Cam question?

[threewebers]

Why do the cams have lobes that are narrower on one side than the other ?I have been looking at waynes book but I cant find where its explaed in the book ,It just tells you not to mix up the left from right? Thanks!

[Eagledriver]

I've never noticed this. I doubt there is a reason for the difference other than different batches have different widths. Left and right cams are different since they both turn the same direction but are on opposite sides of the engine.

-Andy

[cgarr]

One cam May have been changed at some point? I know the 912 engines used both a wide or narrow lobe cam, the wide was always preferred.

[2.70Racer]

threewebers,
I think you are asking why there is a right and left side cam.
The right side cam with the lobes somewhat pointing closer together than the left side which point over 90 degrees apart.
I believe Bruce Anderson described it as the right side point up together much as Rabbit ears, whereas the left side by comparison are much further apart forming closer to a L.
As viewed from the back of your car looking in the engine compartment, the engine rotates clockwise.
Since the cams are driven from a secondary shaft by gears, both cams rotate counter-clockwise at 1/2 crankshaft speed.
On the right side as the cam lobes approach the rockers they see the exhaust rocker first then the intake rocker. Therefore the exhaust lobe leads the intake lobe by a small amount.
Remember at overlap the exhaust is almost closed as the intake is beginning to open.
So on the right side the exhaust and intake lobes would be rather close together.
On the left side the cam lobes see the intake rocker first then the exhaust.
So for overlap to occur properly on the left side the exhaust lobe must be significantly advanced as compared to the intake lobe.
At overlap the exhaust is coming off the exhaust cam lobe while the intake is just beginning to rise on the intake lobe.
If you look at the side views of a 911 motor this may be easier to visualize.
If the right side cam turned clockwise, while the left side still turned ccw, it would be made the same as the left side cam. They would be interchangeable.
Conversely if the left side turned clockwise, while the right side turned ccw, the left side cam would match the right side cam.
Right, clear as mud.