfway through the season. Now would also be the time to check rod play and that sort of thing.

Be very careful and check everything, use all new gaskets and seals, o'rings, etc. And then you won't need to go back in for a while.

Care pays off. Reusing questionable parts cost more later. I hate rework. Do it right the first time and it comes out a lot cheaper. And you then have more time for riding!

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Got the piston out with ease. Cylinder looks and feels very smooth. No scoring or scratches. I will measure all crankshaft and cylinder tolerances while it's torn apart. I checked the reeds but they look brand new. Should i replace them anyways or just leave them? Do i need to do anything with the power valve? I pulled the carb as per your recommendation, besides from cleaning and setting float level, what information should i get from the carb to fix the running rich problem? I do have a manual for the bike.

Thanks

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Get all jetting specs. Don't forget needle and pilot screw adjustments. That way, you know what you have.

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I take my radiators off when doing a top end because I think its easier pulling the cylinder down over the new piston. Most people say to replace the reeds, I have v-force 2 reeds. I haven't replaced them for years, and they still look brand new.

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When coolant leaks into the cylinder of a running engine it will wash the top of the piston off. If the piston top has a brown to black top, it likely just leaked in when you pulled the head.....if it looks clean, suspect a leak.

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