1. Timing Mark Alignment: The most accurate method involves aligning timing marks on the crankshaft pulley and the camshaft sprockets. These marks are visible when the timing cover is removed (a significant job). The exact specification is found in your vehicle's factory service manual. This manual will specify the correct alignment for both the intake and exhaust camshafts, and it's crucial to follow this precisely. There is no substitute for this.
2. Timing Light: A less precise method involves using a timing light. A timing light will show you the crankshaft's position relative to the timing marks, but you'll still need the factory service manual to determine the correct setting. You'll also likely need to adjust the distributor to set the timing.
Why there's no single number:
* Engine Wear: Over time, engine components wear, and the timing might need slight adjustment to maintain optimal performance.
* Temperature: Timing can be slightly adjusted for different operating temperatures.
* Specific Engine Variations: Even within the VG30E engine family, there could be minor variations affecting the precise timing specifications.
In short: You must obtain a 1990 Nissan G20 van (with the VG30E engine) service manual. It's the only reliable source for the correct timing specifications and procedure. Attempting to adjust the timing without this manual is risky and could seriously damage your engine.
