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Dirt bike blew up :/

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Hello everyone I was riding my 1998 Cr250r and it started to get really boggy and made a knocking noise and shut off, and the kick start will not go down. So I am wandering if this could be possibly the top end or could it be the bottom end too? Also I almost got the bike top end apart tonight but got tired and called it a night. I am needing your thoughts on about boring it out. So I am wanting to bore the bike out to a Cr280r and have the head port an polished and have a shave head. Do you all think the bike will be reliable or should I just but back a factory piston in the bike? Any info will be great.

Thanks for all replies:ride:

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Got the top end off looks like the piston skirt shatterd. I am wandering though, could this possibly go to my bottom end and causing it not to turn over? Here are some pics that I took.

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yikes. thats what happens when you let a piston go too long without a rebuild. from the looks of it, that piston was in there a LONG time. time for a new crank and piston and what ever else got FUBARed in the process.

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Dude, that's one ugly cylinder...

I can't tell from the pictures if your cylinder is gouged or not. If it's not, I would not recommend going big bore on that year engine. You might need to get someone with some experience to check it out. Check it out with a micrometer to see if the bore is still round while your at it.

Obviously you should split your cases and clean that mess out. You very well could have messed up the crank bearings, but it's all going to have to come apart to check it out and do the job right--whether that consists of cleaning and rinsing, or replacing the crank bears and/or crankshaft assembly.

You'll probably want to replace the head, but it looks to me like you can still use it if money is an issue. The pitting on a head can lead to hot spots that cause detonation under the right circumstances, but I've run them before without problem.

I hope it all checks out OK for you!

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Lesson learned. That motor looks like it's been negleted from maintnace. From the looks of the piston it has a lot of hr's & could possibly be the original piston. I would definatley check the bottom end out & look for dedri. Can you turn the crank assembly by hand now that the topend is apart ? A piece of the skirt could have wedged it self in there. If it was me I'd do a complete rebuild top & bottom as it looks like it has a lot of hrs...

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Ouch, yeah you are going to have to split the cases for sure. I'd imagine some debris go into the crank bearings and hurt them along with your cylinder/piston mess. BTW, you need to clean your PV. lol

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Lesson learned. That motor looks like it's been negleted from maintnace. From the looks of the piston it has a lot of hr's & could possibly be the original piston. I would definatley check the bottom end out & look for dedri. Can you turn the crank assembly by hand now that the topend is apart ? A piece of the skirt could have wedged it self in there. If it was me I'd do a complete rebuild top & bottom as it looks like it has a lot of hrs...

+1......top and bottom end rebuild.

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.. most often the cases get cracked from this .. you need a full rebuild of that engine or its going to be a time bomb with a very SHORT fuse

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Hello everyone I was riding my 1998 Cr250r and it started to get really boggy and made a knocking noise and shut off, and the kick start will not go down. So I am wandering if this could be possibly the top end or could it be the bottom end too? Also I almost got the bike top end apart tonight but got tired and called it a night. I am needing your thoughts on about boring it out. So I am wanting to bore the bike out to a Cr280r and have the head port an polished and have a shave head. Do you all think the bike will be reliable or should I just but back a factory piston in the bike? Any info will be great.

Thanks for all replies:ride:

Looks horrible dude,always clean ur air filter every ride, its time for a top and bottom end rebuild,check out ebay by the user name Boss bearings have a full bottom end bearing and seal kit for $139.99 including shipping ,get wossner piston kit,hot rods rod kit fitted to cranck and balance ,get ur jug rebuilt back to std specification,some one that knows what they are doing to rebuild bottom end,want cheapest cost for labour,lots of dreamers out there will pull fugures out the he$ds and just rip you off, phone around or purchase a manual and tools do it your self (cheaper).

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similar thing happned to me, $1800 later and its basically a new engine, in that price i got the linkage bearing kit and wheel bearings

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