2004 Yz450f Cam chain drive gear help me!

8 replies to this topic
  • To-The-Wood

Posted September 26, 2007 - 03:47 PM


I took my bike to the local yamaha dealer because it was running like crap. They said all I need is probably a valve adjustment. When they took it apart they discovered that my cam chain was stretched and my bike was out of time. They said it wouldn't cost to much to fix because my valve clearance was still fine and nothing got bent when it went out of time.
Two days later they phoned me back and said that the drive gear that is attached to the crank shaft was damaged and that it would cost 1800.00 to fix.

My questions

Can the drive gear be changed or does the whole crank assembly have to be replaced?

Can I service the drive gear by just taking off the crank case cover?

Is this something I could handle myself?

How much should this cost to fix?

  • YZ250F_Rider

Posted September 26, 2007 - 03:52 PM


you need a new crank.

you can fix it yourself and the crank itself is like $250 or so (I think thats what I remember). But if you arent a serious backyard mechanic that tears engines apart and puts them back together again you will be better off letting the shop do it. It is a major effort. Try calling around and asking what other shops would charge to swap it out for you.

  • To-The-Wood

Posted September 26, 2007 - 03:56 PM


Is it hard to replace? Do I need any special tools other than a torque wrench?
Should I try to do it myself over winter?

Any idea how much this should cost to fix at a dealer shop?


  • YZ250F_Rider

Posted September 26, 2007 - 04:27 PM


The service manual is online at yamaha motorcycles, read it and become one with it to the point that you can state whats on the next page. then start asking questions about things you dont understand in it about tearing the engine down and putting it back together.

no clue on shop prices, but it will be mostly labor charges as it's a major teardown and rebuild. you can however pull the timing cover and the stator and see the gear at that point. You will be able to confirm at that point that the gear is damaged.

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  • grayracer513

Posted September 26, 2007 - 04:30 PM


To answer one of your base questions, no, the crankshaft cam chain sprocket is not an independently serviceable part; it's machined directly on the crank, and the only way that it can be replaced is by replacing at least the left side of the crank.

It is a considerable project to undertake, although if you have a good skill set, the only special tools you will need (unless you plan to have the crank rebuilt) is a flywheel puller.

However, I wonder if the sprocket is in fact worn or damaged badly enough to warrant such measures. You might want a second opinion. I've seen several of these that were, IMO, prematurely condemned.

  • YZ250F_Rider

Posted September 26, 2007 - 04:32 PM


I agree you at least want to get a look at the gear and see if a tooth is missing or the teeth are worn.

  • To-The-Wood

Posted September 26, 2007 - 04:34 PM


Thanks for info,
It's not what I wanted to hear, but at least I know my dealer is not trying rip me off.


  • YZ250F_Rider

Posted September 26, 2007 - 05:14 PM


If it's still in the shop, ask them to show you the crank gear. It will be obvious and they can point out the problems with it. Never think twice about getting them show you a problem.

  • To-The-Wood

Posted September 26, 2007 - 08:19 PM


Yep, That's exactly what I'm going to do this saturday. If anyone has any tips or info on parts, let me know.


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