YZ450 Rebuild time?

7 replies to this topic
  • PimpdYZ

Posted January 01, 2005 - 06:55 AM


I just acquired an 03 YZ450 :cry: and was considering a top-end rebuild. The previous owner told me that he had about 100 motos (15 min--total running time 25min per race) on the motor with only wrist-pin and cam chain replaced. The valves were still within specs and there has been no significant loss of power.
What should be my plan of attack to prevent my motor from self-destructing. :cry:

Am I even due for a rebuild yet?? I do not have much money to spend on rebuilding the motor right now, so what parts, if any, should be replaced?

I read the latest article in Dirt Rider magazine by Eric-Gorr... I seem to think that his recommended service intervals are rather short.. Any Opinions...

Thanks for the advise..
Matt :cry:

  • Indy_WR450

Posted January 01, 2005 - 07:56 AM


If you replace the chain you got to replace the left side crank with the timing chain sprocket. It is a small sprocket that wears quickly and rounds its teeth.
So you might as well then split the cases and replace the counter shaft seal and pop in new crank bearings and rod bearings. :cry:

  • MXKyle

Posted January 03, 2005 - 05:12 AM


I just did a top end on my 450 over Xmas vacation. I took my time and it took about three hours. I had about 150 hours of MX on the bike over two years. The valves were still in spec and didn't need adjusting and the piston ring's end gap was still in the service limit. I put the new stuff in anyway because I plan to sell it and buy an '06 when they come out nad there was no sense in taking the bike apart again in a couple of months. The motor did seem a little less noisy when I broke it in on Thursday. But that may be wishful thinking.

If the previous owner of your bike kept the oil changed, as I did, the motor probably doesn't need much. The YZf seems pretty bulletproof.


  • PimpdYZ

Posted January 03, 2005 - 06:57 AM


I am new to this type of motor so its good to hear that the YZ450 is pretty much bulletproof. :cry:

-- All fluid changes were done with Yamaha factory fluids on a regular basis. --

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  • 642MX

Posted January 03, 2005 - 11:31 AM


I'm still on the factory piston and rings, my valves haven't needed adjusting yet either. I bought mine new in Dec. of 2001, I'm starting to think maybe its time for the top end, but it still runs too good.

  • Wayne_Thompson

Posted January 03, 2005 - 01:54 PM


I just rebuilt my top end a few weeks ago. It had approx. 700 miles on it and I change the oil every 5th ride. Everthing was in good shape other than slight wear on the crank. I plan on replacing the crank on the next rebuild sometime near the end of the year.

  • Asrith

Posted January 03, 2005 - 11:08 PM


Can anyone tell me what a topend rebuild might cost? I just purchased this yz400 and the previous owners brother crashed it and the decomp lever somehow affected it from not being able to kick over(rambling), I am wondering what you all think a good estimate of a topend would cost.

  • MrMotorhed

Posted January 07, 2005 - 03:22 PM


most people are in denial about how much maintenance any bike needs

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