Here's a general overview of the process; however, you should consult a factory service manual specific to your Previa's engine (2AZ-FE or 3VZ-FE) for precise instructions, torque specifications, and diagrams. The manual will detail the specific procedures and precautions for your particular engine. These manuals are often available online or from automotive parts stores.
General Steps (May Vary Depending on Engine):
1. Safety First: Disconnect the negative battery terminal. This prevents accidental shorts and electrical damage.
2. Preparation: Gather the necessary tools, including:
* Factory service manual: Absolutely essential.
* Timing light: Used to verify crankshaft and camshaft timing.
* Sockets and wrenches: Various sizes will be needed.
* Torque wrench: Essential for tightening components to the correct specifications.
* Pulley holding tool: Prevents crankshaft pulley from turning.
* Camshaft alignment tool(s): Often required to properly align the camshafts.
* Possibly a crankshaft position sensor tool: To help you set the crankshaft position.
3. Access: Remove components to access the timing belt and related components (e.g., covers, belts, pulleys, etc.). This often involves removing various auxiliary belts and pulleys.
4. Timing Belt Removal: Carefully remove the old timing belt, noting its orientation and making sure not to damage the components (water pump, tensioner, etc.).
5. Inspection: Inspect all components for wear and tear, including the water pump, tensioner, and idler pulleys. Replace any worn or damaged parts.
6. Timing Mark Alignment: This is the most crucial step. The service manual will detail the exact location of the crankshaft, camshaft, and any other relevant timing marks. Carefully align these marks according to the manual's instructions. This is often done with the engine at top dead center (TDC) on the compression stroke of cylinder #1.
7. Timing Belt Installation: Install the new timing belt, ensuring it's correctly seated in all the pulleys and that the tension is properly adjusted. Use the tensioner and any other alignment tools specified in the manual.
8. Reassembly: Carefully reassemble all the components you removed, tightening everything to the correct torque specifications (refer to your service manual).
9. Verification: Use the timing light to verify that the crankshaft and camshafts are timed correctly. The timing light will show the timing marks flashing at a specific point. If the marks are not aligned, you'll need to re-adjust the timing belt.
10. Reconnect Battery: Reconnect the negative battery terminal.
11. Engine Start and Check: Start the engine and listen for any unusual noises. Check for leaks.
Repeat: Check your engine's timing again after some time (a few hundred miles).
Disclaimer: This is a general outline. Improper timing can lead to catastrophic engine damage. If you are not experienced in this type of repair, take your Previa to a qualified mechanic. The cost of professional repair will be far less than the cost of a damaged engine.
