Cam Bearing Selection And InstallationThe task of replacing camshaft bearings during an engine rebuild may appear to be a no-brainer, but the more intelligent approach is to handle the job with as much planning and precision as you would when replacing main or rod bearings. If not, your engine is likely to wind up with a damaged camshaft and/or main and rod bearings in a relatively short period of time.
"Simply knocking out the old bearings and installing fresh ones with little regard to bearing selection, sizing, or alignment is a big mistake," says Jeff Schaerer, Engine Bearing Product Development manager at Clevite Engine Parts. "For example, ill-fitting cam bearings can result in too little or too much oil clearance, which can damage both the camshaft and/or main and rod bearings. If excessive cam bearing clearance exists, a severe reduction in oil pressure can result in insufficient oil delivery to the rest of the motor."
Mindful of the critical role that proper cam bearing selection, sizing, and alignment can have on engine longevity and performance, let's compare the attributes of two different types of materials commonly used in cam bearing construction. By doing so, you'll be in a better position to determine which type of cam bearings best meet your performance needs.
Bearing SelectionClevite's Schaerer explains that in previous years, the vast majority of cam bearings were manufactured with a "babbitt" lining. Babbitt is a soft, slippery material composed primarily of lead and tin. This soft material does an excellent job of being able to withstand particle contamination and less-than-ideal lubrication on initial engine startup. However, performance engines often operate at higher temperatures and feature higher valvetrain loads, which places babbitt material at a disadvantage. These operating conditions sometimes result in fatigue or deformation (extrusion) of the soft babbitt material.
In order to address higher loads and temperatures, babbitt, for the most part, has been replaced with an aluminum alloy. This specially developed alloy is much stronger than babbitt and can withstand much higher loads. The trade-off lies in the fact that aluminum alloy is harder than babbitt but is less forgiving with regard to contamination, cam bearing bore misalignment, and less-than-ideal lubrication. The benefits of aluminum cam bearings, however, far outweigh the compromises. You simply need to pay more attention to details when installing aluminum cam bearings and be certain to verify critical tolerances.
Traditional babbitt is designed to withstand approximately 1,800 psi of load. By contrast, Clevite's AL-3 material has been designed to withstand up to 5,000 psi. Schaerer says extra oil grooves are not needed with the AL-3 bearings, providing yet another benefit: the bearing affords a larger "footprint" at the cam bore wall, which more efficiently transfers heat away from the bearing. In addition to bi-metal aluminum cam bearings they've also developed tri-metal bearings that combine the strength of aluminum alloy with a babbitt overlay. The tri-metal bearings are able to withstand loads in excess of 8,000 psi.
Cam Bearing InstallationIf you're planning to work on an engine block that has been newly reconditioned, you'll definitely need to replace the camshaft bearings, as the old bearings must be removed beforehand to allow the block to be properly cleaned. The following can be used as a guide for installing cam bearings properly.
The installation process begins after you've accomplished any machining that might be needed (cylinder boring and/or honing, align-honing, deck resurfacing, cam bore alignment, etc.). Before starting, make certain that the block is totally clean. If it's not, then foreign particles trapped between the bearings and bearing bores will cause bearing deformation and reduce oil clearance.