125 2001 Kx125 engine tightness

Flanagan

Flanagan

Hello everyone,

I have a 2001 KX125 that has been causing me some problems. About a year ago now, the bike started spitting up a lot of oil from the exhaust, so I figured it needed a crank seal replacement. After removing the engine from the bike I set it all up on a table, got the proper tools for the job and disassembled and installed the new crank seals. Up until this point all was well..
When I went to put everything back together just the way it was before (following the manual) it all fit into place. Now, once the crankcases were back together, I went to turn the crank and it would barely move and was stiff in place. Same thing when I went to turn the sprocket and rod connected to the transmission on the inside of the case. Everything was just tight, as if it was torqued too hard--but this wasn't the case after checking with multiple different torque wrenches-- For several months this has been an issue and mechanics are trying to charge me $500+ to look at it, diagnose and repair, when I know this is an easy fix. So if there is anything that jumps to mind when you hear, "the trans and crank are stiff and won't move smoothly" when the cases are put back together, please let me know in comments below possible resolutions.

Things I have already checked:

-Torques are correct (using a Snap On digital torque wrench and checking with other wrenches to be sure)
-Bearings are fine
-No cracks or bends in crankcase or anything of that matter
-All pieces are properly assembled

I am still considering after all this time that it is possible that I am just making a simple mistake when I disassemble and reassemble the engine (this has happened several times). So it definitely is possible that I am forgetting something or missing something simple that could be causing this stiffness. Please any experienced mechanics or people with general kx125 or other 125 engine experience, comment below possible resolutions to this mystery!

Thank you for reading, Merry Christmas and Happy New Year!
 
Last edited by a moderator:
O

ossagp

If you had the cases apart and then back together you usually get a certain amount of bind when the crankshaft goes back into the main bearings. The simple fix right now is to take a plastic mallet and smack either or both ends of the crank shaft at about a 45 degree angle. Widely used method for relieving the stress by engine builders who squeeze them together. If you want to learn a gentler method of assembly I have that too, but guys that build them for a living using the presses end up having to do that frequently. it also happens when they just go together cold by hand sometimes. So give that a try before you tear down again.

Since you have about a 50/50 chance it will still slobber after you get it running, check back for the fix for that too.
 
SRAD97750

SRAD97750

Moderator
Staff member
Triple check the shims and gears are all in the correct alignment. Case guide/alignment pins can become distorted and can cause binding. It always takes me a couple trys.

I spent a month trying to get my brother's KDX200 to go back together. It would spin freely until the last 1/4 turn of the case bolts. Then the crank would lock up solid.
Baffled, as I have installed quite a few bottom ends, I troubleshot everything under the sun.
In the ~35 failed installation attempts I managed to screw up the threads on one end of the crank.

Replaced the crank with another used specimen from eBay, with new bearings and it installed first try. :noidea:
Must have mangled the original crank/bearings somehow. -BIG DAN:thumb:
 
PALMER84ONE

PALMER84ONE

ossagp:
You guys go to a lot of trouble :smirk::P:smirk:
Click to expand...

Never had the time to talk, type, or text out a long story like you. Hit it with a bigger hammer and you get the job done faster.

2strokesteve89:
did you replace the paper gasket with gasket maker? if so just the difference of the thickness of the gasket could cause the crank to bind. at least it does on my RM.
Click to expand...

There is a paper gasket between the halves?
 
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