Rode With No Coolant And Now My YZ400 Won't Start! HELP!

10 replies to this topic
  • bcaskey08

Posted November 06, 2013 - 05:50 PM


So after hours of searching over the FAQ and various threads on this site I have resorted to making a new thread. This is my first post on TT but I am quite familiar with forums as a whole so here it goes:


I recently bought a YZ400f with a 426 top end on it and I took it out to the desert and went on a group ride with some more experienced riders than myself. Needless to say the took me on one hell of a ride and I dumped my bike twice. The first time was a soft landing and the second time was a little harder but iI was uninjured in both. the problem is that on the second drop one of the lower coolant hoses came loose and started a slow leak. once I started riding again, the pressure built up and dumped all of my coolant out without me knowing. the bike kept running for a while, then i stalled it (let the clutch out too fast) it became harder and harder to start each time i shut it down (using the killswitch). we ended up bump starting it to get it back to camp (10 miles) then I put it on the trailer and went home.


The next day I tried to start it and nothing. I still have what feels like a lot of compression (the TDC lump is still hard to push through without using the decomp lever) so I changed the spark plug thinking that I fouled it when it was on its side but that diddnt fix the issue, so next I dropped it off at a local shop in Vista, CA to have the carb cleaned and re jetted since the previous owner had it set for 3000- 6000ft above sea level and I live at sea level.  So the shop cleaned the carb and rejetted it but they said it still wont start. I told the tech that it had overheated bad and he said that the piston rings were probably fried and it would be $600 to redo the top end.


What do you guys think? is that a reasonable assumption and if so is that a reasonable price? I'm new to riding so I'm struggling a little. Any help would be appreciated. Thanks!!

  • 707ktm

Posted November 06, 2013 - 05:59 PM


Overheating can do much more than just fry rings. Probably needs all new top end. 



  • theoriginalone

Posted November 06, 2013 - 06:06 PM


You would have to take off the engine to really see the damage best of luck :)

  • grayracer513

Posted November 07, 2013 - 07:23 AM


Could be a lot worse than $600. I've seen the heads start to melt between the exhaust valve seats when they're run with no coolant.  Figure a new or replated cylinder, piston, rings, gaskets, and probably at least two exhaust valves and seat refinishing. 

  • bcaskey08

Posted November 08, 2013 - 04:33 PM


Damn. That's what I was afraid you guys were going to say.

So if there is still a lot of compression does that mean that the rings are still intact?

Also the tech said that he doesn't do compression tests on one cylinders because it's only a test of how hard you can kick it over.

Is there a way to test to see if the rings are infact fried or not?

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

Posted November 08, 2013 - 05:01 PM


The only way is to take the engine apart, its not that hard, just take your time and everything will be fine, look at tutorials it shows it in a very detailed way :) best of luck

  • grayracer513

Posted November 08, 2013 - 10:00 PM


Is there a way to test to see if the rings are infact fried or not?


Yes.  You can have a leak down test done.  It will show you if it leaks, how much it leaks, and what's leaking.

  • bcaskey08

Posted November 14, 2013 - 07:08 PM


Yes. You can have a leak down test done. It will show you if it leaks, how much it leaks, and what's leaking.

So I called my local autozone, pep boys and oreilys auto parts store and nobody has a leak down tester. I did see this one online:


How much does it normally cost to have a leak down test done?

  • bcaskey08

Posted November 14, 2013 - 07:18 PM


Also I tried hill-starting it and I got it to run for 5 seconds then it cut off when I gave it gas which leads me to believe the piston isn't seized in place

  • capt justin

Posted November 14, 2013 - 07:22 PM


might not want to try to run it anymore until someone does a teardown, leakdown test , or at least a compression test.

  • bcaskey08

Posted November 15, 2013 - 12:15 PM


might not want to try to run it anymore until someone does a teardown, leakdown test , or at least a compression test.

That seem like good advice to me. I just wanted to make sure that I wasn't kicking it wrong and it really ran the whole time. I did all of the research about the "magic starting process" and I think I've got it down except for the part where the bike starts haha

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.