New Bike Bad Engine

12 replies to this topic
  • deckdog66

Posted March 08, 2015 - 02:41 PM


Hi all. Trying to help a friend figure out his moto issues. the bike is a 2014 YZ450F with maybe 30hrs. The friend told me the engine won't kick start or pop start. when it did run, it blew oil out the breather hose. The first thing I did was put the motor on TDC and perform an audible leak down test. Intake was tight. Exhaust was tight. Crankcase leaking air badly. In light of the combination of the blow by symptoms and the failed leak down test, I told him his rings were bad and a top end tear down to confirm, and probable top end rebuild were in order. I also told him to get a second opinion. I just think it is weird for such a new and high quality machine to have issues like these so soon after rolling off the dealer floor. I was also thinking of a broken ring? Does anyone have any other ideas or can anyone confirm my thoughts? Thanks.

  • grayracer513

Posted March 08, 2015 - 06:17 PM


The thing that kills most of them is overheating. 

  • Monk

Posted March 08, 2015 - 06:42 PM


A lot of abuse can happen in 30hrs...

  • deckdog66

Posted March 09, 2015 - 05:15 PM


Yeah. Overheating would do it. This bike is ridden on dunes a lot which will make a bike run hotter and leaner too. Might have cooked the piston.

  • dirtbeater

Posted March 09, 2015 - 06:34 PM


Poor maintenance would not help anything either....

  • boegey

Posted March 10, 2015 - 01:17 AM


Just a quick question don't want to steal the thread but I was riding the other weekend and was going up this &%$#@! of a hill and it was so steep and was such loose dirt to the point where we had to walk along side our bikes rather than riding them to get some traction the bike overheated like three times because it was stuck on ruts in loose dirt whenever fluid started coming from the overflow I killed it and waited for it to cool down before starting again this is the first time it has ever overheated its a 2014 yz450f with 18 hours on it I didn't think it would have done any damage but I'm now freaking out should I be worried??

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  • deckdog66

Posted March 10, 2015 - 03:37 AM


Sounds like you did the right thing by shutting down. I would think the bike is fine unless you notice it does not run as well. I would keep an eye on the coolant level though.

  • dirtbeater

Posted March 10, 2015 - 04:45 AM


I had an 06 wr 250 that I boiled dry. We were a few miles from camp. I just rode it and luckily all was ok.

  • grayracer513

Posted March 10, 2015 - 07:14 AM


This bike is ridden on dunes a lot which will make a bike run hotter and leaner too. Might have cooked the piston.


It can make them run hotter just because of the drag imposed by sand and the extra throttle needed to compensate, but it will not make them run leaner.

  • moto867

Posted March 10, 2015 - 12:25 PM


Sounds kinda like a cracked piston. I can't see the rings wearing that much in 30 hours unless he sucked lots of sand. But then the valves would be leaking to

  • grayracer513

Posted March 10, 2015 - 02:46 PM


Overheating far enough just once will take all the spring out of the rings, and damage the exhaust valves.  I fixed one where the head had gotten hot enough between the exhaust valve seats to reach the melt point, and the seats were out of round to the point where we almost couldn't save them.

  • boegey

Posted March 10, 2015 - 05:14 PM


Yer it seems to be running fine as normal Yer I got back and put more fluid in straight away it was only about 30 mm below the lip

  • deckdog66

Posted April 14, 2015 - 08:06 AM


Getting back to the original topic; the rings turned out to be warped and the lands damaged. Also, the rings were not clocked correctly. In addition, the piston and cylinder were moderately scored on the exhaust side. I rebuilt using a big bore kit. Awesome power restored.

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