Yamaha WR450 Engine Rebuild

Crankshaft Rebuild on WR450 Fourstroke Engine

Always sad to see an engine in this condition. However, help is at hand and we have the tools to make it all nice and new again.

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"
 
 

01_Im_sure_these_things_have_engines.jpg
01_WR on bench
02_oh_yes_very_sad_engine.jpg
02_very_sad_engine
03_Measuring_web_before_pressing.jpg
03_Measuring_web
04_New_rod_kit.jpg
04_New_rod_kit
05_pressing_crank_apart.jpg
05_pressing_crank_apart
06_Bad_crankshaft.jpg
06_Bad_crankshaft
07_bad_bigend_bearing.jpg
07_bad_bigend_bearing
08_New_crank_pin.jpg
New_crank_pin
09_Final_press.jpg
09_Final_press
10_truing_crank_runout.jpg
10_truing_crank_runout
11_New_main_bearings.jpg
11_New_main_bearings
12_cases_back_together.jpg
12_cases_together
13_New_piston.jpg
13_New_piston
14_new_piston_chrome_barrell.jpg
14_new_piston &_barrell
 

Article on a WR/YZF250 Hotup
Article on a WR450 Hotup

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