Just as a block's main bores can become out of round or misaligned (creating the need for align-boring or align-honing), the cam bores can be subjected to similar geometry changes. This is why camshaft fitment problems sometimes occur when dealing with a used block. However, with a little patience and a close attention to detail during the cam assembly, you can readily overcome such problems.
Correcting Cam Bore AlignmentIf the cam bores need to be aligned, it is possible to enlarge them to establish bore roundness and front-to-rear bore alignment. However, remember, when you enlarge the cam bores, you will also need to address the difference created by the larger bores. This is accomplished by installing oversize-o.d. cam bearings or by sleeving the larger bores to accept standard o.d. bearings.
Due to the popularity of the small-block Chevrolet engine in performance applications, Clevite offers special oversize-o.d. cam bearings that permit align-boring the block's cam bores to one size (matching the No. 1 cam bore, which is the largest cam bore in the block). These oversize-o.d. cam bearings are available in both +0.010- and +0.020-inch sizes.
Clevite's SH-1352S cam bearing kit includes five bearings that are all the same size. Blocks must be bored to 2.029-2.031 inches (0.010 inch larger than the original No. 1 cam bearing bore). The Clevite PN SH-1401S cam bearing kit includes a +0.020 inch oversize, requiring cam bores to be bored to 2.039-2.041 inches.
In addition, Clevite offers a third cam bearing option for small-block Chevrolet engines, PN SH-1528S. These are special tri-metal bearings that feature a +0.010-inch oversize o.d. for cam bores that have been enlarged to 2.029-2.031 inches. These premium tri-metal bearings, though priced higher than aluminum alloy bearings, offer a thin electroplated babbitt overlay for improved bearing surface properties in combination with the high strength of aluminum alloy.
Installing The CamshaftOnce all of the cam bearings have been installed, you're ready to tackle the job of placing the camshaft into position. If the camshaft is new, it is usually safe to assume that the shaft is straight. However, if you plan to install a used camshaft, be sure to check it for runout. Begin by resting the camshaft on its front and rear journals, on clean V-blocks. Next, place a dial indicator at the center cam journal. Preload the gauge at about 0.050 inch, then zero the gauge. Slowly rotate the camshaft a full 360 degrees, noting the runout on the indicator. "Generally speaking, if the cam shows more than 0.001 inch of runout, it should not be used, because the slightest bit of runout beyond this point will likely create a fitment problem," says Schaerer.
Remember to clean the camshaft thoroughly before installation. Cleanliness is critical, so take your time, making absolutely certain that the camshaft is clean and free of any foreign particles.
The next step is to coat the cam, using the type of camshaft assembly lube specified by the camshaft maker (this is often included in a camshaft kit). "Coat the whole stick," says Schaerer in reminding us to apply the lubricant to the entire camshaft, including the cam gear, journals, and lobes.
Now you're ready to install the camshaft. Keep in mind that it is very fragile. The camshaft must be inserted slowly, taking care to avoid dragging the lobes across the bearing faces. Any scratches or nicks can result in unwanted escape paths for oil, which will lead to insufficient oil pressure at the cam bearing locations. It's advisable to use a special camshaft installation tool to ease this task. The tool attaches to the cam nose and provides a convenient handle to help in guiding the cam into the bores while maintaining better control of the cam angle.