Kx250 1994 bottom end build… help!!

[Murch1995]

Hi guys, I’m rebuilding my kx250 1994 bottom end, due to crank seals failed as to my knowledge is a common issue with the kx250 I maybe wrong?… anyway split cases and replaced bearings with hot rod transmission bearings and koyo crank bearings, reassembled the cases and everything was free up until when I tighten the bolts the crank begins to bind I can turn it by using the fly wheel side but doesn’t spin great by just the rod measured the bearings in comparison to old ones before I fitted and were the same, crank isn’t new but was replaced last year haven’t don’t a lot of riding since also it isn’t out of spec, is there normally some drag or do I need to tear it apart again?? Just to add I’ve use th case skitter and. Crank installer tool as required. A family friend said to hit the ends of the crank with a mallet or dead blow to seat the bearings?? And also put some 2stroke oil down the holes to the crank bearings to help lubrication?! And advice would be great thank you 🙏

[KXDINO]

sounds like crank bearings are not seated in the cases all the way.

[jamesohoh7]

I realize this is an older'ish post, but just in case... and/or maybe it helps the next guy with the same issue...

I 2nd the primary cause likely being one/both crank bearings are not seated.  Been there/seen that.

However, also check the side-clearance of the crankwheels to the case (assuming you still have the case bolted together).  There should be very nearly equal clearance on either side.  If one side is very tight, it'll rub and tear stuff up.  This is usually caused by the opposite side bearing not being seated (which offsets the whole assy in the cases). 

It -may- (rarely) be caused by the crankwheels themselves not being pressed on to the crankpin equally.  The crank is 3 parts... a pin with the bearing and rod and two wheels, pressed onto that pin.  If one wheel is not pressed on all the way, it'll be tight against the case when assembled.

There's probably a spec for overall crankwheel width (ie., outside edge of crankwheel to crankwheel, across the rod-gap).  Measure that to make sure its where it should be.  If its too wide, you may need to go back to the vendor and see what they can do for you.