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No yami knowledge here about valves

By drz250vid,
in YZ400F/426F/450F/450FX

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drz250vid

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Did a quick search here and did not see anything about valve problems with these bikes as compared to the red, yellow and green.

Is that so? I ride a two stroke but with the great deals may want to upgrade but i am afraid to blow a top end. How is valve maint on the yz four strokes? They bend or blow often?

new 06 has 5 valves? thanks guys

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suzuki28

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my dad and i had yzf's. he had the 450 and i had the 250f. i rebuilt the topend once on my 250f in 2 years. my dad had his also for 2 years and all he did was ride and change the oil and air filter. like i always say they are the TOYOTA of motocross

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grayracer513

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You're not going to see much in the way of valve issues on this or any YZF forum. Yamaha produces an extremely high quality titanium valve and treats it as well as is possible. The nitride coating is applied as heavily as the current technology allows, and the valve seat materials are matched to the valves very well. There are lots of '03's, and even some '01's that haven't had their first valve reshim yet. And it isn't just the valve train that holds up well, either. The 250F's go through them a little faster, but the cams in those little rev monsters spin faster than the cranks in most cars do, and they end up with easily twice as many valve cycles per hour as the big bikes do.

The 5 valve design means more, lighter intake valves that require less spring pressure to control, and need less lift to provide the necessary air flow. The less aggressive cam profile means that spring pressure can be reduced even further. That helps.

That explains the intakes, but what about the exhaust? There's only two, like everyone else. Just a sound design, executed well from high quality materials. That's all anyone would need.

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drz250vid

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WOW guys! Thanks for the info. Well if that aint enough to wanna go blue I dont know what is! So how far back would you guys go if buying a used 450??

sorry i do mostly trail riding and climbing stuff. i do like to try to get air though and pose as an mxer every once in a while.

racing would be strictly haresrambles

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grayracer513

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All the 450's have been among the best bikes Yamaha has built in terms of reliability. But each year has had it's own "character". The '03 had an ignition map and overall tuning that made it an extremely responsive, torquey, and quick revving engine. It may even have redefined those terms all on its own. That, combined with one of the lowest rotating masses any such bike was ever built with made it a bit of a handful, and somewhat difficult and tiring for some to maintain control of. The stock clutch was a grabby pain in the butt, too. Both these problems are curable by adding a GYT-R flywheel, or the 6 or 8oz Dr.D unit, and the GYT-R clutch plate kit.

The '04 had the same engine, but a different spark map, and was a little better behaved. The clutch had been fixed, but they still benefit from a little more flywheel weight. The forks were new and were a significant improvement.

The '05 had even better suspension, and a much more civilized engine. Some say too civilized, but the thing is still really fast. They just need to be ridden differently. Dynos prove they have as much real power as the '03, but they just don't bring it on quite as hard at low RPM.

You can't go wrong with any of them, really.

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