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dmoney1074

Topend feshen up???

10 posts in this topic

I think i want to do a new piston kit on my 426 just to be on the safe side. Besides the new parts like the pistion rings etc. what do i need to do? I will check and adjust the valves as needed, but do i have to rebore, or re-leeve the cylinder? Or can i just throw the piston in and call it a day? Thanks!

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Measure the bore to be sure it is still in spec for size, out of round, and taper. If it's ok, just slap it back together. If not, you're either going to have to send that cylinder off to have it re-plated, get a new cylinder, servicable used cylinder (think e-bay) or a big bore kit (luke's racing has about the best price around...and it's just about as cheap as sending your cylinder off to get replated, buying a piston kit and gaskets!)

While you've got the motor that far down, I would also pull the head apart, take a really good look at the valves and seats, measure the guides and stems (replace any that are worn out of limits), and put in new valve springs and seals. The springs are only about 5 bucks a piece at the TT store, and are good insurance. Take a look at the cam drive sprocket on the crank (behind the ignition rotor) and replace the cam chain. Clean all the carbon off the combustion chanber and exhaust port while you're at it, and if you haven't already done it, throw in an 03 autodecomp cam and you should be good to go. If you don't go the big bore kit (which comes with gaskets), be sure to replace the head and base gaskets, too. Sounds like a lot, but it's a heck of a lot cheaper and less work than a complete rebuild after you bend or drop a valve, or jump a tooth on the cam chain and smack a valve on that shiny new piston! Oh, and the Wiseco forged pistons are a little noisier than stock (forged pistons are set up to run a little looser clearance), but cost about the same and will last a while longer.

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I've heard of people using a scotchbrite pad to freshen up the cylinder bore... is this nessesary if the cylinder still looks ok??

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I've heard of people using a scotchbrite pad to freshen up the cylinder bore... is this nessesary if the cylinder still looks ok??

Maybe on a cast iron bore or sleeve, but scotchbrite won't make a dent in the Nicasil coating on these cylinders. If the bore is in spec, run a glaze breaker hone thru it for a couple passes to freshen it up and give the rings someting to bite during break in.

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Maybe on a cast iron bore or sleeve, but scotchbrite won't make a dent in the Nicasil coating on these cylinders. If the bore is in spec, run a glaze breaker hone thru it for a couple passes to freshen it up and give the rings someting to bite during break in.

What it that???

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What is "what"?

A "glaze breaker hone"... maybe thats what some people use scotch brite for... to get through the glaze on the cylinder... that was my original intention when I asked about the scotch brite. Of course you can't use scotch brite to hone a cylinder, but maybe to tkae the glaze off???

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I just had my '03 WR450f rebuilt. At 132 hours, it was time. The valves were starting to mushroom and the piston has a wear pattern on the skirt.

I replaced valve springs, keepers, guides, and the valves themselves. I also did a piston/rings and a cam chain.

I now feel comfortable pounding this bike for another 3 years.

These are not old-school 4 strokes and they need care and feeding.

Toes in and on the gas.....

Chad

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Birdy426 When replacing the valve guides do the new guides need to be reamed to size or do the OEM guides fit correctly after install?

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Birdy426 When replacing the valve guides do the new guides need to be reamed to size or do the OEM guides fit correctly after install?

I'm embarrased to say that I don't know...I picked up a head from Eric Gorr that already had the guides replaced and seats cut...The shop manual doesn't say anything about reaming them to size, so my gut feel is that they come sized to be right after they are pressed in. Greyracer, can you add anything?

dmoney- A "glazebreaker" is just a ball hone with very fine grit.

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