06 YZ450F won't kick over but not seized???


19 replies to this topic
  • SchmidtC194

Posted December 23, 2006 - 08:00 AM

#1

I was riding my 450 for about an hour. We stopped to take a break for 10-20 mins. When I got on it to ride again I tried roll starting like I sometimes do. It fired but didn't start. When I got to the bottom of the hill I tried kick starting it and it wouldn't kick over. It was like trying to start an older 450 with out the decompression release. After standing on the kick starter it would gradually turn the engine. It never fired back up though. got it home took the plug out and it kicked over fine. So I know the motor isn't locked up. I am thinking valves, or automatic decompress. Anybody ever heard of this????????

  • southerlin55

Posted December 23, 2006 - 08:08 AM

#2

You may have over heated your bike my 80 used to do that all the time..

  • SchmidtC194

Posted December 23, 2006 - 08:13 AM

#3

what happend to it when it overheated, and how did you fix it???

  • grayracer513

Posted December 23, 2006 - 09:43 AM

#4

Occasionally, the engine can come to an abrupt stop, like when it's stalled in gear, just as it hits the compression stroke. In this case, the cams may not have ever been turning slowly enough to allow the auto decompression flyweight to drop back and extend the decompression pin. When this happens, the pin is held back by the valve lifter, and the flyweight spring is not strong enough to extend it in opposition to the valve spring. To get past this, you either push it through to the next compression stroke, where it will work normally, or put the back in gear and back it up off of compression, which allows the AD mechanism to reset to its normal cranking speed mode.

If, however, you've done either of those things, and the engine still acts as if it has no compression release, one of two things may be wrong:

> The AD mechanism is jammed. (this is actually quite rare)

> The cam timing has slipped and is retarded. ( This causes the AD system to lift the exhaust valve too late)

Hopefully you just fouled a plug and got the engine stopped in an odd spot.

  • SchmidtC194

Posted December 23, 2006 - 12:43 PM

#5

Yeah I have tried all those things... I've been talking to some buddies and we are to the conclusion that I slipped a few teeth on my cam leaving the exausht valves closed. Cause it happend when I was roll starting down a hill. Maybe put to much of a strain on timing chain causing it to slip. Hopefully easy fix....

  • grayracer513

Posted December 23, 2006 - 01:58 PM

#6

Roll starting puts no unusual strain on the cam chain or any other engine component. None.

  • stroker101

Posted December 24, 2006 - 09:34 AM

#7

my 06' yz450f does this on occassion. what i do is just keep pressure on the kick starter untill the piston passes tdc on the compression stroke.

good tip grayracer513 on putting the tranny in gear and rocking the engine. i'll try that next time "it" happens

  • PK

Posted December 24, 2006 - 11:57 AM

#8

If you pulled the plug and kicked it through, it should have reset the compression release. Since it doesn't sound like it did, you should pull the valve cover and take a look at the compression release mechanism and you can check your valve timing in 5 minutes while your valve cover is off. You'll have an idea of what your dealing with after that.

  • SchmidtC194

Posted December 24, 2006 - 05:20 PM

#9

Thanks I will try that...

  • ____Kurt____

Posted December 25, 2006 - 09:05 AM

#10

that must be a scary situation, i hate it when something happens and you out riding.
hopefully the 07's don't do this and if they do not as much

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • live4speed

Posted January 25, 2007 - 10:09 AM

#11

this may sound stupid and obvious...but did you remember to pull the hot-start? is the engine still refusing to fire?

  • toombstone

Posted February 09, 2007 - 07:04 PM

#12

what ever happened? my 03 just did this and I really don't want to pull the head to find out what it is.

  • youngr24

Posted February 09, 2007 - 09:09 PM

#13

It is your cam chain. same thing happened to me. Your cam chain has jumped time so you decompresion in not in the right spot so you can't kick it though but once it falls through it feels like it will start but does the same thing again. Replace the cam chain and reset everthing to top dead center and the bike will fire right up. but replace the cam chain it will jump again trust me.

RY

  • ridder112

Posted July 09, 2012 - 08:36 PM

#14

my 2007 yz450f does that i with i was riding it and it stalled and i tried to kick it over and it would just not move so i was like f%#k its seized but then i held my foot there with all my body weight on it and it dropped down like normal but stopped dead right before the foot peg and thats all i get idk whats wrong HELPPPP!

  • grayracer513

Posted July 10, 2012 - 06:39 AM

#15

Sounds like cam timing. Check it. If you find it off, replace the chain AND the tensioner.

  • ridder112

Posted July 10, 2012 - 06:35 PM

#16

also ill put it in gear and hold the clutch and roll it back wards it stops dead

  • Yamaryder29

Posted August 27, 2012 - 07:21 AM

#17

Occasionally, the engine can come to an abrupt stop, like when it's stalled in gear, just as it hits the compression stroke. In this case, the cams may not have ever been turning slowly enough to allow the auto decompression flyweight to drop back and extend the decompression pin. When this happens, the pin is held back by the valve lifter, and the flyweight spring is not strong enough to extend it in opposition to the valve spring. To get past this, you either push it through to the next compression stroke, where it will work normally, or put the back in gear and back it up off of compression, which allows the AD mechanism to reset to its normal cranking speed mode.

This is interesting. I had it happen a few times when i had my yz426 and its happened about 2 or 3 times with my 08 yz450f. With both bikes and was always while stalling in gear and the first couple times I though I seized my bike up, but this makes complete sense. Thanks Gray

  • grayracer513

Posted August 27, 2012 - 08:25 AM

#18

This is interesting. I had it happen a few times when i had my yz426 and its happened about 2 or 3 times with my 08 yz450f. With both bikes and was always while stalling in gear and the first couple times I though I seized my bike up, but this makes complete sense. Thanks Gray


It only makes sense on a 426 if someone added automatic decompression to it.

  • Yamaryder29

Posted August 27, 2012 - 08:32 AM

#19

It only makes sense on a 426 if someone added automatic decompression to it.

I forgot to mention the 426 had a auto decompression hotcam.

  • grayracer513

Posted August 27, 2012 - 08:35 AM

#20

I forgot to mention the 426 had a auto decompression hotcam.


Figured as much, but just wanted to clear that up.





Related Content

Forums
Photo

05 yz450f not fast enough by RedeyeYZ


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies
Forums
Photo

YZ450FX OR YZ450F by MESSMAKER


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies
Forums
Photo

Should I buy this bike? help....... by Numsa Hul


Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies
Forums
Photo

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride


Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies
Wiki
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info


Articles
  • 0 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.