Changed piston out and now it won't FIRE

6 replies to this topic
  • craigroyse

Posted November 25, 2007 - 07:16 PM


Hello. I have a 2007 yz450f. I changed the piston, rings, and timing chain out today. Now my bike won't fire. Everything on the bike ran good before I tore it apart. I don't know why my bike won't fire. I checked to see if the plug was sparking, and it was. I tore the cams out and changed them around like 5 times because It is SO HARD TO FIND T.D.C.. My flywheel has like a " |-| | " on it. Looks like an " H " sideways and then a mark up and down. What I also did was took the plug out and stook my 1/4" extension on top of the piston and when the extension was at the highest point (piston at the highest point) The sideways H was turned clockwise almost out of view. Please help me find T.D.C.. Also, why wouldn't it be firing? AGAIN, MY BIKE RAN FINE BEFORE I TORE IT APART, JUST PUTTING A NEW PISTON IN FOR NEXT YEAR.

  • Kent Rathgeber

Posted November 25, 2007 - 07:21 PM


I know this is gonna sound stupid, but have you turned the gas on??

  • craigroyse

Posted November 25, 2007 - 07:23 PM


Yes, it had gas. I even took the jets out and made sure they weren't clogged up.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • rexbond007

Posted November 25, 2007 - 07:38 PM


did you check to see if you had spark, the spark plug coil wire might not be plug in all the way.

  • grayracer513

Posted November 25, 2007 - 07:55 PM


The marks look like this:

|-| |

<------ They move that way as the engine turns. The 3rd vertical mark "|" is TDC, not either edge of the "|-|". If you have had the flywheel off, verify that the "|" will line up at TDC. Of it will not, you may have the flywheel key out of place.

  • craigroyse

Posted November 26, 2007 - 05:19 AM


I do have spark. I will check the flywheel. There is a slot on the flywheel when you put it on that the woodruff key goes in so I don't understand how the flywheel can be off. But that is something that I will check.

  • craigroyse

Posted November 26, 2007 - 06:39 PM


I fixed the problem. I took the flywheel back off and put it back on. I didn't see any noticable difference that it was off. But it fixed the problem.

Related Content


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.