Replace Cam Chain Now?


4 replies to this topic
  • broncomoto

Posted August 01, 2009 - 10:12 AM

#1

It is my understanding that the cam chain should be replaced on the 2006 YZ450f motors as the one and only suggested/required motor maintenance issue. I purchased the bike new in March of 2006. I've ridden at the Novice level on this bike just about every weekend since then. I estimate about 150 hours of ride time on the stock motor. I regularly change the oil (AMSOIL). I've had not one problem, I'm just thinking it's time I do somthing.

First question:

Do I need to replace the cam chain - sight unseen?

If so, should I go ahead and decarbonize the valves?

Should I replace the top end?

Assuming yes to any or all of these questions, is my best bet to take the motor off the frame or can I do this with it still on the frame?

Bronco, Austin, TX

  • jasonbla

Posted August 01, 2009 - 11:08 AM

#2

replace the chain. I have a low hour 08 that stretched and the exhaust cam jumped three teeth. Its only a 15$ part. You can do it in the frame just fine, you'll need a flywheel puller and new gaskets. I think the total for parts on mine was 50$. pay attention to the specs for tightening the head bolts, yamaha does it a weird way. you tighten them to a specific ft-lbs then loosen and re-tighten then mark the bolts and go around one more turn. I went about 3/4 of a turn, they get pretty tight. I would replace it every year.

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  • grayracer513

Posted August 01, 2009 - 12:11 PM

#3

... pay attention to the specs for tightening the head bolts, yamaha does it a weird way. you tighten them to a specific ft-lbs then loosen and re-tighten then mark the bolts and go around one more turn. I went about 3/4 of a turn, they get pretty tight.

I'll bet they did. Spec is 1/2 turn after retorquing (180 degrees).

The timing chain is a two hour job if you haven't done one before. A little more if you take the time to find out what size shims your valves are wearing so that you can save a little time in the event they ever need shimming. It's cheap insurance, and can potentially prevent a fairly major disaster. Do it right in the frame. Here's a how-to thread. It was written for an '05 and earlier model, so the part about needing a torx bit to unbolt the stator plate does not apply to you.

http://www.thumperta...405#post3150405

Here's a little trick regarding setting the cams back in place and getting the timing right on the first try. (read and understand the whole post. the tip is in the 4th paragraph):

http://www.thumperta...845#post7467845

It would be wise to replace the tensioner, also.

Regarding the top end, a leak down test is the best way to determine if the job is needed. As to valves, read (answer 1):

http://www.thumperta...183#post8419183

The top end can be done in the frame or out. It's a little tricky to assemble in the frame, as the frame interferes with the removal of two of the head bolts. You'll know which two when you take it apart. OTOH, doing it on the bench requires something or someone to hold the engine while the head is torqued.

If you don't have a manual, you'll need one:

http://www.yamaha-mo...ice/manuals.jsp

  • broncomoto

Posted August 10, 2009 - 12:30 PM

#4

I'd like to check the valve clearance before I put it all back together. What is the spec on the valves (the manual is confusing to me).

Also, it is mentioned that when re-torquing the cam, go 1/2 turn past "the mark". Am I to understand that you torque to the specification ftlbs (how much is that in ftlbs) and then go another 1/2 turn?

  • grayracer513

Posted August 10, 2009 - 12:57 PM

#5

I'd like to check the valve clearance before I put it all back together. What is the spec on the valves (the manual is confusing to me).

Also, it is mentioned that when re-torquing the cam, go 1/2 turn past "the mark". Am I to understand that you torque to the specification ftlbs (how much is that in ftlbs) and then go another 1/2 turn?

The half turn past the mark is for HEAD BOLTS, not cam caps. Refer to manual page 4-28. I recommend 75 inch pounds (6.25 ft/lb) rather than the 86 specified. Torque them in 3 steps (45, 60, 75).

The valve specs are confusing? How? Refer to page 3-19. Specs are 0.10-0.15mm (.004-.006") for the intakes and 0.20-0.25mm (.008-.010") for the exhausts.





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