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Okay so about 3 years ago, (i know a long time ago), I was riding my 700xx at a cruising speed of around 45-50 in 5th gear when it just locked up. My instinct was to pull in the clutch immediately and roll to a stop. I look down and notice a crap ton of coolant pouring out of a rather large hole right next to my exhaust. I immediately call and get it home and it has sat like that until yesterday when i began tearing into it. I got all the way to having the valve cover? or whatever it is called off and the plate that i'd assume being the transmission cover. I am fairly good with engines and know how they operate and stuff, just don't know terms of most stuff. I have attached pictures that I have taken in hopes that someone with a lot more experience than me can help me. I am just looking to get the motor apart and replace anything that is busted with not stock parts, just not anything crazy that I will have to buy a programmer and dyno it and stuff. I rode this thing every day and loved every minute of it. Tore me apart when it tore up and have wanted to fix it since it broke. So any help is very much appreciated, and any part recommendations/websites to get those parts would be much appreciated as well! I want to put new parts back in it, but I'm a college student so money isn't a thing I have a lot of.
 

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Discussion Starter #2
I really have no idea why the pictures rotated themselves.. I guess it automatically did it because of the resolution difference. I apologize for that in advance!
 

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Sounds like your piston came apart like mine. Hopefully your crank is okay. But you need to open up from the top, not the sides. Take valve cover off, then the jug. Inspect valves, rods, cam chain. Your piston will most likely be mangled.

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Sounds like your piston came apart like mine. Hopefully your crank is okay. But you need to open up from the top, not the sides. Take valve cover off, then the jug. Inspect valves, rods, cam chain. Your piston will most likely be mangled.

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I am curious as to why one of these engines would fail? I have read several threads where guys have mentioned that their 700xx had blown the engine. Its got me a little nervous. I like to push the happy lever as much as possible.
 

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I am curious as to why one of these engines would fail? I have read several threads where guys have mentioned that their 700xx had blown the engine. Its got me a little nervous. I like to push the happy lever as much as possible.
Mine was the design of the piston. If you look at the piston, it has skirts on 2 sides. Once one side cracks, there's nothing left to hold it in place. So it slaps around and cracks the jug/cylinder.

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Discussion Starter #6
I tried that at the beginning but seems as if the cam chain is holding it down and I don't see a way i can just slide the cam out of it and lift it out. I removed the 4 top bolts on the inside of the valve cover and got one side to pry up a little, but the cam chain side didn't seem to budge at all, leading me to believe the chain had to be removed. So i tried following the chain down to the side plate and seen the many pieces of aluminum or whatever it is all down in the bottom so i'll clean it out. I was wondering if there was some special way to remove the valve portion of the motor to get to the jug? Or if the cam/cam chain has to be removed. And if they have to be removed, how to go about it. I tried putting a nut and breaker bar on the little sprocket and the motor just spun, even when it was in gear. So instead of doing more damage, i figured i'd quit and research more before I carried on with the journey.
 

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Discussion Starter #7
I am curious as to why one of these engines would fail? I have read several threads where guys have mentioned that their 700xx had blown the engine. Its got me a little nervous. I like to push the happy lever as much as possible.
I'm not really sure. It seems to be the luck of the draw to me, which sucks.. But I guess there was a reason they only made these things for 2 years? I'm not really sure. I hope you have better luck than us though! :lmao:
 

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You're gonna have to break the chain to be able to do anything, most likely it's the Piston as M_Quick mentioned.
 

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You're gonna have to break the chain to be able to do anything, most likely it's the Piston as M_Quick mentioned.
Surely there is a way other than breaking it to get it off.. Probably similar to the way you put it on, but with reverse steps? I don't know, that just seems kinda weird that the only way to get it off is to break it.
 

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****UPDATE****

I finally got off the cam chain and got the rest of the motor apart, it seems as if m_quick was correct. The cylinder got a crack in it and blew out causing extensive damage to the piston and cylinder. The valves seems to be in okay condition? but I'm not sure if the gap that I tried my best to show is suppose to be there or not; they definitely look used and I will probably be getting new ones since I already have it apart. As far as the crank goes, I'm not to sure on what a bad one would look like? And I don't want to take the motor all the way out of the frame just to check, unless I have to.. Obviously I want to do everything I can to where when I put it back together, I have a quality reliable quad, rather than a ticking time bomb because I halfway did it. Is there any kind of like test or anything that would tell me if the crank was bad? The motor spins great and the piston still goes in its usual motion. The piston arm? is still in good shape it seems. Idk, i have attached some decent photos of the damage done and some things that maybe I thought may need replaced but might not? As I said before, any and all help is much appreciated.
 

