Just a thought........ Honestly what do you owners of these bikes or anyone else for that matter think of the reliability of the motors? Cannondale had some connecting rod big end bearing problems, or maybe lack of oiling, but it revved to the moon also. In ATV applications for the general public, do you think the reliability of valve springs and all other moving parts are going to be good? Obviously those of you who bought one sure hopes nothing will give problems. But take a motor that has cams, chain,and 5 valves and springs, all combined with the high RPM, how can we expect the reliability to be better than a 2-cycle turning less than 9000 RPMs? I am just curious on what others think about this. I know time will tell the tale, but this is for discussion. I DONT WANT THIS TO BECOME ANOTHER 2-CYCLE VERSUS 4-CYCLE WAR!

 

i understand your concern over reliability with such a high revving motor and extra parts over a two stroke. but you have to remember that this motor design has been out since 98 when yamaha came out with the yz400f dirt bike, and if you search the web and asked the owners of these bikes, you'd find the majority of owners have had many trouble-free miles on these engines. there's also all the experience yamaha has had with these 5 valve motors since 85 or so (correct me if i'm wrong) when they came out with the design on their street bikes. i own a 98 yz400f bike and have no problems with the motor, even after installing a bore kit. the majority of the problems with these motors seemed to revolve around the cam chain tensioner and con. rod bottom bearing on bikes with a lot of miles. if you keep fresh oil in them, clean the filter, and adjust the valves they will last a long time. i would be more worried about the yfz frame and a-arms instead.

 

I'm not at all concerned w/ any aspect of the 4-stroke. I ride my '03 Honda CRF450R like I stole it and have never had any sort of internal problem - hell, I've never even seen the spark plug. There are more moving parts associated w/ 4-strokes, but the ricer burners are very dependable. I broke my 13:1 piston in dragging the bike up Sand Mountain. I had just taken delivery of the bike (2) days prior. I ride that quad very hard - the only way in the sand.

The question I have is what advances are we to expect w/ 4-strokes in the future? How outdated will the performance of my bike(s) be in (3) or (4) years?

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