2004 yz450 rebuild problem

6 replies to this topic
  • 450GN

Posted July 14, 2007 - 07:51 PM


Well i have been in the process of fixing and putting back together my good friends 2004 yz450

well he had trans problems so i got new parts and put that back together...

didnt replace anything else other then the gaskets... well we got it fired up today and it started knocking a bit and sounded like piston slap or rod knocking in a car...

now we didnt put the timing chain black plastic tensior thing on the front side of the motor... i know that was a stupid idea but i couldnt get the cams in with that in the motor...

could that have been slappin?

ohh and then we got it started again and it ran for like 2 secs then just cut out and the kickstarter goes down 1/2 way and just LOCKS
but i took off the timing cover and turned the crank manually and it is fine...

any ideas what this could be.... please help

  • grayracer513

Posted July 14, 2007 - 08:13 PM


now we didnt put the timing chain black plastic tensior thing on the front side of the motor... i know that was a stupid idea but i couldnt get the cams in with that in the motor...

Take it back apart and install the chain guide like it's supposed to be installed. If it was interfering with the installation of the cam chain, the upper locating peg that sits in the cylinder was out of position. That piece HAS TO be there.

As far as the starter problem, I'm afraid you're going to have to open the rigt side up and figure it out.

  • 450GN

Posted July 14, 2007 - 09:06 PM


it seems very high in position... but there was a grove that the guide sits in and the round end of it fits perfect... but it was just too high up and rubbing on the cam and really had to push hard on the cam to get it to seat...

maybe i have to bend it away from the chain towards the top? it was locked in place

would this piece missing cause noise?

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  • grayracer513

Posted July 15, 2007 - 04:28 PM


The round end on the bottom is not the problem, it's the pegs at the level where the cylinder deck is that you have out of place. I don't know if it will cause noise or not, because I've never even considered leaving it out.

  • Jake92

Posted July 16, 2007 - 09:32 AM


Your trying to put it in upside down. Ive been there before.:thumbsup:

  • 450GN

Posted July 17, 2007 - 02:27 PM


yeah it wasnt upside down just bent to hell and would line up properly

it was making a nit of noise and has been sorted out for now...

now the bike feels like it has no compression... i took off the head to fix that... the valves are properly aligned... but there is a TON of air coming out the thick black hose on top of the cylinder head....

is the decompression messed up somehow?

  • DQDennis

Posted December 20, 2009 - 02:20 PM


I know this is an old tread, but....I have a 2004 WR450 with a similar issue.
I replaced my damaged cylinder head and installed new cylinder rings. It’s back together now, but it will not start. The electric starter is straining to turn the engine over. I also noticed air coming in and out of the crank case tube. When I installed the exhaust cam, I had to push the front timing guide down a bit, ¼”. I was wondering if that is normal? I triple checked the valve gaps. They are good. Any suggestions ideas are appreciated.

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