06 yz450f kick start froze after backfire


9 replies to this topic
  • tazman450f

Posted June 05, 2009 - 06:06 AM

#1

Hi everyone. 1st post to the forum. I know this topic has been dealt with before but couldn't find the sequence for dismantling to find out exactly what is wrong. What needs to come off? What is the specific order of removing things? Does the engine have to come off the bike? I have the manual but under the Kick Axel and Shift Shaft section it says refer to Oil Pump section which says refer to Clutch section which say refer to.... Thanks for any help.

  • grayracer513

Posted June 05, 2009 - 06:38 AM

#2

On page 4-66 of the oil pump section, which you were referred to, it says to remove the clutch cover and right crankcase cover, referring you to the oil filter...crankcase cover section of page 4-56. RTFM.

But no, you don't need to pull the engine, just the crankcase cover. You'll need to drain oil and coolant. Look behind the clutch for some broken gears, also.

  • tazman450f

Posted June 05, 2009 - 11:43 PM

#3

Thanks gray. I'm going to pull the cover today and try to find the cause. Just like in previous posts I discovered I can rock the bike in gear and am then able to push the kick starter by hand. I don't get a full stroke but it definitely moves through at least the exhaust stroke cause I get air pressure through the can....but it locks up again. I'll try to post pics if I discover anything amiss.

  • grayracer513

Posted June 06, 2009 - 07:41 AM

#4

You might also want to take a look at the cam timing. If the chain's bad, and it skipped on the exhaust cam, you may actually be experiencing a lack of decompression.

  • weedhopper

Posted June 07, 2009 - 08:14 AM

#5

You might also want to take a look at the cam timing. If the chain's bad, and it skipped on the exhaust cam, you may actually be experiencing a lack of decompression.

Yep that happened to me a couple weeks ago. The cam chain was junk and the exhaust cam slipped by two teeth. I couldn't budge the kick starter. I would pull the valve cover and check that before taking anything else apart.

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  • tazman450f

Posted June 08, 2009 - 02:59 AM

#6

Yep that happened to me a couple weeks ago. The cam chain was junk and the exhaust cam slipped by two teeth. I couldn't budge the kick starter. I would pull the valve cover and check that before taking anything else apart.


So weedhopper, what did you end up replacing? Anything else get damaged?
I pulled the crankcase cover yesterday but didn't see anything. The kick axel seems to wobble a bit but I haven't disassembled it enough to remove it. Maybe today.

  • weedhopper

Posted June 09, 2009 - 07:06 PM

#7

So weedhopper, what did you end up replacing? Anything else get damaged?
I pulled the crankcase cover yesterday but didn't see anything. The kick axel seems to wobble a bit but I haven't disassembled it enough to remove it. Maybe today.

I just threw in a new cam chain and made sure that my tensioner was functioning properly. Luckily it only slipped a couple teeth and it didn't smash a valve or anything. I'm still puzzled as to why it happened. The bike is an 07 with few hours on it.

  • tazman450f

Posted June 11, 2009 - 05:01 AM

#8

I removed the clutch and pulled the kickstart assembly out...no visible damage. Next I pulled the valve cover...timing chain and cams ok. When I tried to set at TDC the cam marks line up but the timing mark on the crank doesn't. I can only rotate the crank so far before it locks up. I can move it back in the opposite direction and once again it locks up. Any ideas? Suggestions?
My next thought is to remove one of the cams then rotate the crank to the timing mark then replace cam, line up timing marks reinstall timing chain then see if I can rotate the crank through an entire stroke without it locking up.
Good idea? I'm thinking that maybe the timing chain jumped a tooth or 2. As I think I mentioned before, the bike was not running when it locked up. If the crank jump a tooth or 2 because of wear wouldn't that mean a rebuild is necessary even tho there is no damage?
Do you think parting out is a good idea? I got a smokin deal on it $2500,but have only ridden it 6 times. If I'm looking at $1500 + to fix:shocked:
What kind of $ would parting out bring?

Thanks

  • grayracer513

Posted June 11, 2009 - 07:44 AM

#9

I removed the clutch and pulled the kickstart assembly out...no visible damage. Next I pulled the valve cover...timing chain and cams ok. When I tried to set at TDC the cam marks line up but the timing mark on the crank doesn't. I can only rotate the crank so far before it locks up. I can move it back in the opposite direction and once again it locks up. Any ideas? Suggestions?
My next thought is to remove one of the cams then rotate the crank to the timing mark then replace cam, line up timing marks reinstall timing chain then see if I can rotate the crank through an entire stroke without it locking up.

If the TDC mark is not aligned when the cam timing marks are, then it's out of time. Disconnect the timing chain by removing the intake cam. You may or may not be able to walk the chain around the sprockets with the cams laying in the saddles with the caps off.

Carefully examine the chain for any stiffness in links, and reject it if you find any at all.

If it has the resistance to turn over after the cams fell out of time, it may be because the valves have struck the piston. Carefully check the valve clearances. Bent valves will show up as a valve with too much clearance.

  • tazman450f

Posted July 23, 2009 - 03:15 AM

#10

Sorry about the long delay on the update. Went on vacation yada, yada, yada....and just plain forgot:bonk:

Anyway, I pulled the cam cover off and sure enough, the timing was WAY off.
I removed the tensioner and was able to line up the cams WITHOUT removing the chain....major chain stretch! Once everything was lined up I was able to get a full stroke on the kickstarter. I bought a new timing chain, installed and haven't had a problem since :worthy: I've been to several tracks, done some dune riding and trail riding with NO problems.

I was fortunate to have this occur when the bike wasn't running. I can see how this would cause some major damage if the bike had been running:(

Moral of the story.... if you have this happen to you and can't figure out why it happened...REPLACE THE TIMING CHAIN!!! The tensioner should keep the chain from slipping when the chain is good, but may not be able to when the chain has stretched. A new chain was around $20!!!





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