High-Performance Piston Rings Require "Fool-Proof" Cylinder Honing
“While unquestionably vital to performance, the piston ring is sort of the poor stepchild of the high-performance engine,” says Keith Jones, technical expert at Phoenix-based Total Seal. “They get blamed for just about everything. If there is a compression problem, it’s the piston rings. If there is oil consumption, it’s the rings. I wouldn’t be surprised if the rings got blamed for a flat tire on the way to the race track.”
Jones knows a lot about piston rings and racing. Since 1967 his company has been manufacturing high-performance piston ring sets installed in racing engines used in competition events ranging from IRL (Indy), NASCAR, World of Outlaw sprint car and other racing classes. To stay informed of customer needs and satisfaction, Jones actively solicits feedback from customers, particularly questions concerning performance and critical installation procedures.
Except for its standard automotive line, the countless different ring sets that Total Seal offers are for customized engines, each having many individualized requirements, including cylinder block materials and piston ring designs. Of those, it is particularly important that the piston rings precisely maintain 100 per cent contact with the walls of the block’s cylinder bores. Otherwise, performance problems such as compression blow-by and oil leakage can cause severe, if not catastrophic, problems.
Providing the needed consistent contact between piston rings and cylinder bore almost always requires resurfacing of the bores in racing applications, either because the bores are not perfectly round, have been damaged by previous ring or piston failure, or other wear factors. In any such cases, resurfacing the bores can be a challenge.
“High-performance engine blocks have changed a great deal over the past couple of decades,” Jones says. “One of the most noteworthy changes is the hardness of the block metal, which can be several times harder than it used to be. This has dramatically affected cylinder ring installation requirements because it is now crucial for the customer to achieve proper ring fit inside the cylinder bore at the time of installation.”
Jones explains that in the old days, when engine blocks were composed of relatively soft metals (e.g., 150 Brinell hardness), installers could usually rely on piston rings to adjust to cylinder bores by wearing into the bore surfaces after installation. However, this approach is no longer realistic because today’s engine blocks are much harder (e.g., 330 Brinell), while the high-performance rings are considerably softer with lower tension. The combination simply doesn’t permit that kind of ‘break-in’ technique.
To facilitate proper cylinder bore surface preparation and piston ring-to-bore fit, Jones and other high performance ring manufacturers and distributors recommend the honing of cylinder bores to exacting tolerances (within a few microns). This procedure ensures that excessive compression blow-by and inadequate cylinder bore oil retention are avoided at the outset.
Simplified honing solution
Since bores differ widely according to block hardness, design and engine wear conditions, the proper honing of bore surfaces could become a tricky situation. However, Jones finds that rather than taking a fairly difficult and cumbersome approach of honing with conventional stones, he uses a tool that has cross-hatching capabilities instead. Cross-hatching capabilities are integral to the cylinder bore surfacing requirements of most internal combustion engines, ensuring that proper oil retention will be maintained in the cylinder bore walls at all times.
Using such a tool, parts such as carbide bushings, bore sleeves, hydraulic and pneumatic cylinders, and other cylindrical cavities can be surface finished on the production line or resurfaced in the field with little set-up time.
“We recommend this type of hone because it works very well, is easy to use with a hand-held drill motor, and is really fool-proof for the average consumer that is not an experienced machinist,” explains Jones.
Ed Sullivan is a Hermosa Beach, CA-based writer.
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