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07 kx250f stuck crankshaft

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I recently had a post up about my kx250f locking up while i was riding a track. I was told it was the tranny cause whe i opened the top end nothing seemed to be damaged, and the crank seemed fine just by looking at it. When i split the casing the tranny was fine. but i found broken metal on the flywheel/magneto. im guessing that was just from normal wear and tear? Im not sure about that, but the main problem i see is when i spin my crank, it gets stuck after like 4 or 5 rotations, and then locks up. Does this mean i need a new bottome end? and if so what tools would i need to remove it? Hope you guys can help me out.

Thanks

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go ahead and replace the crank... you can get a wiseco bottom end kit with crank, rod, gaskets, and bearings for $200 on ebay. all you need to get the old one out is a small sledge hammer

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Thanks, now is there any special way im supposed to hit it with the hammer?

and when I put in the new crank and bearings is there a special way to do that?

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Thanks, now is there any special way im supposed to hit it with the hammer?

and when I put in the new crank and bearings is there a special way to do that?

NO! don't hit it with a hammer!!!!!!!!!

use the case splitter you bought to push the crank out of the other side of the case.. Just remember you need to take of the primary drive of the crank first. It's reverse thread..

you can also use the splitter to press the bearings out of the case also. [most likley the right side bearing will press out of the case with the crank but the left side or ignition side is most likly still in the case.. just hook the case splitter back up and find a deep well socket big enough that you can use to with the case splitter to press the bearing out..

During installation heat the bearing seat up on the case where water will boil off in less then a second You need to find some dry ice before this.. freeze the bearing for at least 10 minutes before you start the heat on the case.. when the case it heated remove the bearing from the dry ice wipe it down with wd40 [this removes any condensation and lubricates the bearing] then just drop the bearing into the slot.. Due to the contraction of it being cold and the expansion of the case from the heat it will literly just drop into the slots.

do this for the other side remember you can't install the oil seal on the right side still after you install the crank.

Next. you need to let it set for a while let it get to room temp before you move on..

crank installation is just about the same way.. if you're going to cool the crank down just besure that you leave it in the oil filled bag before doin so. You also don't need to do it as long. as the main bearings..

heat up the right side crank bearing inner race. Do not torch this long it doesn't need to be anywhere near as hot as the case. take the crank and remove it from the bag and it should just slide right into the main bearing..

now hurry up and apply your liquid gasket. Then heat the other main bearing and drop it on to the crank. The cases wont just slip right back together. you're gonna need to get the output shaft alligned and tap it a little with a rubber mallet and it should then just fall right into place. Now torque all case bolts and bammo you're done.

Side note! with the main bearings being heated. Once the case is put togther untill they cool down do not try and spin the crank. It wont happen due to the expansion you may hurt the bearing at this time.. Once I get the cases back togther I normaly spray wd40 or put oil into the main bearings to cool down and replenish any disapated lube that was in them.

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NO! don't hit it with a hammer!!!!!!!!!

use the case splitter you bought to push the crank out of the other side of the case.. Just remember you need to take of the primary drive of the crank first. It's reverse thread..

you can also use the splitter to press the bearings out of the case also. [most likley the right side bearing will press out of the case with the crank but the left side or ignition side is most likly still in the case.. just hook the case splitter back up and find a deep well socket big enough that you can use to with the case splitter to press the bearing out..

During installation heat the bearing seat up on the case where water will boil off in less then a second You need to find some dry ice before this.. freeze the bearing for at least 10 minutes before you start the heat on the case.. when the case it heated remove the bearing from the dry ice wipe it down with wd40 [this removes any condensation and lubricates the bearing] then just drop the bearing into the slot.. Due to the contraction of it being cold and the expansion of the case from the heat it will literly just drop into the slots.

do this for the other side remember you can't install the oil seal on the right side still after you install the crank.

Next. you need to let it set for a while let it get to room temp before you move on..

crank installation is just about the same way.. if you're going to cool the crank down just besure that you leave it in the oil filled bag before doin so. You also don't need to do it as long. as the main bearings..

heat up the right side crank bearing inner race. Do not torch this long it doesn't need to be anywhere near as hot as the case. take the crank and remove it from the bag and it should just slide right into the main bearing..

now hurry up and apply your liquid gasket. Then heat the other main bearing and drop it on to the crank. The cases wont just slip right back together. you're gonna need to get the output shaft alligned and tap it a little with a rubber mallet and it should then just fall right into place. Now torque all case bolts and bammo you're done.

Side note! with the main bearings being heated. Once the case is put togther untill they cool down do not try and spin the crank. It wont happen due to the expansion you may hurt the bearing at this time.. Once I get the cases back togther I normaly spray wd40 or put oil into the main bearings to cool down and replenish any disapated lube that was in them.

if your going to replace the crankshaft anyway what is it going to hurt to knock it out? i have always done that and it never affected anything as long as your careful

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some people dont have those fancy tools like a case splitter, or a torch. i have never used either of the two and all the bottom ends i have rebuilt are still working fine

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Well ktmforlife you can do your rebuilds your way.. pounding the crank out with a hammer will destroy the crank.. His crank maybe just fine and the it may just be the crank bearings that went south.

Second if you are splitting cases with just screwdrivers you're going to break a case eventualy! a tusk case splitter is 50 dollars money worth spent! some tools are life long once you buy them. If you split cases once a year the tool is worth the money!

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Well ktmforlife you can do your rebuilds your way.. pounding the crank out with a hammer will destroy the crank.. His crank maybe just fine and the it may just be the crank bearings that went south.

Second if you are splitting cases with just screwdrivers you're going to break a case eventualy! a tusk case splitter is 50 dollars money worth spent! some tools are life long once you buy them. If you split cases once a year the tool is worth the money!

ahh you make a good point. i have always just replaced the crank even if it just needed a rod bearing. i dont use a screwdriver to split the cases i use a small rubber mallet (which is what the honda and yamaha service manuals told me to do.... the zook manual is the only one that said get a splitter but the mallet worked fine on it too.)

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ahh you make a good point. i have always just replaced the crank even if it just needed a rod bearing. i dont use a screwdriver to split the cases i use a small rubber mallet (which is what the honda and yamaha service manuals told me to do.... the zook manual is the only one that said get a splitter but the mallet worked fine on it too.)

if it needs a rod bearing I would put a whole new crank in.. how ever if it was just the main bearings the ones that the crank asembly ride on in the case then I would replace those and re-use the crank. How ever if the current crank has anymore then say 50hrs I would just replace the crank.

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if it needs a rod bearing I would put a whole new crank in.. how ever if it was just the main bearings the ones that the crank asembly ride on in the case then I would replace those and re-use the crank. How ever if the current crank has anymore then say 50hrs I would just replace the crank.

:smirk:

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if it needs a rod bearing I would put a whole new crank in.. how ever if it was just the main bearings the ones that the crank asembly ride on in the case then I would replace those and re-use the crank. How ever if the current crank has anymore then say 50hrs I would just replace the crank.

the small end on the rod will wear out way before the rest of the crank anyway so when the small end is out of spec. just replace it with a new complete crank and bearings

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Im pretty. Sure its the rod bearing or something oother than the main bearings, because it almost seems like the rod gets stuck when spinning due to something in the middle of the crank

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well, then press the crank out. Spin the rod with the crank half stationary if it seizes then its the big end bearing. if it doesn't seize it's the main bearings.. Either way you're gonna replace the main bearings.. If you have more then 25hrs on the crank just replace it..

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