Yz450f dropped and won't start

27 replies to this topic
  • Crazyclown

Posted September 24, 2013 - 06:25 AM


I wiped on a jump and now my bike kicks over very hard and sometimes jams and won't fire up. If anybody knows what the issue might be id like to hear it.

  • grayracer513

Posted September 24, 2013 - 08:25 AM


Check your cam timing.

  • Crazyclown

Posted September 24, 2013 - 01:43 PM


Is it possible for it to mess up the timing by dropping the bike?

  • grayracer513

Posted September 24, 2013 - 03:49 PM


Under certain oddball circumstances, it could happen.


You have a problem with the bike, and the symptoms point to cam timing.  Ignore the crash part and work with the symptoms.

  • KTM_Pat

Posted September 24, 2013 - 04:55 PM


Dr. Grey...

  • Crazyclown

Posted September 24, 2013 - 06:29 PM


Ok, so How do I check the timing? Iv read some of the other posts about it but still not sure about how to do it.

  • Crazyclown

Posted September 24, 2013 - 07:01 PM


I checked and if I did it right, my timing is of, I found tdc the spark plug way and my mark lined up with the front line of the H. Does that sound right? And how do I change the timing chain?

  • grayracer513

Posted September 25, 2013 - 06:34 AM


To start with, what year is your 450? 


The timing mark you're looking at, the "H", is a couple of degrees before TDC (the "I"), but you're not looking in the right place.  The timing procedure depends on the year model to a degree, but in either case, the idea is to remove the cam cover and determine whether the cams are in the correct relation to the crank.  The TDC mark on the crank is lined up on the compression stroke, and then the marls on the cam sprocket are checked.


So again, what year model do you have?

  • Crazyclown

Posted September 25, 2013 - 07:14 AM


Ok, it's a 08. And I do have my valve cover off already. I'm not sure what position the cams are supposed to be.

  • grayracer513

Posted September 25, 2013 - 09:22 AM


You need a manual:




Nevertheless, on the cams, you will find two marks on the exhaust sprocket, and three on the intake.  With the flywheel lined up at the TDC ("I") mark, the cam lobes should be pointing up and out at an angle.  If they are pointing down and in, turn the engine one full turn forward so that they are pointing up.


The exhaust cam timing marks should be at 12:00 and 9:00 o'clock, roughly, with the 9:00 mark aligning with the surface of the head as shown.  The marks on the intake are marked with an E and an I because it's the same sprocket they used to use on the 400's and 426's.  The intake should sit with the E, the single dot, and the I at 9:00, 12:00, and 3:00, with the "I" on the cam aligned with the head surface. 


The cams won't align "perfectly" most of the time.  The question is this: If the timing mark was on the next tooth instead of the one it's on, would it be closer to lining up or not?


If you have to change it, or if you replace the cam chain, be EXTREMELY careful with the caps going back together.  NEVER force the caps down over the cams, or draw them down with the bolts.  They must be seated by hand and sit all the way down before the bolts are run down.  Oil the threads lightly, tighten in stages, and never exceed 7 ft/pounds (84 in/pounds).


Cam chain replacement:  http://www.thumperta...91#entry2520291

Attached Thumbnails

  • timing.png
  • torque.png

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  • Crazyclown

Posted September 25, 2013 - 04:35 PM


ImageUploadedByThumper Talk1380155634.257912.jpg ImageUploadedByThumper Talk1380155648.945643.jpg
So that's what i got, I'm lined up with the I and my one dot lines up good but the other one doesn't

  • Crazyclown

Posted September 25, 2013 - 04:39 PM


ImageUploadedByThumper Talk1380155986.612652.jpg
And that's not up and out.

  • yam 3

Posted September 26, 2013 - 06:09 AM


Cam chain looks kinked (1st pic middle of chain between cams)...probably a good time to replace it.


  • grayracer513

Posted September 26, 2013 - 06:41 AM


Yup.  The cam chain is toast, and the exhaust cam's way out.  That's why it's hard to kick; the auto decomp setup is fixed to the exhaust cam, so it's out of time too.


What happens is that the chain comes up off the crank with several of those kinks in it, and the tensioner isn't strong enough to push them back out straight.  Then, during a stall or a backfire on startup, or during a crash, the engine gets "bounced" backward a little ways, and that reverses the drive tension on the chain.  That in turn yanks all the kinks out on the normally slack side of the chain, creating a considerable amount of slack in the chain for which there is no correction, since the tensioner is held down by the load.  Then, the chain skips on one or both sprockets and there you have it.


If you haven't bent a valve (if you're complaining about a boat load of compression, you probably haven't), you should be able to fix this with no more than a new chain and a couple hours work.  You'll need a flywheel puller.

  • Crazyclown

Posted September 26, 2013 - 06:57 AM


So do I need to do anything with the decomp setup or is that just out of timing because my exhaust cam is turned?

Yea I figured out I need a flywheel puller, so what's the easiest way to get the nut off that's holding the flywheel? And I was trying to check if I bent a valve but couldn't really tell, so should I open the motor further and make sure I didn't bend any valves before putting it back together?

  • Crazyclown

Posted September 26, 2013 - 06:59 AM


Also I lv been reading a bunch of posts on here, and I read something about getting a different flywheel would help the bike from stalling as easy? Or did I read that all wrong?

  • grayracer513

Posted September 26, 2013 - 08:14 AM


The flywheel nut on the Gen2 engines ('06-'09) is easy.  There's a flat section on the puller threads of the flywheel that fits a 19mm open end. The crank/flywheel can be held with that while you use a 17mm to remove or tighten the nut.


Heavier flywheels will help with stalling to some extent.  They also improve the overall tractability to the engine at speeds below 4000 RPM, and help increase traction in the lower gears, all with no measurable performance loss.  IMO, you should use the heavier GYT-R "off-road" flywheel (+9 oz.) or an equivalent.  It should have been built with it in the first place.

  • Crazyclown

Posted September 26, 2013 - 10:14 AM


What's a good weight to go with for the flywheel?

  • grayracer513

Posted September 26, 2013 - 11:24 AM


Go back and read my post again.

  • Crazyclown

Posted September 26, 2013 - 10:02 PM


Sorry missed that lol. So is 11oz gonna b too heavy and I'm gonna loss power?

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