Motorcycle Repair: Crank freezing up, mix ratio, misalignment

Question
I bought my son a New 2004 Honda CR125R two stroke (forgive me if I sound like a fool but I really don't know much about bikes :)  The crank fouled so we bought a new crank and replaced it.  We did not change the bearings because they did not need to be replaced.  He wrode it at the track and the crank seized again but this time it fused/welded the bearing to the crank.  We had to have the bearing cut off and the crank re balanced.  We put the crank back in this time with new bearings and it does not turn freely.  It seems once we tighten the case bolts down it gets hung up on something but when they are left loose the crank turns freely.  I am at a loss and wonder if there is something my son is doing when he rides that keeps blowing cranks or maybe he is using the wrong oil.  We go to the cycle shop and purchase only what is recommended for that bike and he is carefull about the mix ratio.  Can you offer any advise or insite to our problems?

Thanks a million

Suz

P.S..  I am not being a pest but we are also trying to make it to a race this Sunday so any advise you can offer would be greatly appreciated.  :)  

Answer
Suzanne,

You should absolutely NOT have to replace a crank in an 04 unless this bike has been raced relentlessy for three years and pounded on!

There is a deeper problem here.  It is not anything your son is doing as long as everything is put together correctly and fluids are valid.

It sounds to me you have a bent, mishapen, warped, or general misalignment going on in the engine cases, bearing races (where the bearings sit) or other.  This is why when you tighten the case bolts, the crank won't turn.  

Some bikes have serious issues like this and it can be a factory fault or usage damage.  

I don't recommend replacing everything again - nor do I recommend racing this sunday on a bike that can't be trusted.  If the motor fails on the face of a jump this can be very dangerous.

Your Options...
1) Upon confirmation of my suspicions, replace all affected parts - this can be engine cases, and all else..this can be very expensive.

2) Search ebay for a replacement motor - cr125 motors are a dime a dozen and easy to find for cheaper than you've already spent!!

3) Sell the bike

Good Luck!

Anthony
'Ride Today - Live Again'