bent or twisted crankshaft

[dave916]

bought a secondhand engine , turns out the crankshaft it bent or twisted  ,when i rotate the engine the flywheel and clutch ends are both move up and down 2-3mm,the webs are also moving 1-2mm toward casing , so bad i think it worn the inside of flywheel and the cases are cracking where they bolt together
how common is this??

[PowerFiend]

Sounds like someone did not properly rebuild the crank. This is not a factory screwup.

[cbxracer30]

This is not a common thing, sounds to me like someone had a major piston failure , fixed the piston problem but failed to check the crank. The damage probably happened the first time the motor was refired. Cases can be welded , and the crank should be fixable as for the flywheel , it should be ok but it probably took out the coils on the stator, you can get new coils for the stator plate. If you can't the parts you need on that side of the pond let me know and I will see what I can do to help. CBX

[greencannon]

Sounds like serious crank damage. Assuming the bearings are not totaly wasted, If the ends of the crank move up and down ( when in the cases???) then they must be bent, wich would take some serious abuse to cause that to happen. Sounds like someone used a large mallet to SERIOUSLY BEAT the crank out of the cases instead of using a puller and press. Thus causing cases to crack.
 Or someone did a horrible job rebuilding the crank, left it way out of "tru" and ran it till it vibrated the engine so bad the cases cracked.
 Unfortunately I've seen this happen at the hands of an idiot who called himself a professional. Poor KX500 crank....
Bring your crank to a reputable machine shop( preferably one that specializes in motorcycles) and have them measure it up to see if it's salvageable.
 I replaced mine a few seasons ago due to wear at the seal contact point stator side. ( little wear groove on the crank end)
The cost of repairing it would have been ridiculous, I took the hit just replaced it with a new one from Kawi. But before i installed it, had the machine shop tru it up and weld it.Really toned down the vibration and crank seals seam to last forever now.
Good Luck

[dave916]

This is not a common thing, sounds to me like someone had a major piston failure , fixed the piston problem but failed to check the crank. The damage probably happened the first time the motor was refired. Cases can be welded , and the crank should be fixable as for the flywheel , it should be ok but it probably took out the coils on the stator, you can get new coils for the stator plate. If you can't the parts you need on that side of the pond let me know and I will see what I can do to help. CBX

 
was thinking it might be piston failure but the  barrel and head are in good condition except for a small chip on top of main exhaust,the piston had a big piece of skirt missing on exhaust side and someone had filed it and reassembled,
my other though was that some forced the crankcases together when assembley [but the bigend conrod looks worn]
donnt think the motor would run long with the crank that bent
look like some could have changed the coils and left the flywheel
at first i tought it was someone gettng heavy handed removing the fly wheel until i realised the clutch side was also bent
as for welding cases i think the the crankshaft bearing housing are worn [play in -out and no up down play]   
this is the third set of cases i have with worn crankshaft bearing housing[