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Yamaha MX & Off-Road Dirt Bikes
YZF Rebuild
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[QUOTE="Rich Rohrich, post: 713868, member: 16241"] The YZFs with steel valves are incredibly robust even when they are revved HARD. Most of the YZF engines I've seen went a couple of seasons before they ever needed a single shim changed. Running WR timing on a YZF is a really BAD idea IMO. There have been a lot of misconceptions about WHY Yamaha set the valve timing the way they did on the WR thanks in large part to our friends in the magazine business who don't understand cam timing. Anyone who does a little research into engine design will quickly discover that the only logical reason for Yamaha to advance the exhaust cam timing so far in the WR was to start the exhaust blowdown early enough to get the engine to run properly across the rev range with the super-restrictive stock exhaust insert . Once that restriction is removed the exhaust valve opens way too early with the WR timing (23 crank degrees too early) and will tend to flatten torque on the low end, and just kill any hope of making top end power because the exhaust closes 23 degress earlier and reduces overlap by that same amount. The only possible value of the WR timing on a YZF is you'll see an improvement in no-load idle quality, other than that don't waste your time with that nonsense. :thumb: So I guess to answer your original question, yes it probably would increase the time between rebuilds. Given that it won't make any real power at high revs, and won't be as much fun to ride you'll probably leave it in the garage more and never wear it out. ;) [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
YZF Rebuild
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