How do you fix a bottom end bearing for a 99 rm 125?

The bearings in the connecting rod are meant to be replaced when they wear out, the top end bearing is easy to replace. The piston comes off and the bearing will slide right out of the con rod; however, the bottom end bearing requires that the engine case be split USING THE CORRECT TOOLS (look up "tusk case splitter") as the case is easily damaged by prying the halves apart. Once the crankshaft has been removed from the case, you will have to use a hydraulic shop press to press the halves of the crankshaft apart. The bearing should slide off unless it failed so catastrophically that it has welded itself to the crank. New bearing goes on, con rod goes on, halves of the crank are then pressed back together. The crankshaft MUST be trued using V-blocks and dial gauges, it can't just "look right". If the crank isn't true the vibrations when running will make the bike unrideable at least, at most the engine will actually explode.