Hi, I have owned a few 400ex's and sold them all off and have now started building up a different quad. I bough a 2003 400ex bottom end that the chain busted a hole in the left crankcase. I have bought the new left crankcase on ebay. And I am planning on splitting the case and installing everything into the new case and reassemble.

I am a master certified auto technician and have done tons of mechanical work on atvs, BUT the one thing I have never done is split the case on a atv engine. I know the bearings are pressed into the side cases and will need to be pulled apart, my question is. Are there any tricks to this that the service manual don't address? How hard is it to split the case. Will I need the special puller or will I be able to be carefully tap it apart with maybe the aid of a hairdryer on the case around the bearings to expand the aluminum. Any tips or special tricks would be very much appreicated. And yes I have a factory service manual coming in the mail. thanks for all the help. mike

also can I just leave the right side of the engine together and just remove the left side cover then the left crankcase and install the new crankcase and reassemble or do I have to strip both side cases off. thanks

 

first dont hit the crank with a hammer. a hair dryer wont touch the bearings if they are stubborn. Just put the case in the oven and they'll drop out.

splitting cases on the 400's are easy just take your time and pay attention to how things come apart. Pay special attention to the transmission. especially 2nd and 3rd gear. Make sure the cogs arent rounding off on the slider gears also

 

You will need to take everything off both sides of the engine. I'll have to check my service manual tomorrow but if I remember right, when you split the cases you will want the tranny to stay in the left side.