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Discussion Starter #11
****UPDATE****

I finally got off the cam chain and got the rest of the motor apart, it seems as if m_quick was correct. The cylinder got a crack in it and blew out causing extensive damage to the piston and cylinder. The valves seems to be in okay condition? but I'm not sure if the gap that I tried my best to show is suppose to be there or not; they definitely look used and I will probably be getting new ones since I already have it apart. As far as the crank goes, I'm not to sure on what a bad one would look like? And I don't want to take the motor all the way out of the frame just to check, unless I have to.. Obviously I want to do everything I can to where when I put it back together, I have a quality reliable quad, rather than a ticking time bomb because I halfway did it. Is there any kind of like test or anything that would tell me if the crank was bad? The motor spins great and the piston still goes in its usual motion. The piston arm? is still in good shape it seems. Idk, i have attached some decent photos of the damage done and some things that maybe I thought may need replaced but might not? As I said before, any and all help is much appreciated.
More pictures
 

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Mine was the design of the piston. If you look at the piston, it has skirts on 2 sides. Once one side cracks, there's nothing left to hold it in place. So it slaps around and cracks the jug/cylinder.

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So these are stock pistons that are failing and causing the engine to explode?
 

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So these are stock pistons that are failing and causing the engine to explode?
It's just a issue with any slipper piston, imo. And that's what cracked here causing the jug to crack, not the other way around.

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To OP most people will tell you to replace the crank and bearings. And to do this you will need to pull motor and split the case. If your wrist pin comes out easy, that's a good sign crank may be okay. If you don't wanna replace the crank, you will have to make every effort to clean all the shrapnel out of the bottom of motor. Most of the time when this happens the motor will lock before damaging the crank. I'm wondering since you had the issue with the cam chain if you have the service manual? Also replace the cam chain while apart. And you need to pull your valve springs to check the rods and valve guides in the head. When mine blew all the valve rods were bent and atleast one valve guide cracked.

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To OP most people will tell you to replace the crank and bearings. And to do this you will need to pull motor and split the case. If your wrist pin comes out easy, that's a good sign crank may be okay. If you don't wanna replace the crank, you will have to make every effort to clean all the shrapnel out of the bottom of motor. Most of the time when this happens the motor will lock before damaging the crank. I'm wondering since you had the issue with the cam chain if you have the service manual? Also replace the cam chain while apart. And you need to pull your valve springs to check the rods and valve guides in the head. When mine blew the all rods were bent and atleast one valve guide cracked.

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I do have the service manual somewhere in my garage, I'm not sure where but I should have found it and researched it rather than googling everything.. Minor setback but I will be sure to do so in the future. The only reason i wouldn't want to replace the crank is the price tag that is on them. But i guess replacing it now would save money in the future so I guess i will go the extra mile into taking everything apart. I'd rather do that anyway just to triple check all of the shrapnel is out. Part of me wants to do whats needed and slap it back together but the other half wants to take my time to do everything correctly to ensure the life of the quad. I just wasn't sure at first if it was 100% necessary to take everything apart since it was just the top end. I guess i'll spend tomorrow ripping it from the cage! I'm sure more pictures will come.
 

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Should be a link for the service manual here, in pdf. If you can't find it let me know.

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Discussion Starter #17
Got the motor out. Have gotten all the bolts that I could find to split it and couldn't get it to come apart. Not sure if you have to take the main gears off of the main axle in there but I will try to do that when I have my girlfriend there to help. Everything still seems to be in good shape though other than the obviously destroyed stuff. May go ahead and start ordering a couple parts that I know for sure i will need. Any recommendations for anything? I was thinking of the big bore kit but don't know if it's plug and play or I'd have to get the cylinder or whatever machined to make it work. I already know i'm going to get 2 new sprockets both the front and the back ones to increase overall speed, but still try to keep my power down low. That, and i know i will need new tires and wheels shortly after fixing it due to it sitting for so long.
 

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From what I know, the big bore kit is plug and play. And if you decide to replace your crank, you can replace it with a stroker crank.
 

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