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Zik0

Piston

7 posts in this topic

i read that you have to chenge the piston of an 426 every 40 hours?

is this true?

thx! :)

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Maybe if you're a factory rider. I venture to guess that most people (myself included) are way way beyond 40 hours on one piston and still going strong.

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I had an 01 426 with at least 120 hours on it when I sold it and it was (and still is) running fine. Religious oil changes and clean air filters after every ride is responsible for most of that I would beleive.

If I had a big blue semi-trailer it might be a different story :)

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Yea it's something like that. The new CRF 450's have a recomended 15 hour piston skirt relplacment time. But you dont have to do this if you're not a racer. This is so the bikes stay at 100% performence. I got a 2000 426 and i can't feel any compression loss. This is because race bikes come with small skirts on the pistons, rev higher, and perform more. :)

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Let me give you the flip side on this topic. I was a firm believer in leaving it alone if it aint broke don't fix it. Especially for a guy like me who doesn't race, just rides in the woods, and has a 98 400 running fine.

I had to tear it down for a 4th gear failure, while it was down, of course I looked at the piston and rings. Everything measured up GREAT, ring gap was only around .009 in. Took the piston into work and had the materials engineer review it under the microscope. Guess what! New piston. Engineer says the piston was starting to show stress / fatigue around the pin from skirt to skirt on both sides. NO CRACKES, but fatigue lines that really bothered him. Waiting to see what the final analysis is, as he is now sectioning the piston to see what internally is going on.

Long story short, replace the piston at reasonable intervals dependant on your riding style. Six years is way to long, and way too lucky for me. :)

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What he said! Replace the piston at reasonable times. Top end rebuilds are fairly easy since you only have to take the "top end" off and don't really have to take the entire engine apart.

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