When the Powertrain Division of General Motors began developing a new V6 and V8 engine family, one of the primary goals was to increase engine longevity and reduce warranty claims. The design team approached Chicago Rawhide for its technical expertise on high performance crankshaft seals. The target was to develop a crankshaft seal capable of performing for a minimum of 150,000 leakfree miles.
   

Chicago Rawhide recognized this as an opportunity to transfer some of its heavy duty truck technology to the automotive original equipment market, and accepted the challenge. Typically, a diesel engine crankshaft seal can run hundreds of thousands of miles before replacement. The patented CR Unitized Bonded PTFE seal, with its proven track record in large diesel engines, was downsized to fit GM’s automotive application. Mike Northcott, Chicago Rawhide Application Engineer for automotive engine applications, worked closely with the engineers at GM to tailor the CR design to the new generation V6 and V8 engines. The resultant design is shown in Figure 1. The primary components of the seal are a sleeve, a steel case, a PTFE wafer, and a metal-to-rubber-to-PTFE bond area. Figure 1 illustrates how the PTFE wafer forms both the primary seal lip and the axial dust lip. In test after test, the axial dust lip has proven to be a superior design to the traditional radial dust lip seal.
   

This is due to the fact that the sleeve, which contacts the axial dust lip, acts not only as a barrier to dirt intrusion but also as a slinger that throws contaminants out and away from the sealing surfaces. For comparison purposes, Figure 2 shows a typical PTFE seal design with an industry standard radial dust lip.
   

The rear crankshaft seal, shown in Figure 1, is a straightforward design, based directly on the Chicago Rawhide seal used in diesel engines. The front crankshaft seal, however, required a different approach. A typical unitized seal design requires the seal and sleeve be installed in the engine simultaneously because it is a unitized assembly and can’t be disassembled. Since the front seal shaft surface is on the engine damper, it’s impossible to access the seal cavity with the damper installed. To solve this problem, it was arranged for the damper manufacturer to install the sleeve directly on the damper assembly and ship the modular component to General Motors. The GM engine plant at Livonia, MI, places the seal in the front cover, and then installs the damper and sleeve onto the crankshaft and into the seal. The front seal could now be more accurately described as a semi-unitized assembly.
   

Ordinarily the use of non-unitized, or semi-unitized, PTFE seals poses the risk of damage to the sealing wafer during handling and installation. To assure success for a semi-unitized seal in a high-volume engine assembly environment, CR developed a special plastic protective sleeve that’s installed into the seal by the manufacturer, and remains in place until the engine damper is installed. The sleeve performs several functions, including pre-forming the wafer to the desired diameter, enabling the seals to stack for shipping and automated installation purposes, and protecting the PTFE wafer until the damper is installed. Because the seal is assembled into the front cover of the engine before the protective sleeve is removed, custom installation tools were required at the Livonia Engine Plant.
   

CR was responsible for the design of the installation tools used to install the protective plastic sleeve as well as those required for the crankshaft seals at the Livonia Engine Plant. All of the installation operations are automated, except removal of the plastic protective sleeve, which is done by hand. The plastic sleeve removal tool thus had to be ergonomically designed for ease of use and speedy operation on the engine production line. The process had to be foolproof so inattentive handling wouldn’t damage the seal. The tool and plastic sleeve were developed and tested simultaneously, in order to work together flawlessly.
   

The CR seal design is unique to the industry. Most PTFE seals currently in production depend on clamping force between two steel cases to hold the PTFE wafer(s) in place. This clamped design is commonly known as an “assembled seal” and is shown in Figure 2. When there is high interference between the seal bore and the outer diameter of the seal, the clamped area of an assembled seal can separate, permitting oil leakage around the outer diameter of the wafer (see the area marked “Potential Internal Leak Path” in Figure 2). Separation has caused warranty problems in the diesel engine market. CR solved the leakage problem by bonding the PTFE wafer to a specially developed rubber compound that also bonds to the steel case, eliminating a potential leakage path behind the wafer (see the PTFE-to-Rubber-to-Metal Bond” area in Figure 1).
   

The new design has been tested extensively both at the CR test lab and at GM. The battery of tests include durability, slurry, dust, cold temperature, dynamometer, and road vehicle tests. A new dust test, nicknamed the Puffer Test, was developed by CR for the GM program. The nickname stems from the intermittent bursts of dust that are blown directly at the seal. This application of dust and air accurately simulates real highway operating conditions. During this program, the CR seals performed so well that the Puffer Tests were stopped after 10,000 hours with no failures.
   

Once the design of the seals was finalized, producing the volume of pieces required by General Motors proved a challenge for the CR process engineering department. In order to meet the daily production rates, the development engineers designed a cold runner injection mold specifically for the PTFE seals. In heavy duty/off highway applications, polyacrylate is used as the medium to bond the PTFE wafer to the steel case. Previously, this has been accomplished on hot-runner injection molds, a process which generates a fair amount of scrap. Since the GM applications requires fluoroelastomer instead of polyacrylate, and because fluoroelastomer is significantly more expensive than polyacrylate, it was necessary to minimize scrap. This was achieved with the development of a custom cold-runner molding system.
   

The cold-runner system houses most of the sprues and runners, i.e., the channels in the mold in which the rubber flows to the main cavity or arena of the seal. By maintaining a low temperature in the cold plate, the rubber in the sprues and runners doesn’t cure. This eliminates scrapping after every heat (press cycle) as is the case in a hot runner system. The cold plate is separated from the mold when the press is open, and a plate insulates the cold plate from the mold when they meet during the molding operation. The process allows for very efficient manufacturing in CR’s Springfield, SD, plant.
   

The seals will first see production in the 1999 model year in the GM 3.5 liter DOHC V6 engine produced at the Livonia Engine Plant. The same seal will also be used in the new Northstar engine scheduled for production in model year 2000. The 3.5 liter engine will power the Oldsmobile Intrigue and be available as an option on other vehicles. GM is watching the performance of the Chicago Rawhide seals very closely, since it plans on using PTFE seals in future engine designs.
   

The CR seal for this new GM V6 and V8 engine family illustrates the close supplier/ OEM design development that Chicago Rawhide can provide and is a perfect example of successful technology transfer between different vehicle applications.