Balance Shaft Sprocket Installation and Alignment Check – 2.5L NA

Overview

This procedure outlines how to install the balance shaft sprockets and check their alignment on a Porsche 944 with an 8-valve engine. Proper alignment is critical to prevent vibrations caused by a misaligned or slipped balance shaft belt, a broken belt, or incorrectly installed sprockets. This guide is tailored for the 1983–1985.5 (Pre-85.5) and 1985.5–1988 (85.5 Onwards) variants, addressing differences in sprocket markings. Follow these steps carefully to ensure smooth engine operation.

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Tools Required

• 10mm (3/8 inch) wrench
• 13mm (1/2 inch) socket and ratchet
• Small probe or heavy wire (for checking woodruff key location)
• Flashlight (for visibility)
• Torque wrench (capable of 20 Nm / 15 ft-lbs)

Parts Required

• Balance shaft sprocket (upper), 944 102 219 02
• Balance shaft sprocket (lower), 944 102 219 02
• Woodruff key (if replacement needed), 944 102 239 00
• Balance shaft belt, 944 102 219 04

Required Additional Procedures

Steps in these procedures are required to complete this process:

• Locating and Setting Engine to Top Dead Center (TDC), Cylinder 1

Step-by-Step Procedure

Step 1: Prepare the Engine

1. Follow this link to ensure this step – Locating and Setting Engine to Top Dead Center (TDC), Cylinder 1 – of the process is followed accurately to set the engine to TDC on cylinder #1.
2. Remove the balance shaft belt by loosening the tensioner and sliding the belt off the sprockets. Store the belt safely to prevent damage.

Step 2: Install the Upper Balance Shaft Sprocket

3. Locate the woodruff key slot on the upper balance shaft near the front end.

For Pre-85.5 models: Identify the slotted groove on the sprocket stamped with “O” (Ober or Over). Slide this groove onto the woodruff key on the upper balance shaft.

For 85.5 Onwards models: Identify the slotted groove on the sprocket stamped with “O”. Slide this groove onto the woodruff key on the upper balance shaft.

4. Secure the sprocket with the retaining bolt and tighten to 20 Nm (15 ft-lbs) using a torque wrench.

Step 3: Install the Lower Balance Shaft Sprocket

5. Locate the woodruff key slot on the lower balance shaft near the front end.

For Pre-85.5 models: Identify the slotted groove on the sprocket stamped with “U” (Unter or Under). Slide this groove onto the woodruff key on the lower balance shaft.

For 85.5 Onwards models: Identify the slotted groove on the sprocket without the “O” stamp. Slide this groove onto the woodruff key on the lower balance shaft.

6. Secure the sprocket with the retaining bolt and tighten to 20 Nm (15 ft-lbs) using a torque wrench.

Step 4: Install the Balance Shaft Belt

7. Reinstall the balance shaft belt, ensuring it is properly seated on both sprockets.
8. Adjust the tensioner to achieve proper belt tension, following the manufacturer’s specifications.

Step 5: Check Sprocket Installation

9. Install the balance shaft sprocket covers, ensuring the tab on the back of each cover inserts into the groove without the woodruff key.

For the upper balance shaft: Check that the “O” stamp on the sprocket is visible through one of the round openings on the cover.

For the lower balance shaft: Check that the “O” stamp on the sprocket is visible through the rectangular opening on the cover.

Note: If the tabs on the sprocket covers are broken, remove the sprocket retaining bolts, remove the cover plate, and slide a small probe or heavy wire into each groove to locate the woodruff key. Adjust the sprocket installation if necessary.

Step 6: Verify Balance Shaft Alignment

10. Confirm the engine is still at TDC on cylinder #1, as set in Step 1.

For the upper balance shaft: Check that the notch on the back lip of the sprocket aligns with the notch on the rear timing belt cover (approximately 1 o’clock position).

For the lower balance shaft: Check that the notch on the back lip of the sprocket aligns with the raised tab on the inside of the back timing belt cover (approximately 7 o’clock position).

11. If the notches are misaligned by more than half a tooth, remove the balance shaft belt and adjust the sprocket positions to achieve proper alignment.

Post Procedure Checklist

• Verify that the balance shaft belt is properly tensioned and seated on both sprockets.
• Confirm that the “O” stamp is visible in the correct opening on each sprocket cover (round for upper, rectangular for lower).
• Ensure the engine runs smoothly without unusual vibrations after starting.
• Double-check that all bolts are torqued to 20 Nm (15 ft-lbs).

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• YouTube