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yz400fsmasher

426 crank?

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i got a 98 yz400f and i want to get a big bore but havent found any for the 400. i found out that i could get a 426 crank and get a 444 big bore kit. has anyone done this? and would i have to make mods to the 400 bottom end?

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The only mod you would have to make is to replace the balance shaft drive gear and primary drive gear with the crankshaft. R/H side gears are splined tot he shaft on 426's, not keyed like the 400s. Other than that, it's a simple swap...even the hads are the same. Check with Luke's racing and Eric Gorr's Forward Motion, though, as both used to offer 420cc big bore kits for the 400s.

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The primary drive gear is the same. Only the balancer drive gear is affected by the upgrade.

which gear is the primary gear? the one on the balancer? Im planning on replacing my crank with the 426.

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The primary drive gear drives the clutch. The balancer drive gear is the gear on the crank that drives the balancer driven gear, which is on the balancer.

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