Maintenance & Technical > KX500 Original

Bad crank seal after only four rides.

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Purpletj:
I did a complete engine rebuild a couple months ago. I had her running great and now she is puffing like a train and fouling plugs. I know the culprit is the clutch side crank seal.  I have never heard of them going bad so soon. Anyone have and suggestions when I pull this beast apart again.?

Goat:
I would make sure the crank isn't beat up or gouged where it goes through the seal. Could have even been the smallest grain of dirt. Wouldn't take long to tear a seal apart. May have not been seated right behind the bearing all the way, Slightly crooked will wear it out. Check for any debris when you drain the oil as well. Hope this helps.

no sub for cubes:
i had similar story,when i bought my 500 it was supposed to of been rebuilt,ran fine a few rides then same issues,when i rebuilt it myself i used case sealant on the crank seals,just a suggestion when you put your new seals in might just help seal them properly in the cases.

dave916:
check the crankbearing houses in crankcases, at the moment i have 3 set of cases with them worn
if you cases come apart to easy and bearing stay on crank could be a sign , i usual check engines with the topend removed i try and move the crank left/right with a flat screwdriver
 can be hard to see with engine fully striped as bearing may only be  loose when fully pressed into cases
also check the cases to make sure they are not warped or have any cracks  where tranny oil could also enter the motor
dont forget to put suitable grease on lip of seal  
good luck with the build

Purpletj:
Here is a little more info. I have the engine out now and pulled the jug off. There is atleast 2 ounces of oil in the bottom of the crank case. I am beginning to think when I did the full engine build I may have run the case sealant thin behind the crank. I'm second guessing myself on the crank seals and think this is not my issue,. As I tear more into it tomorrow I will keep everyone informed.

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