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Bike Blew Up in 14.7 Hours --- Pics Included

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I was racing this weekend and blew up my YZ250 in the 2nd moto. I only had 14.7 hours on the top end (I usually replace every 20-25 hours). Right before the face of a jump the bike made a bang and immediately bogged out. I gently pushed down once on the kickstarter with my hand and realized I had no compression. I disassembled the bike tonight to find a decent amount of damage (as shown below).

The cylinder obviously needs to be replated and I'll need a new head. It looks like a ring possibly snagged the exhaust port or hit the power valve. Is it possible for it to hit the power valve? Does the power valve ever need to be adjusted?

The crank is still good. Initially I was planning on splitting the cases to remove any pieces of metal from the bottom end because I cannot account for all of the pieces since it pretty much shattered; but, a friend had suggested to remove the engine and turn it upside down and spray solvent or some type of cleaner in the bottom end to wash it out, rather than split the cases. I don't know if this is a good idea or not. I'm not anticipating that there would be much metal in the bottom of the crank case. What would you do?

2011-09-20_21-33-46_586.jpg

2011-09-20_21-33-56_295.jpg

2011-09-20_21-34-15_730.jpg

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Wow, that sucks!

Yes, you need to split the cases. A freind of mine just did the same thing to his CR250 a few weeks ago. He turned the motor upside down and cleaned the crank case with diesel and some other kinds of solvents trying to get all the aluminum. He said he cleaned it very thoroughly, but he just had to split the case today and found tons more. I wouldn't want to put a fresh top-end in only to have aluminum sucked into the cylinder and chew up the plating and piston.

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Looks like you need a new powervalve also, or grind yours down for clearance. They wear out on the stops on the outside of the cylinder and hit the rings. I think that's what happened here.

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Looks like you need a new powervalve also, or grind yours down for clearance. They wear out on the stops on the outside of the cylinder and hit the rings. I think that's what happened here.

How would I go about grinding down the power valve, as I imagine maintaining the shape and angle is crucial? And where are the stops you are referring to?

Please keep the suggestions coming...

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Man that sucks. But look at the bright side, now you have an excuse to send it to Eric and get a 295 kit. It will cost you the same or more to repair all of that to a 250, might as well go big.

Yea, as others have said definitely split the cases.

MAX!!!

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:bonk:The PV's may have been put in backwards.:smashpc:

The power valve has never been removed since new. Are you implying that it may have been installed backwards from the factory?

Man that sucks. But look at the bright side, now you have an excuse to send it to Eric and get a 295 kit. It will cost you the same or more to repair all of that to a 250, might as well go big.

Yea, as others have said definitely split the cases.

MAX!!!

Yes, it's very tempting to go with the 295 kit. I like the flexibility of being able to race either the 250 or Open class so that's why I would like to keep it as a 250. And I'm not sure how the 295 would be for MX---I would be afraid I would lose the over-rev that I have as a 250, but the torque gain from the 295 would probably compensate.

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The power valve has never been removed since new. Are you implying that it may have been installed backwards from the factory?

Yes, it's very tempting to go with the 295 kit. I like the flexibility of being able to race either the 250 or Open class so that's why I would like to keep it as a 250. And I'm not sure how the 295 would be for MX---I would be afraid I would lose the over-rev that I have as a 250, but the torque gain from the 295 would probably compensate.

The 295 is sick and it is great on the track. I had Eric build mine for higher compression(race gas set up) and for more mid to high end performance. Going from a 250 to a 295 you are gaining 18% overall so I didn't feel like I needed Eric to build me a low to mid motor. My bike's over rev is pretty impressive, especially 2nd gear, it just keeps pulling, all the gears pull longer. Since you have to rebuild the top end and repair your cylinder I strongly suggest paying Eric the $600 for the 295 :smashpc:

MAX!!!

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I was racing this weekend and blew up my YZ250 in the 2nd moto. I only had 14.7 hours on the top end (I usually replace every 20-25 hours). Right before the face of a jump the bike made a bang and immediately bogged out. I gently pushed down once on the kickstarter with my hand and realized I had no compression. I disassembled the bike tonight to find a decent amount of damage (as shown below).

The cylinder obviously needs to be replated and I'll need a new head. It looks like a ring possibly snagged the exhaust port or hit the power valve. Is it possible for it to hit the power valve? Does the power valve ever need to be adjusted?

