The V-belt pulley on all 1986-91 Vanagon water-boxer engines has a sharp, clearly visible notch on the part of the pulley closest to the engine block. This notch is the 5° before top dead center (BTDC) mark. There is another, less visible mark on the pulley on the next peak back (opposite side of that V-belt valley) further away from the block. That is the top dead center (TDC) mark. It is not a notch, but rather an indistinct depression that is about 10mm wide. When using a timing light, timing can be checked by observing the proximity of either of these marks in relation to the parting line of the engine block halves, which is straight up and down, directly in front of the pulley.
VW has two different test procedures for checking ignition timing. One is a rather convoluted method that is part of the "baseline settings," which requires several steps. The whole procedure is to try and verify that a timing of 5 degrees (+/- 3 degrees) BTDC at idle is achieved. The other is a much more straight-forward procedure to check for 35 degrees (+/- 5 degrees) BTDC at 3000 rpm with everything hooked up. The latter is by far the easier and better method for the following two reasons:
1. Verifying correct timing at 3000 rpm is better than checking at idle because timing is very stable at this engine speed and is therefore much easier to verify. The engine management system varies the timing wildly at idle to maintain a smooth idle. This is called "idle stabilization," and it is totally normal. Trying to verify the 5 degree specification at idle requires guesswork, because the reading is just not stable. This is not the case at 3000 rpm verification. Under those conditions, the engine management system relies on a set program to determine timing, and it is smooth and consistent. This will be clearly evident when using a timing light—the mark won't be jumping all over the place.
2. The second reason for checking timing at 3000 rpm is because not only is proper timing being verified, but total advance is also verified. Checking total advance is far more important—not only does proper advance ensure the most efficient and clean running, but also because too much total advance can cause poor performance, dirty exhaust, and even engine damage. Total advance is, in fact, the only critical measure when it comes to timing and, when set properly, idle timing will follow suit.
However (you knew there had to be a "however," right?), the hurdle when checking for 35 degrees at 3000 rpm is that there is no 35 degree mark on the pulley. To complicate matters, the only clearly visible mark on the pulley is a 5 degree BTDC mark. Thus, verifying 35 degrees at 3000 rpm takes some ingenuity. Here are methods that work well:
• Measure the distance between the TDC mark and the 5 degree mark on the pulley. Using this measurement, it is possible to create a new 35 degree mark that is six times further to the right from the 5 degree mark. Once a 35 degree mark is present on the pulley, setting the timing to 35 degrees is a snap with any timing light and a tachometer.
• Using a timing light that has adjustable flash control and tachometer readout, simply dial in 30 degrees and use the 5 degree mark as a reference at 3000 rpm. The resulting setting will be 30 + 5, or 35 degrees at 3000 rpm!