March - April 2014 Motor State Performance Report Article By Jim Kaekel, Jr.
Steel-jacketed, needle roller cam bearings not only increase the durability of many high end racing engines, but add a few horse-power as well. Traditional steel-backed, lead Babbit cam bearings may be fine for most racing applications, but they are not well suited to the ultra-high valve spring loads common in maximum endurance racing and can only endure so much load before they ultimately fail. Although the initial cost can exceed several hundred dollars, primarily due to added machine shop labor, needle roller cam bearings offer several important benefits that can help offset the expense. A steel billet camshaft is also required as a conventional, cast flat tappet camshaft is not compatible with the surface hardness of the needle roller bearings.
One of the most important benefits is that the needle bearings can easily handle the extreme loads generated by high pressure, roller valve springs because of their increased load capacity. Also, because needle roller cam bearings require only splash oiling and lack oil delivery holes, oil flow through the cam bearings is eliminated, improving flow to the main and rod bearings. This benefit is two-fold since oil draining from the cam bearings and falling directly onto the rotating assembly is eliminated, reducing oil aeration and windage losses which cost precious horsepower. Lastly, internal engine friction and oil temperatures are reduced with roller cam bearings because of their free-rolling design.
Bearing installation is a bit involved and requires several important steps. Consulting with a trusted engine builder and reputable camshaft grinder prior to performing any machining operations is a necessity since the cam journals must be compatible with the I.D. of the needle roller cam bearings. A custom ground camshaft, or machining of the cam journals of an existing camshaft, may be required as well. A cam bearing set must be selected that is compatible with both the engine block and camshaft. Importantly, the cam bearing I.D. must be larger than the O.D. of the cam lobes so that the camshaft may be installed into the block.
Several suppliers including Comp Cams, Dart and Ford Racing offer the specialized bearings for popular high performance engines. Comp Cams offers a kit (COM350RCB-KIT) that is engineered for small block Chevy and small block Chrysler 360 applications, while Ford Racing has kits for the small block 302-351W (FRDM6261-C351), 351 SVO (FRDM6261-D351) and big block 429-460 (FRDM6261-A460) engines. Dart has roller bearings as well for their own blocks fitted with 55mm camshafts (DRT32220042).
A reputable, high performance engine shop is recommended for the necessary machining operations. The process begins by precisely align boring the cam bearing bores to the specified dimensions. Any oil grooves that are machined away during the process must be restored. Some blocks may also require that the inside of the cam tunnel be machined as well to allow bearing installation.
After all machining operations are completed and the block has been thoroughly cleaned, the bearings may then be installed using a specialized roller cam bearing installation tool, such as the unit offered by Comp Cams (COM5412). The tool kit allows bearings to be installed in most engine blocks and includes a draw bar, swivel handle, alignment head and 50mm bearing head. Additional bearing heads are also available separately for 47.64mm, 55mm and 60mm. The bearings may also be removed and re-installed as required during engine rebuilds.