Engine and clutch (stock)/Crankshaft pulley marking

From Motorious

Overview

A crankshaft pulley with various markings on it.

Crankshaft pulleys are marked to indicate the rotational position of the engine. Detailed information about this topic is available on the top dead center (TDC) page. The position of the engine is identified by aligning a known mark on the pulley with the split centerline of the crankcase behind the pulley. These markings are an essential part of engine timing adjustments and valve adjustments.

Original pulleys came from the factory with one or more marks (notches and/or dimples) which indicated the TDC position and others. Most aftermarket pulleys have one or more marks. If you aren't certain what the markings on your pulley represent, you can look them up using this guide.

If the pulley in your car only has a TDC mark, the information below will explain how to make the remaining marks yourself. If your pulley doesn't have any markings at all, buy a new stock VW Beetle pulley as methods for determining TDC with a completely unmarked pulley are inaccurate (with the exception of positive stop).

Preparation

• Before beginning, select a marking method. The mark should not interfere with the operation of the pulley, should be permanent, and needs to be visible when used with a stroboscopic (i.e. bright flashing) timing light. A drop of white paint works well, but other markers are also viable. Discuss marking techniques here.
• Apply the parking brake and put the car in neutral. In this procedure, you will be rotating the engine by hand, so it needs to be disengaged from the transaxle.
• Identify your pulley's TDC mark using this guide.

Step 1: Rotate the engine clockwise until the TDC mark is visible on the top of the pulley.

Using a wrench on the generator/alternator nut to rotate the engine by hand (via the generator/alternator belt). NOTE! Rotate the engine clockwise (the direction it runs). Rotating it backwards (counter-clockwise) introduces play in the various parts and leads to inaccuracy in valve adjustments as well as timing adjustments. If you need to turn the engine backwards, turn it at least 90 degrees back and then advance it to the desired position.

Step 2: Verify pulley diameter and add the markings.

NOTE! Marks made on the right side of TDC correspond to timing angles before TDC because they pass the crankcase split ahead of the TDC mark when the engine is running (clockwise). Marks to the left would be after TDC.

Illustration of TDC and degree markings on the crankshaft pulley.

Use the tape measure to determine the diameter of the pulley (hook the end of the tape on the very bottom of the pulley). If it's 175mm (6 7/8"), then use the values in the table to add markings at 5°, 7.5°, 30° If the pulley is a different size, you can determine the arc distance needed by using this formula:

arc distance = d * π * α / 360

Where:

• arc distance = distance around outside of pulley
• d = pulley diameter
• π = 3.14159
• α = angle

Arc distance and pulley diameter will be in the same units (mm or inches). If you already have markings on the pulley and you want to know the number of degrees between them (this will not tell you which one is TDC), then use this formula:

α = arc distance * 360 / d / π

TIP! For a big angle (like 30°), it's especially important to measure the arc distance along the outside of the pulley (not in a straight line). One way to do this is to carefully measure and cut a piece of tape to the desired length (arc distance) and apply that temporarily to the top edge of the pulley with one end at the TDC mark.

TIP! If you need a flexible ruler, you can actually print one out from this site.

Step 7: Mark the 180° point exactly opposite TDC.

Example of a pulley marked at 180° from TDC. The line in the middle represents the actual 180° mark and the 2 and 4 indicate that this is the mark used when adjusting the valves for cylinders 2 and 4. The 180° mark is not used during timing, but is used when adjusting the valves. You can use a straight edge and a keen eye to find 180°. Just rotate the engine so that the TDC mark is facing downward and line up the straight edge through that mark and the middle of the pulley. TIP! Seeing the TDC mark when it's facing the ground is impossible unless you also make a TDC mark on the front edge or inside lip of the pulley (even a temporary mark is ok).

Cleanup / next steps

With the correct pulley markings, you are now ready to set the timing and/or adjust the valves.

Related links

• Crankshaft pulleys
• Firing order
• Timing adjustment
• Valve adjustment

About this article

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