When upgrading our LT1 to an LS1-style ignition with the bolt-on kit from EFI Connection, we began installing our camshaft from COMP Cams with the factory cam gear. We found our Top Dead Center and then our Intake Lobe Centerline.
To meet our desired 111 degree intake centerline, the cam core was ground at 115 degree lobe separation angle with +4 degrees of advance. However, with chain stretch and tolerance stack up between the cam gear dowel pin hole and the cam pin, we ended up with a centerline of 113.750. The solution? Clock the cam forward with a degree bushing.
While there are gears out there, we decided to see if we could do it ourselves. With a little planning and access to a mill, modifying our existing gear took less than an hour to complete.
We started by using a .250 gauge pin on the original index hole to center the mill with the hole. We then switched to a 13/32″-end mill bit slathered in Boeing Lube paste and slowly drilled out the hole. The degree bushing fit like a glove.
Since the degree bushing will line the gear up in a new point in rotation, the mounting bolt holes needed to be slotted. For this, we used a .350 or 9mm bit and made our way through the gear near the existing holes to enlarge them into slots.
Our first degree bushing of 6 degrees was a little too drastic at 107.5, causing the piston to valve clearance to be too tight, but a 4-degree bushing put us right at 109.250, which will work great for our application.