Failure Analysis
101
A properly maintained engine will provide years of service. Occasionally an engine will fail. An important part of
working on engines is being able to recognize the root cause of engine failures. Was it something the customer did?
Was it a manufacturing defect? Did the engine just wear out? All of these questions need to be answered. Identifying
and eliminating the cause of the failure is the only way to prevent recurring failures.
Engines can fail in a variety of ways, but most failures can be classified in the following categories:
• Abrasive ingestion
• Insufficient lubrication
• Overspeed
• Overheat
• Mechanical breakage/ wear
NOTE: Keep in mind that the engine may have failed due to a combination of causes.
Each cause of an engine failure leaves its own fingerprint on the engine. Careful gathering of information about
the engine will identify one or more of these fingerprints. Start by getting as much information as possible from the
customer, such as: symptoms, how it is used and the maintenance history.
Abrasive Ingestion
Abrasive Ingestion is when hard particles are intro-
duced into the engine. Particles can be introduced into the
engine by:
• Leaks in the Intake System.
• Through a dirty oil fill plug or dipstick.
• Internal part wear, especially during the break
in cycle.
• Worn or improperly installed seals or gaskets.
1. Common abrasive particles that enter the engine
through the intake system are sand, hay and dirt.
See Figure 11.1.
2. Abrasive particles that enter the engine usually
leave tracking marks where the particles entered
the system. Use these marks to find the source of
the abrasives.
3. Particles that enter the intake system travel at great
speed. These fast moving particles can damage any
parts they contact, resulting in excessive surface
wear.
NOTE: Choke and Throttle Shafts are very vulnera-
ble to this type of wear. If an air filter
becomes clogged, the vacuum produced by
the engine will try to draw air in by any
means possible. This usually happens around the Throttle and Choke Shafts. Because the Throttle
Shaft moves more than the choke, it will wear faster.
4. The particles can pass through the Intake System to the valves and valve seats.
CHAPTER 11: FAILURE ANALYSIS
To Next Page
Loading...
Need help?
General
