This month's edition of Hot Rod magazine contains an exhaustive article on the subject of the rise in cam failures. The article concludes that the cam blanks themselves are not the problem, but failures are a combination of changes in lifter production sources and oil specs.
The article identifies that only GM continues to make flat lifters; all other OEMs make only roller lifters. Other than GM, there is only one other U.S. manufacturer of flat lifters and that company sold production rights to another company, which shut down the production for about a year. Consequently, production went to offshore suppliers which made cheap and poor quality lifters. Comp Cams and Crane state that they did not purchase from offshore sources and continue to use U.S. lifters, now that U.S. production has resumed. The less expansive engine rebuild kits may continue to use the inferior offshore lifters, which are prone to failure.
Second, for environmental reasons the zinc and phosphorus previously contained in motor oil for gas engines (at least the OEM-spec oil) is largely removed. These are the components that protect cam lobes, the phosphorus in particular. This subjects the lobes to as much as 200,000 psi, which wipes the lobe. The article describes the Shell Diesel rotunda oil, racing oils, and certain engine break-in additive (by GM part numbers) that add back in the phosphorus and zinc, and in some cases, also a friction modifier. The diesel oil contains a potent detergent which cleans the rings. This fine for newer engines, but with a lot of miles, the cleaner rings could result in blow-by.
Finally, there are changes in engine rebuilding that promote early cam failure. Windage trays keep down the splashing as the crank rotates, which cuts back on lubrication to the lifters. Also, with more radical cam grinds (lift), spring rates are higher, which subjects the cam lobes to more wear. Also, the diameter of the lifter bore is critical to the rotation of the lifter as it rides on the cam. When the bore is worn more than a few thousands above the diameter of the lifter, this rotation is not as efficient. To compensate, on a high mileage block, the lifter bores should be sleeved and drilled out to the proper bore spec. Most folks simply run a brake hone down the lifter bore to remove varnish and never mike the bore to see if it is within spec.
To compensate for the reduced oiling from crank splashing, a shallow groove can be cut in the lifter. Comp Cams makes a tool to do this. Some lifters are manufactured with a hole drilled in them for increased oiling.
What is fascinating about this article is learning that all cam blanks made in the U.S. are made by either one of the two companies making cam blanks domestically. Similarly, flat tappet lifters are limited to GM or one other production source. The cam blanks are produced, heat treated, then sent to Crane, Comp Cams, etc, who then put on the lobes. The article provides the names of these companies, which I have forgotten.
The article recommends using the rotunda oil, racing oil if money is not an issue, or regular oil with the break-in additives, one quart of the latter per oil change, at all times with flat tappet cams.
The article identifies that only GM continues to make flat lifters; all other OEMs make only roller lifters. Other than GM, there is only one other U.S. manufacturer of flat lifters and that company sold production rights to another company, which shut down the production for about a year. Consequently, production went to offshore suppliers which made cheap and poor quality lifters. Comp Cams and Crane state that they did not purchase from offshore sources and continue to use U.S. lifters, now that U.S. production has resumed. The less expansive engine rebuild kits may continue to use the inferior offshore lifters, which are prone to failure.
Second, for environmental reasons the zinc and phosphorus previously contained in motor oil for gas engines (at least the OEM-spec oil) is largely removed. These are the components that protect cam lobes, the phosphorus in particular. This subjects the lobes to as much as 200,000 psi, which wipes the lobe. The article describes the Shell Diesel rotunda oil, racing oils, and certain engine break-in additive (by GM part numbers) that add back in the phosphorus and zinc, and in some cases, also a friction modifier. The diesel oil contains a potent detergent which cleans the rings. This fine for newer engines, but with a lot of miles, the cleaner rings could result in blow-by.
Finally, there are changes in engine rebuilding that promote early cam failure. Windage trays keep down the splashing as the crank rotates, which cuts back on lubrication to the lifters. Also, with more radical cam grinds (lift), spring rates are higher, which subjects the cam lobes to more wear. Also, the diameter of the lifter bore is critical to the rotation of the lifter as it rides on the cam. When the bore is worn more than a few thousands above the diameter of the lifter, this rotation is not as efficient. To compensate, on a high mileage block, the lifter bores should be sleeved and drilled out to the proper bore spec. Most folks simply run a brake hone down the lifter bore to remove varnish and never mike the bore to see if it is within spec.
To compensate for the reduced oiling from crank splashing, a shallow groove can be cut in the lifter. Comp Cams makes a tool to do this. Some lifters are manufactured with a hole drilled in them for increased oiling.
What is fascinating about this article is learning that all cam blanks made in the U.S. are made by either one of the two companies making cam blanks domestically. Similarly, flat tappet lifters are limited to GM or one other production source. The cam blanks are produced, heat treated, then sent to Crane, Comp Cams, etc, who then put on the lobes. The article provides the names of these companies, which I have forgotten.
The article recommends using the rotunda oil, racing oil if money is not an issue, or regular oil with the break-in additives, one quart of the latter per oil change, at all times with flat tappet cams.
