Single vs. Double Cam?

a have a yamaha and my friend a honda. We talk about the advantages/disadvantages of an extra cam, but it's mostly harmless sh*t talking cuz we really don't understand the science behind it. What's the difference between the two types of engines? :thumbsup: Is one better in certain aspects than the other?

Both designs are essentially the same. They are both overhead valve, overhead cam designs, so they both have the same advantages and disadvantages. The advantages the single cam has going for it is that it is a little lighter, easier to time, and costs less to upgrade to a performance cam (since you only need to buy one). Other than that they are basically the same.

The way that the CRF is made, with the cam and lifter bores in a separable cam tower, makes the head less expensive, which is convenient if you have to replace it.

With the DOHC set up as used in the YZF, the cams act directly on all of the valves. This eliminates any significant side loading of the valve guides. In the Honda, the exhaust valves are opened by rocker arms. The wiping action of the rocker arm at the tip of the valve stem imparts a significant lateral load on the valve, which wears the guide.

With a DOHC, a tuner can freely modify the lobe center split between the intake and exhaust cams without grinding a different cam. Not possible with the CRF.

Rocker arms add reciprocating mass to the valve train that ha sto be compensated for with heavier valve springs.

makes perfect sense. I'm sure I'm not the only one that was curious. What about power delivery? Is there any reason one setup would lead to a snappier engine vs. smoother engine? Does the single cam mean less rotating mass thus more snap? I'm just trying to understand the general concept

The single cam has less rotating mass, but not much, really. The direct acting DOHC setup is simpler and more mechanically efficient in spite of the additional cam.

Neither has any particular advantage in power production. That comes from the ports, combustion chamber design, and the way the valves enter the combustion chamber, rather than what device is used to open the valves.

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