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timing chain? cam? forks?

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i have a 04 yz250f, i'm a car mechanic and see nissan maximas with over 200 links in the timing chain, and 19 more valves than my bike go over 300k miles. ford mustangs and pickups with dohc and 27 more valves and valve springs and just as many links in the chain go over 250k miles, all with original hydraulic tentioners and guides. why do we have to do timing chains so frequently? :D

Also i would like to know what the pros and cons of the hotcams would be for my bike?(besides shortened timing chain and valvetrain life) or what the best overall mods are for power and handling. best exhaust? high comp piston?chassis/unsprung weight loss?

Can anyone please tell me which type of forks are on my bike. its stock. id like to service them myself, but dont know if its cartridge or dual chamber or...?

thanks in advance, all input welcome!

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These are racing machines, not cars. They are high performance and are not made to go for a million miles. The timing chains are very light and small and get spun at high RPM's. If you run it too long and let the timing chain stretch too much it will ruin the sprocket on the end of the crank and you will have to replace the crank. It suddenly turns from a $20 job to a $300 job.

Hotcams do give nice power gains, about the same as an aftermarket exhaust. The nice thing about them is they are cheaper than an aftermarket exhaust, and you can't destroy them in a crash. The other nice thing is that they are a pretty mild profile and do not require any other changes to the valve train, and do not add much if any added stress to the valve train. I personally have run stage 2 hotcams in my last two YZ250F's and have never experienced shortened valve life, nor have I heard of many people having valve issues with them. Some of the more aggressive aftermarket cams require stiffer valve springs and can sometimes shorten valve life.

If I remember correctly, 04 had cartridge forks. The original owner's manual is the best tool you can get.

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what kj said.

basically, you've not worked on a car motor that idles at 2000 rpm and makes max hp at 10,800 have you? no. redline at 13,500? no.

produces 140hp per liter in stock form? no. (that's equal to 840 for the new corvette - yeah keep dreamin)

you have a 1/8th version of a F1 motor. treat it as such.

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I have a lot of people ask me the same question about these engines. That is a great analogy SUnruh. I think I will use that. (If you dont mind.) :D

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It suddenly turns from a $20 job to a $300 job.

That is not really accurate. Best case scenario is not a $20 job and worse case scenario is way more than $300. :D

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We don't want to price shock the guy out of servicing his bike:

04 yz250f camshaft chain $18.41, crankshaft assembly $271.76, kj seems pretty right on.

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The forks on all YZ/YZF models back to at least '95 are cartridge forks. That is, there is a damper cartridge assembly within the fork that does the rebound and some of the compression damping, separate from the main tubes. What the '04 and earlier forks are not is a twin chamber fork with the oil supply for the damper cartridge separated from that of the main tubes, and sealed away from air. The '05 and up models had those. The '04 and earlier are "open bath, circulating cartridge forks".

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I know you guys that have posted are all right about preventative maintenance and have posted some insightful info. But I've never heard of one failure due to a yz timing chain. I'm not saying your not right but even back to 01 on this website i don't remember alot. Personally I've never replaced mine, mainly due to lazyness.

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We don't want to price shock the guy out of servicing his bike:

04 yz250f camshaft chain $18.41, crankshaft assembly $271.76, kj seems pretty right on.

All I am saying is if the cam chain fails, the repair cost will [most likely] be a lot more than $271.76. I am glad to hear cam chain failures are rare on the WRFs. :D

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well put everone and thanks for the great info. im still unclear on the forks though if anyone can help me clarify i'd greatly appreciate it. as for the cams did you do both or one and if so which one? and in conjunction with exhaust what do you think?

as for the corvette thing, i own one. for sure its not the new 640hp one, but the only one that never had a pushrod motor was the zr1s in the 90s which were dohc. even the new 500 and 600 hp motors are pushrod, 2 valves per cyl. my hats off to those engineers, and mine gets 30mpg highway.

that f1 analogy really gets the point accross, i like it! well put, thanks for all the quick replys.

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I know you guys that have posted are all right about preventative maintenance and have posted some insightful info. But I've never heard of one failure due to a yz timing chain. I'm not saying your not right but even back to 01 on this website i don't remember alot. Personally I've never replaced mine, mainly due to lazyness.

The cam chain itself rarely breaks on these bikes, but it does stretch quite badly. If run for too long after stretching, it will destroy the sprocket on the crank. If you catch it at this point it will be a $300 fix, plus labor to slit the cases. If you continue to run it like this it will skip timing and destroy your engine, now it can easily be over $900 plus labor. Personally I just change the timing chain when I change pistons, every 50 hours of riding. Keeps the headaches to a minimum.

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I know you guys that have posted are all right about preventative maintenance and have posted some insightful info. But I've never heard of one failure due to a yz timing chain. I'm not saying your not right but even back to 01 on this website i don't remember alot. Personally I've never replaced mine, mainly due to lazyness.

Here is what happens if you never replace the timing chain. This is my bike an 03 YZF that I bought second hand. The teeth are worn that thin and stretched that much that the bearing will not come off the crank with out a sledge hammer! They are also starting to hook over like a worn rear sprocket, and we all know what happens to those! Change it, its cheap insurance. All is not lost though as I now have a 3mm stroker crank in mine! :D

PA170221.jpg

PA170220.jpg

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is that sprocket crankshaft material or aluminum? and those pics alone are all the convincing I need to change the chain frequently. how bout the guides what do you guys say wbout them? do they get replaced with a new chain or just when they show signs of wear?

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is that sprocket crankshaft material or aluminum? and those pics alone are all the convincing I need to change the chain frequently. how bout the guides what do you guys say wbout them? do they get replaced with a new chain or just when they show signs of wear?

That sprocket on the crank is machined into the crank, it's hardened steel.

And it is important to change the camchain frequently otherwise you WILL ruin the crank sprocket.

The guides/dampeners don't really seem to wear so chances are they will be fine.

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i am getting ready to the timing chain on my 04 wr. has anyone done this and if so what tool will i need?

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i am getting ready to the timing chain on my 04 wr. has anyone done this and if so what tool will i need?

You will need a flywheel puller, trust me I've tried everything and the flywheel puller was the only thing thing that worked.

It's a pretty easy task, just take the cam cover off, and the stator cover (remember to drain the oil beforehand), remove the flywheel, camchain tensioner, cam caps, cams, rear camchain dampener (from memory i think it got in the way) and swap the chain with the new one.

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