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Motor blew up, top end rebuild!

23K views 45 replies 10 participants last post by  autonoob 
#1 ·
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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#3 · (Edited)
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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#4 ·
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.
 
#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.
 
#10 ·
****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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#14 · (Edited)
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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#15 ·
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.
 
#16 ·
Should be a link for the service manual here, in pdf. If you can't find it let me know.

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#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.
 
#21 ·
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.

This will be hard to achieve, as one will cancel out the other. :eek:hno: I'd personally stay away from the 13t front sprocket. I have a 14 one my original and a 15 on the other. With the added mods they both pull really well down low.
 
#20 ·
so are your only 2 post :|
 
#26 · (Edited)
I did grind on the case saver, for extra clearance. It did go on without grinding, but was really close to touching, so I opened it up a quarter inch or so. I'm not sure if it was necessary or not, but I sure felt better about doing it, than I would of had I not.

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#27 ·
Glad to see a fresh thread and im not the only guy with one left. Ive been having upper end issues and the guy at Duncan basically told go for the gusto or dont bother and stay stock I loved this thing for the 10yrs ive owned it but this builder has really just worn me out with problems. Most scary thing about the lower or anything cool is they never post again after they start the build so you never know if it worked out or wasted money. Good luck and let us know how it goes
 
#28 ·
I know, I tried to do what I like in posts but don't see very much. Be very specific with my problems, post too many pictures, and explain the end goal so if anyone with similar problems or ideas then they can learn a little bit from my experience before they start on theirs. I am waiting until at least tomorrow to buy any parts to kind of finalize my research and see if a big bore kit is worth the extra money. I probably will end up getting it, just want to be sure before a big purchase happens. But i'll be sure to keep everyone posted!
 
#29 ·
*** UPDATE ***

Finally back out there and got the valves out and to what M_Quick was probably trying to get me to check, 3 of the 4 valve guides were cracked and 2 of my valves were barely bent. I'm not sure how bent they need to be to be unusable but i'm sure that any bend will cause problems. So I'll probably need to be looking at getting all new valves and new guides? I'm not sure what's it's called but the section of the motor where the valves are located. I tried my best to show the valves and guides in the pictures attached to this. As far as cracking the motor open, it has came to be impossible for me to do it by myself with given I don't have air tools yet to help me. I seemed to get everything I need to off except the nut holding the clutch on? It's behind the 6 spring loaded bolts and spins whenever the motor doesn't. I've tried putting it into gear and I don't know. I'm sure i'll figure something else out or one or the people reading this will have a better idea than me, but as of right now, the motor is still together and I have no idea how to get it apart. I just look for something that may be holding it and try to take it off. Doesn't seem to be working so far sadly.. Haha Any ideas would be very very much appreciated!
 

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#30 ·
That part with the valves is called the cylinder head, I suggest you take it to a shop to get the new valves installed. It's kinda hard to do on your own. And as for that part spinning is because you need to get a tool called the clutch holder to keep it from spinning as you unbolt it. Do a quick Google search for trx700 clutch holder and you'll see what you need.
 
#31 ·
Okay, I plan to take the cylinder head to Southern Honda Powersports whenever I go back to my hometown so they could see what one will cost and see about the valves and stuff, as for the part, I ordered it and it should be here tomorrow. Once I get that, I shall attempt to split the motor yet again and hopefully have more luck!
 
#32 ·
Finally got the motor split using that clutch holder. Thank you Kubi! figured out that i'm really glad i split the motor because during the slow process of splitting them apart, sooooo much metal came out of where all of the gears are and lodged into places that i'd never get out had i not split the motor. My garage is the messiest it will probably ever be with everything thrown around and parts everywhere. Looking at everything on the floor, it's so intimidating thinking about putting it back together. I hope that when i get to certain parts, my memory will spark but first i have to buy parts and get them, then clean the motor. Once it's clean, I'll begin piecing it back together one baby step at a time. Until then enjoy these pictures which include my disaster of a garage and the trash that came from inside my motor.
 

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#33 ·
Good gawd, that last picture is haunting! I'm glad you got it apart, good luck with the reassemble.

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#34 ·
Yeah it will be tough, but i should be able to get it done. I just can't get past the whole buying a whole $460 cylinder case just for those little cracks and spending 140 on valves because they are just barely bent. Aside from that, I could have it up and running very soon. Haha
 
#35 ·
Well you will for sure want to replace those valves. The cylinder head is probably okay, you just need to replace the valve guides. Now from what I remember your cylinder it's self needs replaced but, it's alot cheaper than the head!

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#36 ·
Okay so I apologize for not replying or anything of that sort. Classes started back and i took a minor needed vacation to the beach with some family. But I haven't made any progress, I have attempted to remove the valve guides but have been quite unsuccessful using methods i've found on the web via youtube. I don't feel comfortable enough using brute force because if I screw up and break something, i'm out 450 more dollars. I'm basically to the point of taking it to some sort of shop and seeing if they can remove the guides, put mine in, and give it back to me. But i'm not sure the kind of shop to do that. I've never had to put anything in a shop because i've been able to do it myself but this one has stumped me. If anyone has any ideas of how i may be able to remove them or just reference me to the type of shop i need to be looking for, (machine shop, motor repair, four wheeler shop, honda), I would greatly appreciate any guidance at this point!
 
#37 ·
IDK what method you tried from youtube. Did you try heating it up in the oven? I'm pretty sure the manual will tell you the proper temp. And while waiting for it to heat up, place new guides in the freezer. As far as shops go, Idk your area, but any machine shop should be able to do this. If you want it port and polished then, I'd look at a shop like EHS racing or similar.
 
#38 ·
First I tried drilling them out and it may have done more damage than good. So then I tried using the old valve and a socket and a rubber mallet and couldn't get them to move. The oven is currently heating up with new guides in the freezer. I'm assuming I try putting the valve with a rubber mallet and see if that will work with the heat. Another thing i noticed was the new valves didn't slide into the new guides. I'm assuming the guides need to be heated with the valves cooled but not sure. I hope that's the case anyways.. Haha I bought all of the parts at the same time on partzilla so they should be right but idk.
 
#41 ·
**Update**

Still no progress. I guess i've just been dreading the rebuild process and letting this part stop me. I'm not sure if i should even bother with taking it to the machine shop at this point or if i should just buy a new one. I haven't taken it to the shop to get any quotes or know of the general cost to get something like this done but I know that i've done more bad than good with trying to get the valve guides out. The positive to buying new is obviously everything would be new short of the crank and cam in the engine. Downside would be the 450 dollar price tag. But if i'm going to have to spend 200 on a machine shop for a used part that seems to be very worn, I'd pay the extra to have new. Even though i'd still have to go to the machine shop to have the guides pressed into the new cylinder head. I don't know the best route, i'm definitely on the fences about it and this is the last piece of the puzzle before the long journey of putting this SOB back together.
 

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#43 ·
It's the design of the "slipper" piston.

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#44 · (Edited)
Is that a defect with the stock 700xx piston or aftermarket pistons? I thought that Honda would know better, given their 70 years of designing motorcycle engines. A well designed slipper piston should function just as good as a full skirt design.

All I can find is this thread on here.
https://www.club700xx.com/vb/8-moto.../946-larger-capacity-oil-tank-2.html#post9131


Is there any more info on this issue? Any suggestions to mitigate it? The only thing I can think of is poor piston lubrication causing excess wear on the wrist pin or cylinder wall (and then side skirts/rings/ring lands).

Solution is to run high quality oil and change it often?
 
#45 ·
hey when you brake things you go all out
 
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