By Barry O’Leary
Technical Support Specialist
Caterpillar Forest Products
When a machine fails, the result is downtime and repair costs. Making a repair, without analyzing the cause, can result in further costs. Avoid this by following eight steps to gather the facts, determine a sequence of events and then identify and correct the root cause.
- State problem—The problem should be stated in a clear, concise manner in two parts: the failed components and symptoms.
Symptoms observed in the component may include fractures, unusual wear or deformation. Note other symptoms that may be related, such as unusual noise or odor, vibration or loss of power.
Take care not to state the problem too broadly or too narrowly. Here’s an example of what can happen with a too narrow approach: An operator detected low power, black exhaust smoke and no turbocharger “whistle.” He concluded the turbo was bad and replaced it, but the symptoms persisted. The problem turned out to be a bird’s nest in the air inlet pipe.
- Organize fact gathering—An organized analysis will include a list of conditions that could have led to the observed symptoms and failure. Don’t let preconceptions mislead you. If engine bearings get hot and seize, it is reasonable to suspect low oil. However, the problem could be a failed oil pump, for example. Basic equipment for fact-finding should include a flashlight, camera, magnifying glass and filter cutter.
- Collect, record facts—Accuracy in fact collection is critical. You can collect facts at the work site and by saving damaged parts. Service records and a download of the electronic control module are also useful. Results from an oil sample analysis may give important metallurgical and other clues. Write facts down and take pictures if appropriate. Don’t rely on your memory.
- Think logically—Even if you weren’t there, logical interpretation of the facts can give you a good idea of what occurred during the failure.
Events are actions in the machine. For example, a damaged hydraulic cylinder rod is a fact. The corresponding event would be that something damaged the rod. Identifying events that occurred during a failure may point toward a cause. However, be careful not to mistake this step for determining the root cause of a failure.
- Identify root cause—To search out the root cause of an equipment breakdown, create a time line. The line extends from Good to Failed—from the time when everything was operating properly to the time of the problem statement. Between these two times certain events occurred, accompanied by certain facts, such as heat, smoke or unusual noise. Put the events in chronological order. The facts of one event may “overlap” with the next event. When the events are all correctly placed on the time line, you will be able to see each event leading to, or causing, the next. It’s like an accident investigation. When you examine the first event on your time line, ask whether it is actually a result. If so, make a list of events that could have been the cause. For example, if the machine is a loader and your timeline included “damaged hydraulic cylinder rod,” causes might include: hitting a bunk stake on a log truck or damage from a chain during transport. Look for facts to confirm which of the possible causing events actually occurred. Repeat this process until you have identified the first abnormal event, and the root cause of the breakdown.
- Make repairs—Findings from your time line analysis may suggest a choice of repair options. Generally, the lowest-cost option that addresses the root cause and keeps problems from recurring is best.
- Communicate—Findings should be reported to the party responsible for the failure. This person is usually in the best position to take corrective action and prevent future failures. Other corrective action may include changes in training, procedures or work processes.
- Follow-up—Allow a reasonable period after repairs are complete and normal operations have resumed to follow-up and ensure the corrective action actually fixed the problem. You’ll benefit in the long run when you follow these steps to find the root cause of equipment failure. By eliminating unnecessary downtime and costs, you’ll make your business more productive and profitable.