Yamaha WR450 Engine Rebuild
This chap wasn't sure why it stopped going, but if you have a look at the pics you'll see why. It could have been a lot worse, just quietly.
Once the cases are separated it's important to measure the web to web (see pic 3) with great accuracy, for when it goes back together if the rod doesn't have enough side clearances it will be back with the same problem very quickly. You need a good press to push it apart and make sure you're not standing to close in case something flies out.
Putting the new rod kit in is very tricky - I have seen guys damage rods pressing things together incorrectly. Once it's together and the conrod side clearance is spot-on then it needs to be trued to within .05mm at the end of the shaft, that is both ends.
See pic 10, there's a big copper hammer there ( I like to call it my persuader), because we hit the web to move it all into place. Ever seen those medical shows where surgeons are drilling and hammering, it looks rough when in fact, done correctly its very accurate. Again this is very precise work, one wrong move and it's all over, very important to get the run-out within .05mm to ensure long life and minimal vibration. This job is best left to the experts.
Crankshaft main bearings are replaced - they also need to be carefully pressed into place, along with the crankshaft, then you can fit the cases together make sure the crank is not stressed. Always make sure it turns freely once the case are bolted together, if it doesn't pull it apart, check everything and start again.
/ "feel the difference"
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