Degreeing a roller cam

[philminotti]

I bought a Comp Cams degreeing tool as shown in the photo. It seemed like a convenient little device, as using a magnetic base dial indicator on an aluminum block is frustrating. The chewing gum and duct tape are hard to get off. Anyway, this device fits in the lifter bore. It comes with two cam followers, one for a flat tappet and one for a roller. The follower for a roller cam is a solid piece of metal with a hemispherical profile.

As I went through the process, I encountered some difficulty. Finding the intake center line was no problem, as you just need to find the point of maximum lift. However, when checking the valve events at 0.050, I was getting discrepancies of between 3 and 5 degrees as compared to the cam card. A three degree variance on the intake valve closing point can have a major impact on the DCR, so I was concerned.

Before getting too bent out of shape though, I decided to use a checking fixture that threaded into a head bolt hole and one of my Crane roller lifters. Lo and behold, the discrepancies resolved. It seems that when degreeing a roller cam, one should use a roller lifter and not a cheesy substitute. Go figure.

phil

[RICK LAKE]

philminotti Phil was the cam built straight up or was there a 4 degree advanced in the cam? My crane cam was 4 degrees advanced and I retarded it 6 degrees, great torque. Rick L.

[philminotti]

Hi Rick-

My cam is ground 4 degrees advanced. It's spec'd to be installed with a 108* intake centerline. I ended up putting it at an ICL of 106* to get the intake closing point at 52* ABDC, which is where I want it. Like I said in my above post, using the same ICL of 106*, the Comp Cams checker that I originally used gave me an intake closing point of 56* ABDC. When I switched to using an actual lifter as the cam follower, the ICP dropped to 52*. Interesting.

phil