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C1 July Cover.indd c1 7/22/15 10:29 AM Bearing Selection and Cam Bearings Cam Installation

By Gregory Jones, Managing Editor [email protected]

eplacing bearings than babbitt and can withstand production semi-finished cam during an engine rebuild is much higher loads. The trade- bearings are put in the block and Ra no-brainer, but don’t take off lies in the fact that aluminum line-bored into place to eliminate the process lightly. The intelligent alloy is harder than babbitt but any tolerance stack that you would approach is to handle the job with is less forgiving with regard to see from the housing geometry as much planning and precision as contamination, cam bearing variations. you would if replacing main or rod misalignment, and less-than- “When you pull the factory bearings. Simply knocking out the ideal lubrication. The benefits of bearings out you need a close old bearings and installing fresh aluminum cam bearings, however, tolerance bearing to get the proper ones with little regard to bearing far outweigh the compromises. oil clearance since the blocks aren’t selection, sizing or alignment You simply need to pay more really made for finished bearings,” is a big mistake. Ill-fitting cam attention to details when installing McBroom says. “You need to bearings can result in damaging aluminum cam bearings and be have real close tolerance on the both the camshaft and/or main certain to verify critical tolerances. components going in. In the case and rod bearings. Cam bearings are usually of the high performance bearings, available in a range of basic they are held to 0.004˝ tolerance, Selection bearing constructions. One is a and the OD is held to 0.001˝, which In previous years, the vast standard babbitt bearing, another will give you better control over majority of cam bearings were is a high-performance bearing, the oil clearance – that’s important manufactured with a babbitt and the third is an even higher- in high performance.” lining. Babbitt is a soft, slippery performance Teflon-coated bearing In some of the variable valve material composed primarily of with some of the closest tolerances timing (VVT) and V-type lead and tin. This soft material on the market. blocks, oil clearance is critical to does an excellent job of being “In a stock engine you get the proper operation of the able to withstand particle would run a standard babbitt VVT. McBroom says that, in some contamination and less-than- bearing. If it’s high performance, cases, it could be advantageous to ideal lubrication on initial engine high RPM and high valve spring run a high performance bearing in startup. However, performance loads you would need the high- a passenger car if the tolerances are engines often operate at higher performance bearings,” says Bob such that your oil clearances are temperatures and feature higher McBroom, VP of engineering and out of spec. loads, which places manufacturing at Dura-Bond When an engine has marginal babbitt material at a disadvantage. Bearing Company, Carson City, lubrication, such as during start These operating conditions NV. “For increased fatigue strength and stop, the Teflon-coated sometimes result in fatigue or and extra protection against dry bearings reduce the friction on that deformation of babbitt bearings. starts and alignment problems, marginal lubrication regime and In order to address higher loads you’d run the high-performance, when you reduce the friction you and temperatures, babbitt, for the Teflon-coated bearings.” don’t generate as much heat that most part, has been replaced with Cam bearings for cam and block can damage an uncoated bearing. an aluminum alloy. This specially applications are a replacement In general, camshaft bearings developed alloy is much stronger item. Normally during factory can suffer from overloading,

22 July 2015 | EngineBuilder

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oil starvation, misalignment and the bearings and bearing bores will contaminated oil. The possible cause bearing deformation and failures are material fatigue, reduce oil clearance. excessive wear, seizure and Before installing cam bearings, corrosion. If any one of these things wipe all cam bores with a fast-drying occur, you’ll need to replace the cam solvent to create a clean and dry bore bearings. surface. Installation of cam bearings into the block must be done carefully Installation to avoid shaving material from the If you’re planning to work on an outside diameter of the bearings. engine block that has been newly This can easily cause a buildup of reconditioned, you’ll definitely need excess material between the bearing to replace the camshaft bearings, as and the block’s bearing bore, which the old bearings must be removed will “squeeze” the bearing, resulting beforehand to allow the block to be in oil clearance reduction at the Possible failures of cam bearings are properly cleaned. bearing inside diameter. material fatigue, excessive wear, The installation process begins According to McBroom, you’ll seizure and corrosion. These will require replacement. after you’ve accomplished any want to have the proper installation machining that might be needed tools and keep the alignment close “If someone is doing a quality ( boring and/or honing, when you drive the cam bearings in. rebuild, they would have to go in align-honing, deck resurfacing, Make sure the oil holes are lined up. and check the size and alignment cam bore alignment, etc.). Before Also, you’ll need to prep the block to of the bearing bores and the starting, make certain that the block make sure there are no sharp edges, block,” he says. “A lot of times is totally clean. If it’s not, then and if so, chamfer them prior to they’ll go through and do the full foreign particles trapped between installing the bearings.

Circle 23 for more information EngineBuilderMag.com 23

222-242-24 CamCam BearingBearing Installation.inddInstallation.indd 2323 77/22/15/22/15 110:380:38 AMAM Cam bearings are usually available in a range of basic bearing constructions. One is a standard babbitt bearing, another is a high-performance bearing, and the third is an even higher-performance Teflon-coated bearing.

machine work on the block only to find out that there is something wrong with the bearing bores at the OE level. They can have some blocks that are out of spec and some that are out of round. That doesn’t really matter at the OE level, but checking that before you spend any money rebuilding the block is sometimes advantageous.” McBroom also advises that on some blocks such as blocks, it helps to put a film of lubricant on the bearing before cam bearings are pressed in. “Sometimes the bearing can gall and produce an asperity on the inside of the bearing because it is put together dry,” he says. “Surface finish on the cam journals can also be an issue. Some can have rough surface finishes that can fail a bearing.” When installing cam bearings, always work your way from the rear of the block forward. When fitting aluminum cam bearings, it’s important to allow sufficient bearing-to-camshaft clearance, since the harder aluminum alloy bearings won’t wear in as rapidly as babbitt bearings to make their own clearance. Minimum clearance should be 0.002˝ for stock engines and 0.003-0.004˝ for high-performance engines. If cam fit is too tight, bearing material can be removed by reaming. Honing bearings to size is not recommended because honing stone grit can easily be trapped in the bearing surface, and its presence can lead to premature camshaft journal wear. Other variables to consider when replacing cam bearings are things such as casting shifts, which can occur in a cast-iron or cast-aluminum block as the block “seasons” during its initial use. The block can become distorted due to temperature extremes (overheating) and improper installation where excessive or unequal cylinder head fastener tightening had occurred. 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. ■ Circle 24 for more information 24 July 2015 | EngineBuilder

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