The crank is still good. Initially I was planning on splitting the cases to remove any pieces of metal from the bottom end because I cannot account for all of the pieces since it pretty much shattered; but, a friend had suggested to remove the engine and turn it upside down and spray solvent or some type of cleaner in the bottom end to wash it out, rather than split the cases. I don't know if this is a good idea or not. I'm not anticipating that there would be much metal in the bottom of the crank case. What would you do?

2011-09-20_21-33-46_586.jpg

2011-09-20_21-33-56_295.jpg

2011-09-20_21-34-15_730.jpg

Damn thats about what mine looked like at 40 hours when it let go. I would suggest splitting the cases. Also, it looks like the bike was having a predetonation issue which could lead to the piston getting a bit cockeyed and clipping the exhaust port. Thats what I think happened but I may be wrong.

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Man, that sucks. Perhaps something got in there... it's a long shot, but check your reed cage screws and stuff like that. Could be that the ring just fatigued and broke, or detonation broke the piston crown.

I would split those cases for piece of mind. It will give you something to do while you wait for that re-plate or big bore.

Powervalve is in the right way in your pic. I have a spare cylinder sitting here on my desk, PV orientation is exactly the same.

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bummer, on a good note, 600 bucks and your back on the track. If it was a 4 stroke, you would have to sell your left arm

And nut and leg, don't forget the leg.

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Wow, that sucks!

Yes, you need to split the cases. A freind of mine just did the same thing to his CR250 a few weeks ago. He turned the motor upside down and cleaned the crank case with diesel and some other kinds of solvents trying to get all the aluminum. He said he cleaned it very thoroughly, but he just had to split the case today and found tons more. I wouldn't want to put a fresh top-end in only to have aluminum sucked into the cylinder and chew up the plating and piston.

Been there, done that. Don't risk it, split cases and do it right.

...

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How would I go about grinding down the power valve, as I imagine maintaining the shape and angle is crucial? And where are the stops you are referring to?

Please keep the suggestions coming...

I'm not sure how crucial the grinding is,I've done a 125 not a 250. I just ground down the part showing inside the cylinder. It's all in the manual. You shouldn't be able to see any of the valve looking down the cylinder wall.

The "stops" are on the other side, they stop it from closing too far but can wear with vibration(they are just the sides of the valve). Acces is behind the rectangle cover in the front.

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The feedback has been great so far.

The PV looks not touched to me, most likely the ring broke. How old is the bike? And the cylinder is still OEM?

Upon further inspection, it does not look like the power valve incurred much damage. There are two small dents in it, so I will likely replace it anyhow, but its hard to tell if the ring snagged the port or the power valve. I checked and it does not look like the power valve extends at all into the cylinder so I think it's safe to assume a ring got snagged on the exhaust port maybe from excessive clearance causing rocking?.

The bike is a 2006 YZ250 and the cylinder is OEM. I know you may think a 2006 has plenty of hours on it but I literally bought it off a 50+ year old guy who still had the stock tires and chain on it. Since I bought it I have put a total of 17.1 hours on it. I replaced the piston at 2.4 hours and the cylinder looked great.

Damn thats about what mine looked like at 40 hours when it let go. I would suggest splitting the cases. Also, it looks like the bike was having a predetonation issue which could lead to the piston getting a bit cockeyed and clipping the exhaust port. Thats what I think happened but I may be wrong.

My jetting is pretty close to spot on, and if anything is a little on the rich side. I had run 93 pump gas at first but decided to run a 50/50 mix of 112 race fuel with 93 pump. I didn't notice pinging in either situations so to save some money I switched back to straight 93 pump gas. In both cases I mix oil at 32:1.

Man, that sucks. Perhaps something got in there... it's a long shot, but check your reed cage screws and stuff like that. Could be that the ring just fatigued and broke, or detonation broke the piston crown.

I have the V-Force reed cage which does not have screws, so I'm confident no foreign objects entered the cylinder. All of these comments of possible detonation causing the damage has got me considering making the switch back to race gas for safe measures once it gets rebuilt.

Any info on what year heads will fit my 2006 YZ250? I don't want a 2011 or 2012 because I believe they are the Euro spec heads which have a bit less compression due to increased bowl volume. What is the range of years that would work? 2002-2010?

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