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05 engine rebuild

3 posts in this topic

Hey all.  I am in the process of tearing down my '05 WR450 engine.  The engine seized on me while riding.  My fault, after it seized I realized that the oil plug high on the frame was gone.  The only thing I can figure is that I didn't tighten it well after an oil change.


So I figured I would get all the top and bottom end parts, and hell, the bike is nine years old with a lot of hours so I have a brand new bike after the build.  I have the new crank assembly, bearings, piston, and gasket kits.


I have the engine out of the frame and I have the head and cylinder off.  I realized that the piston was my problem.  I guess the oil starvation caused the piston to come in contact with, and weld itself to the inside of the cylinder walls.  Once I knocked the piston down enough to lift the cylinder off of the case the crank actually moves quite freely.  I am confident the seizure was the piston/cylinder union.


I cleaned the piston shrapnel off of the inside of the cylinder wall and it all came off beautifully but I do have a small (less than the diameter of a BB) hole in the cylinder walls.  So I know that these cylinders at NikSil right?  What options do I have there save buying a new cylinder?  Can it be replated or even steel sleeved by like LA Sleeve?


I am going to finish the bottom end rebuild.  I want to see everything inside there is OK, plus I have the new crank and bearings anyway.


What else should I (reasonably) look at doing?  The head is mostly what I'm curious about.  What could the oil starvation have done to it?  It looks absolutely fine.  Even outside the oil issue, on a nine year old bike what would you do?  I would rather not shell out the money for brand new valves but how far should I take it?


What else am I missing on a full motor rebuild?  I've done a fair share of top ends on 2 strokes, but like many jumping from 2 strokes to 4 strokes I'm finally at the "4 strokes are more complicated and more expensive that 2 strokes" part of my riding life.  I will never go back to a 2 stroke again!  I love my WR, I just want to do this right.  Hopefully without breaking the bank.

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Typical oil starvation damage order:


- exahaust cam journals (head)

- exhaust cam races (cam)

- intake cam journals

- intake cam races

- Piston/rings/wrist pin

- Cylinder damage from piston expansion

- cam chain (replace it regardless)

- cam chain tensioner (replace it regardless)

- Crank bearings

- trans primary shaft/gears


You need to plasti -guage the cam/journal mating surfaces in the head to see if the cam journals are still 'round' and not oval. Visual inspection will reveal a lot.

The crank is probably fine. Check your oil and filter for gold dust/flakes, as that will tell you if the crank is begining to fail.

I would replace the cylinder with a new one. They are not that expensive, at 330.00

Edited by Kah Ran Nee

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Ok, thanks that gives a great place to start.  I'll take a much closer look at the head for sure.

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