Engine - Automatic Valve Lash Adjuster Noise
91mitsubishi07
NO. TSB-91-11-009
DATE May, 1991
MODEL All models with Automatic Valve Lash Adjusters
SUBJECT: EXCESSIVE NOISE FROM AUTOMATIC VALVE LASH ADJUSTERS
PURPOSE
This Technical Service Bulletin (TSB) describes a possible cause of excessive automatic valve lash adjuster noise and provides a corrective procedure.
AFFECTED VEHICLES
All vehicles equipped with automatic valve lash adjusters.
Figure 1. Automatic Valve Lash Adjuster (cut-away view):
DESCRIPTION
The most likely cause of excessive automatic lash adjuster noise is the presence of air in the high pressure chamber. (Refer to Figure 1).
Before replacing any of the automatic lash adjusters on a vehicle with excessive valve noise, perform the following procedure. This procedure will bleed unwanted air out of the adjusters and provide positive evidence that there is no need for replacement.
Note: Some customers may comment on a slight valve tapping noise heard upon initial vehicle start-up (especially if the vehicle has not been operated for more than one week). This noise disappears after normal engine temperature is reached. It is important to let the customer know that this is a normal condition and not a cause for concern.
PROCEDURE
1. Check the oil level in the crankcase. If the oil does not require changing, top it off to the full mark on the dipstick. If the oil requires changing, replace the oil and, when required by the maintenance schedule, the oil filter.
2. Start the engine, check for oil leaks, and warm the vehicle up to normal operating temperature.
3. If the valve noise is still present after engine warm up, air may be trapped in one or more of the automatic lash adjusters. To bleed out the air, perform the following steps:
a. Gradually increase engine speed from idle to 3,000 rpm during a 30-second interval. Then, decrease engine speed for another 30-second interval until it returns to idle.
b. This procedure can be repeated up to (but not more than) 10 additional times. After each increase/decrease cycle of engine speed, allow the engine to idle and check to hear if the noise has stopped.
4. If the valve noise still exists, disassemble and inspect the automatic lash adjusters according to the following steps:
Caution: To protect yourself from hot engine components, wear protective gloves and use clean shop rags as needed.
5. Stop the engine and remove the valve cover.
Figure 2. Checking the Operation of the Automatic Lash Adjuster.:
6. Using firm pressure from your finger, push down on the rocker arm over the head of each lash adjuster. Be sure that the camshaft lobe is on the flat side when performing this step. (Refer to Figure 2).
7. If the head of the adjuster sinks when finger pressure is applied, the adjuster must be replaced.
8. If the head of the adjuster stays firm when finger pressure is applied, the adjuster is functioning normally and should not need replacement. At this point, perform further engine diagnostic procedures to determine the origin of the noise. Consult the appropriate section of the vehicle's Service Manual.
WARRANTY INFORMATION
Standard warranty procedures apply