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C-legs

Top end rebuild?

12 posts in this topic

Hey guys, new to the forum.

I'm looking to rebuild my top end as suggested by a Yamaha mechanic. I bought my bike brand new in 05 and have been having alot of trouble getting her started while out on the trail.

Ive adjusted the valves already and it didn't fix the problem. I believe Yamaha suggests the top end be rebuilt every ten hours?

So I'm looking for some additional advice, rebuild or not?

I do all trail/desert riding with an occasional trip to the sand dunes here in So. Cal. My bike is an 05 YZ450.

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A rebuild every 10 hours is really excessive unless your an AA or pro racer. If you dont rev the heck out of it, arent jetted lean, and change your oil frequently, you should get 50 hours or so out of a top end.

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10 hours would be quite excessive for a re-build interval. I believe the manual calls for a top-end every 50 hours. That being said, there are members on the forum with 200+ hours on original top ends. It is dependent on how hard you run the bike ie. racing or play-riding.

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yup, but its really hard to say what you need without an idea of hours and riding style. Open her up and ask questions if your not sure. I think most guys do piston, rings, cam chain, valve springs and guides for a rebuild. But could need more ...

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I should be due then. Would a compression test confirm this?

Not on these bikes. You cant get an acurate compression reading on bikes with auto decompression.

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I guess a trip to the mechanic is ultimately my best bet for diagnosis.

Anyone in the So. Cal area LA/OC, that can forward info to a reputable mechanic?

Its been hard to start for some time even after a valve adjustment.

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My first thought for your problem was replace the cam chain. I think that would help your hard starting problem. However, its and 05 and you mite as well replace the piston, rings and wrist pin while you got it down for a cam chain.

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Clean carb, check valves, check timing, adjust jetting....

New top end every ten hours!!:thumbsup::lol::bonk::lol:

Try 100-200:lol:

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Clean carb, check valves, check timing, adjust jetting....

New top end every ten hours!!:thumbsup::lol::bonk::lol:

Try 100-200:lol:

x2 The guy who told you to rebuild every 10 hours probably just wanted your money...

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x2 The guy who told you to rebuild every 10 hours probably just wanted your money...

09 yz450 has 414 hrs and counting. Never opened up and starts 1 or 2 kicks and still runs strong. Run a true synthetic and the motor will reward you.

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Just a little update, I was able to get my bike to a mechanic and as some of you mentioned It had nothing to do with rebuilding the top end and everything to do with the carburetor. :ride:

The mechanic told me he suspected the valves and or the carb were the problem when I handed the bike over to him and mentioned the problems I was having. When I picked up the bike he said the valves were within spec but my carb had a plugged jet and was dirty.

Runs great now, had it out yesterday enjoying the 80* weather So. Cal had to offer. :cheers:

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