LUBRI CATION Maintenance managers who want to extend the reliability of their vehicles should get to know greases. Th at’s because, too oft en, fl eets overlook proper wheel bearing lubrication, leading to unnecessary repairs and aggravation. In fact, inadequate lubrication is a leading cause of wheel bearing failures in trucks, vans and vehicles of all types. Th e useful life of a roller or ball bearing depends greatly on proper lubrication, which creates a fi lm that separates the bearing’s moving parts, carries away heat and protects surfaces from wear and corrosion. » When packing bearings with grease by hand, technicians should start by placing a golf ball size pile of grease into the palm of one hand. Then, using their other hand, push the large end of the bearing cone assembly into the grease. Photo courtesy of Timken 38 Fleet Maintenance | April 2017 Th is is especially true in wheel bearings where dirt, moisture and high and low temperatures are constant challenges to optimal performance. How Damage Occurs Th e damage caused to bearings by inadequate lubrication can be classifi ed into seven categories: Underfi lling – Grease starvation can cause excessive metal wear. Noise is oft en an early indicator of a problem. Overfi lling – Packing too much grease into bearings can cause problems as well. Excess grease tends to churn inside the bearing, generating more heat. Wrong specifi cation – If the base oil viscosity is too heavy, the bearing’s rolling elements may have diffi culty pushing through the grease and begin to skid. If the viscosity is too light, the thin lubricant fi lm may cause premature wear. Incompatibility – If you use an incompatible grease or substitute, the new mixture may soft en and leak out of the bearing or become lumpy, discolored and hard. Incorrect intervals – Failure to follow maintenance schedules can lead to excessive oxidation in the bearing, causing the lubricant to deteriorate. Deterioration – Grease is a precise combination of additives, oil and thickener. Time and temperature can deplete these properties to the point where the grease is not suitable for use. Contamination – Even small amounts of dirt and debris can disrupt the lubricant fi lm and cause bearing damage. Water is particularly harmful. As little as one percent water in grease can have a signifi cant impact on bearing life. Problem Prevention Th e good news is that it’s easy to avoid most bearing failures. Th e key is for technicians to pay closer attention to lubrication practices. Be sure to share this information with them. To start, if you are unsure about the lubricants you are currently using, work with your bearing supplier to determine the right grease type, grade, amount, additives, supply system and replenishment cycle for the vehicles in your fl eet. Lubricants should be properly engineered for each disc and drum bearing application, based on a combination of factors, including loading, speeds, sealing systems, service conditions and expected life. Particularly where vehicles operate in extreme hot or cold weather, it is prudent to make sure your lubricant is up to the task. Your supplier can also provide recommendations for properly storing grease and maximizing its shelf life. Preparation When servicing bearings, preparation is the key to success. Have your technicians follow these steps to properly pack bearings with grease and avoid problems down the road: By hand: Th oroughly clean hands, or put on new latex gloves. Place grease (golf ball sized) into the palm of one hand. Using your other hand, push the large end of the bearing cone assembly into the grease. Continue pushing grease into the large end, rotating the assembly until grease is forced out evenly around the entire small end. Smear excess grease on the outside of the assembly. Using a mechanical grease packer: Th oroughly clean hands, or put on new latex gloves. Place the bearing cone assembly, small end down, into the grease packer funnel. Plug the bore of the large end of the assembly with the conical retainer. Firmly press down on the conical retainer. Smear excess grease on the outside of the assembly. For best results, a best practice is to allow ample space in the housing. Th is allows excess grease to be thrown from the bearing. Normally, the housing should be one-third to no more than half full of grease during bearing assembly. Once the lubricant has been applied, it is important to monitor it and the bearing for signs of trouble at regular maintenance intervals. Diagnose Damage Bearing damage can vary greatly in appearance, depending on how far the problem has progressed. Always be on the lookout for these warning signs: Darkening of the metal caused by excessive heat – Check for discoloration of the bearing’s races and rollers. In mild cases, this is the result of the lubricant staining the bearing surfaces. In severe cases, the metal itself is discolored. Scoring or peeling – Look for marks cut into the metal or the metal peeling away. Th is can be an indication of a serious lubrication-related problem requiring immediate attention. If a problem is observed, consult a bearing service engineer. In most cases, the bearing will need to be replaced before it can be placed in operation again. With so much to do, busy fl eets can lose track of bearing maintenance. However, a bit more time and attention up front can mean big savings and thousands more service-free miles over the long haul. Don’t Let This Bearing Killer Fleece Your Fleet Proper lubrication prevents many repairs By Dave Novak DIRECTOR, SERVICE ENGINEERING, WARRANTY & LIABILITY, THE TIMKEN COMPANY As a leading authority on tapered roller bearings, Timken (www.timken.com) applies its deep knowledge of metallurgy, tribology and mechanical systems to improve the reliability and efficiency of equipment, machinery and vehicles worldwide. It is also a global leader in bearings and mechanical power transmission products.
FleetMaintenance_April_2017
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