Why do you need to "degree" a cam?

[chevynut]

I just watched this video by Comp Cams and it looks to me like the only reason you need to do it is to make sure they ground the cam correctly. Seriously? You mean you can't trust a cam manufacturer to make a cam to their own specs?

http://www.cpgnation.com/forum/threa...camshaft.7553/

[Rick_L]

The direct quick answer to your question is yes.

The first thing you are verifying is that the camshaft was not mismarked and mispackaged. In other words, verifying you got what you ordered instead of the wrong cam in a box that says it's what you ordered. or maybe a cam that got marked wrong. (Usually an aftermarket cam has some sort of code stamped or more often hand engraved on the front of the cam.)

The second thing you are verifying is that the cam's opening and closing spec are phased correctly to the crankshaft rotation. What you're really checking here is whether they machined the location of the dowel pin that locates the timing gear correctly relative to the cam lobes. Believe it or not, that's the most common error you'll find when checking a cam - it's either advanced or retarded relative to either "straight up" or whatever the cam card says. Usually a cam is machined (and the dowel pin located) so that the intake and exhaust events are symmetrical about top dead center of the piston. The other common situation is that the camshaft is machined so that the intake events are 4 degrees advanced from "straight up".

The third thing you could use this procedure to advance or retard the cam events from "straight up" depending on your preference and goals. Advancing the cam in general increases low end torque, and retarding it increases top end torque. Think of it as "rocking" the torque curve about some intermediate rpm. Thing is, you usually wouldn't want to advance a cam that's already machined that way.

All of the above only requires checking the #1 intake and exhaust lobes on the camshaft.

The final more advanced deal would be to check the cam timing on all 8 cylinders, intake and exhaust. This is just further QC but you could also see differences in timing based on how well the lifter bores were machined. This could be a deal if you run valve to piston clearance close.

In my experiences, I have seen a mislocated dowel pin several times. I once had a camshaft from a major supplier that was a "sampler" or "smorgasboard" cam. It actually had lobes of different duration and lift from cylinder to cylinder. I have also seen a couple of deals on lifter bore location. The way you find that is to check two camshafts. If you consistently have a cylinder/valve that's off, it's the block. I've also had a block that had all the lifter bores "corrected" (machined oversize and fitted with bushings) that had the passenger bank retarded from the driver bank by a couple of degrees. If you run the valve to piston clearance really close, cam timing variations affect that.

I know some of my examples are extreme and possibly nit-picking, but degreeing the cam is the way you find this stuff.

[chevynut]

Thanks for the excellent explanation. I understood the procedure, just didn't know why you had to do it. I guess everyone makes mistakes.

[WagonCrazy]

Thanks Rick. I just learned something more here...

[Gregs04.5]

Thanks Rick, very informative. I've seen that explanation, and also crankshaft key errors causing timing problems.
Either way, it's a good thing to check.