Well, I got the diagnosis back from my dealer. Basically, looks like the bad piece was the piston. The connecting rod ripped right out of the bottom of the piston, punched the cylinder wall, and that twisted the rod. The piston flew up, and punched a valve through the head. There was chrapnel everywhere, casings are busted up inside, there are shavings all through the oil system and in the oil pump. Basically it was a catastrophic once it was all said and done. Sounds like I might end up getting a new complete engine because this one is so badly damaged, all under warranty. I don't know why the rod ripped out of the piston. There was no cylinder scoring to indicate any lack in fuel or lubrication problems. It looks as if it just happened to be a faulty piston and the rod ripped out. For those wondering, my engine was completely stock, no cam mod or 13:1 piston. So I really don't know why it blew out, and I haven't heard of anybody else having that problem unless they went to the higher comp piston. Hopefully this new engine works fine...can't be blowing another one during a race!!!

 

I was going to say it sounds like the whole engine is toast. I hope they do replace the whole thing. I wouldn't want that one repaired.

 

Sounds Identical to Selectors explosion only he had the 13:1 piston and other mods. Wonder who makes the pistons used in the YFZ?

 

There's been a couple of post on another forum, which talks about a couple of YFZ's that the rods broke too. Hopefully these are a rare problem. Both were stock.

This is the post.

Now don't get me wrong, I love those YFZ's, very quick. But don't be suprised if you start seeing them drop like flies around you. Riding with my buddy yesterday who has one. He had it topped out in fifth trying to see how fast he could get his TrailTech to register and the motor blew up!!!! Three holes in the bottom of the case and three holes in the cylinder. Oil and smoke spewing EVERYWHERE. Took the motor out and brought it by the dealership who aleady had another YFZ there with the same problem just not as severe. What there saying it looks like is the rod breaking in half, they're waiting to see what yamaha says..... I know our preddy's may have some kinks but not like this!!!

 

wow, thats ruff...
will they have a new engine by your first race...?
gonna suck breaking it in too... hopefully you will have time to if you do get it back before your race.

 

sounds kinda like mine in the last ice race
my rod bearing went along with the piston and other stuff....and mine still has the stock pipe with the baffle removed.

 

Hmm, makes me wonder if the rod berring was the cause of mine too? Dealer wasn't that specific, just said the rod ripped out the bottom of the piston. Just hope the new one doesn't do it! If everything goes as scheduled, I should get the new engine and the quad back 1 week before the 1st race....and I still have some stuff to bolt on the quad, skids, and small stuff, and billet head plug. Might have to put in some late nights to have it ready to go...and need lots of seat time in that week! I wonder if this is going to be a problem...cause I will be really unhappy if it happens again and shells another engine!

 

Well that is rotten isnt it?? Hopefully you can get it back together before the first race!

 

Hey man still wondering where you are racing at? be pretty kewl to meet up with ya sometime.

 

Yaaaa, visit this web page here for the race schedules in Iowa, and that is where you will find me! First race is the 25th of april in indianola!