Automotive engine reconditioner RPM improves product quality with Flex-Hone
RPM, a Holman Enterprise company and leading manufacturer of automotive parts, has in recent years introduced a metal finishing system that has improved the quality of the inner cylinder surfaces of its remanufactured engines.
The new process includes a special deburring/finishing tool that is used to machine the cylinder wall after a rigid honing operation. Results show that the company’s overhauled engines have fewer engine failures due to inadequate adaptation of the piston rings to poorly machined cylinder walls than those of the competition.
RMP, a Holman Enterprise (Pennsauken, NJ) company, remanufactures car and truck engines and related parts, including master cylinders, water pumps, carburetors and alternators.
As an authorized manufacturer for Ford and Chrysler, RMP distributes its products through three branches on the East Coast, which in turn supply Ford and Chrysler dealers. With over 300 employees, the company has an annual turnover of more than 20 million dollars.
In a typical month, RMP overhauls around 1,300 gasoline-powered engines (70% for trucks, 30% for cars). The warranty for truck engines is 12 months or 12,000 miles; for car engines 6 months or 6,000 miles. RMP used to machine the cylinders of the engines with a standard honing machine, but found that the surface finish did not meet the company’s specifications. The cylinders of the engines range from 6 inches to 7 inches in depth and from 3 inches to 5 inches in diameter.
According to Dale Houghton, head of the engine department at RMP, the cylinder walls of the engines had an unclean finish, with cut, cracked and folded metal remaining along the cylinder surface. This type of finish could ultimately lead to engine failure.
This problem could occur during the running-in period of the newly overhauled engine if the finish interacts adversely with the piston rings. The principle of interacting metals states that the pressure on the surface of the cylinder wall is equal to the load divided by the projected bearing area. For example, if there is a pressure of 500 lb./sq. in. on the bottom surface of two interacting metals and both surfaces are theoretically flat, the pressure on the surface is 500 lb./sq. in.
Since no surface is perfectly smooth, there will inevitably be some abrasion between the surfaces of the cylinder walls and piston rings. If the surface is 80% smooth or flattened, the pressure is 625 lb./sq. in. If the surface is 10% flattened, the pressure rises to 5000 lb./sq. in. which can lead to severe engine damage.
Looking for a solution to its surface finishing problem, RMP turned to Brush Research Manufacturing Co., Inc. (Los Angeles, CA), which provided the company with a new type of deburring/finishing tool known as Flex-Hone®. This system consists of an elastic hone with abrasive fins on the ends of high-density nylon filaments. At RMP, the hone is inserted into a hand-held air tool and secured with a standard key chuck.
The improved honing process at RMP works as follows: Motors come to the company through a dealer exchange program or from core suppliers. The engines are then completely dismantled, cleaned and inspected several times. The engine block is drilled after passing various tests.
Between 0.001 inch and 0.006 inch are removed from the cylinder wall. After drilling, the engine block is machined with a semi-automatic rigid honing machine that removes 0.0001 inch from the cylinders.
The Flex-Hone tool is inserted immediately after this step. To break the remaining metal tips in the cylinder walls, an operator applies three to four strokes of the tool to each cylinder.
The honing tools vary in diameter from 4 1/8 inch to 4 1/2 inch and are provided with 120 grit silicon carbide. RMP uses an average of 280 flex hones per year, or 60 motors per hone. The cost of the units is just a few cents per motor. As a result of using the Flex-Hone tool, RMP was able to maintain high quality standards at minimal cost. According to Houghton, the overhauled engines from RMP have a faster running-in time, better oil retention and reduced blow-by effects due to the plateau finish in the cylinder walls.
RMP is so pleased with the Flex-Hones, says Thomas Carter, the company’s purchasing manager, that they also use them to finish their refurbished master cylinders. For this honing process, the operators use compressed air-driven flex-hone tools from 1 inch to 1 1/2 inches in grain size 180 made of silicon carbide.
