I noticed that some of the new 125s have double overhaed cams while others have....well not two. What is the difference in this? Does this affect performance at all? I'm just gettin into learing all about bike motors and was wondering.
THX
~Jamie

Which 125's are you refering to? Double overhead cam's is refering to the fact that there are two camshafts operating the valves. Usually, when you have double overhead cams, its because they are using 4, or even 5 valves, per cylinder. Like the YZF... its dual overhead cam, one cam operates the 3 intake valves, the other operates the 2 exaught valves. (YES, I CAN'T SPELL EXAUGHT) The thought behind it is that the multiple, smaller, valves allow fuel to enter and exit the engine better, hence more preformance. The lighter valves can also therfore sustain rpm better, because they develop less momentum, because they weight less. Single overhead cam usually incorperates a single valve for intake and a single valve for exaught. So double overhead cam is definatly higher preformance. Its also much more complicated to work on. (ie two camshafts to line up when rebuilding, etc. etc.)

I actually misread the captions. They were actaully 250s. My bad. Thank You for all the inforamtion. I'm really learning alot and having alot of fun doing so....I guess its partly because i have more patiance than my dad. :-P
THX
~Jamie

Well, actually, atc3434, you are wrong about the single overhead cam. The honda CRF450 has a Single Overhead Cam, while the YZF450 and 250F have the Dual Overhead Cams. The CRF450 has 4 valves, 2 intake and 2 exhaust. The cam directly operates the 2 intake valves and moves a rocker arm for the exhaust valves, rocker arm moves exhaust valves. The YZF450 and 250 have 2 cams, so one cam operates the intake valves and one cam operates the exhaust valves.
Yamaha and Honda have their reasons for using 2 intake valves(honda) or 3 intake valves(yamaha). There were some threads on which is design, 2 or 3 valves, was a better design for performance. I think the 2 valve design was better for modification, forget why though, try and do a search in Mods & Performance Forum.

Go to this Honda site. http://www.hondamotorcycle.com/moto...odelId=CRF450R4

Then click on engineering on the left, a new window should pop up. Then click on valve train to see a pic and brief desciption of the cam and stuff. This is the picture of the head of the crf450 from the Honda site. Labeled.

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Glitch, good catch on me. I ASSumed it was similar to the YZF style. Good catch! Was the rest of my sumation up to snuff??