No Compression After Fall YZ400F

5 replies to this topic
  • Motocrosschamp007

Posted July 04, 2011 - 06:19 PM



im new to this site and after searching around for the last two weeks i cant really find something which really resolvs my problem.

after riding for about an hour i dropped my bike on th left hand side while trying to get off...:ride: i then got back on and staqrted it for about 30 secs and let my cousin go for a when he got on the bike he did the exact same thing!! :thumbsup:

i picked up th bike strait away and trie to kick start it with absolutely no compression???

the bike has just been fully serviced and gaskets replac and the techs at yamaha state everything in the motor is running fine IE bottom end, top end valves, cams and everything..

im stumped.. what could it be? im thinking a stuck valve but how would i be able to fix that anyway? what else do you think it could b?

any help would be grand.. Thanks fellas

  • zlathim

Posted July 04, 2011 - 07:29 PM


Does your bike have a compression release lever on the handlebars?

If so, you might have a bent exhaust valve.

Your description doesn't really mention whether the bike was running when it was dropped, so it's just an idea. I may be wayoff base, but it was the first thing that came to mind.

Good luck.

  • Motocrosschamp007

Posted July 04, 2011 - 09:45 PM



Thanks for the suggestion. no, both times when the bike fell the engine was not running.

I do have a compression lever on the handle bar so i might have to chack the valve

but the first tim it dropped it started right away but the second time ,, no compression..

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

Posted July 05, 2011 - 03:14 AM


I'd have to suspect that something about when he fell bent or bound up something in the compression release system. That's where I'd start.

  • MANIAC998

Posted July 05, 2011 - 04:22 AM


My guess would be that compression release assembly too. Back in '98, I accidently pulled mine in when I reached for the clutch lever to fan it coming out of a corner. I immediately bent the exhaust valve! Hopefully, your cable is just corroded or routed improperly causing it to hang up. Maniac

  • Sebastian Pavich

Posted October 16, 2011 - 07:10 PM


the only way to find out man is pull the head and look at the valves. think about it, the motors is running untill the the lever is hit, thats what killes the motor, the lever pushes the exhuast valve down when the piston is coming up and makes contact, causing the bending of a valve. but u wont know for sure until u check it out.

Edited by Sebastian Pavich, October 17, 2011 - 06:59 PM.


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.