Balance Shaft Sprocket Installation and Alignment Check

Introduction

If a 944 is experiencing vibration problems, the cause could be a balance shaft misalignment. This can occur if the balance shaft belt slips a tooth, the balance shaft belt is broken, or if the balance shaft sprockets are installed incorrectly. Balance shaft sprocket misalignment frequently occurs after water pump, crankshaft oil seal, or balance shaft oil seal replacement.

Other Procedures Needed

• ENG-13: Locating and Setting Engine to Top Dead Center (TDC), Cylinder 1

Installation

Each balance shaft sprocket has two slotted grooves on the inside diameter. One of the grooves on the sprocket will slide onto a woodruff key inserted into a slot near the front end of the balance shaft.

1983–1984 model 944s: Each balance shaft sprocket was stamped on the front with an "O" (Ober/Over) beside one of the slotted grooves and a "U" (Unter/Under) beside the other. On the upper balance shaft, the groove marked "O" is installed onto the woodruff key. On the lower balance shaft, the groove marked "U" is installed onto the woodruff key.

1985 and newer models: Only the groove with the "O" is stamped; the groove which previously had the "U" now has no marking. This is a common source of balance shaft misalignment. Mechanics unfamiliar with 944s may assume the "O" goes on the woodruff key on both shafts — this is incorrect for the lower shaft and causes it to be 180° out of alignment, producing vibration worse than having no balance shafts at all.

Critical: On post-1984 cars, the groove with the "O" goes on the woodruff key on the upper balance shaft, and the groove with no marking goes on the woodruff key on the lower balance shaft.

Checking Balance Shaft Alignment

Proper installation is confirmed visually through the sprocket covers:

1. With the balance shaft sprocket covers installed, it is impossible to see the woodruff key directly.
2. Each balance sprocket cover has a number of round openings and one rectangular opening. At the rectangular opening, there is a tab on the back of the cover which is inserted into the groove that does not have the woodruff key.
3. If the sprocket is properly installed on the upper balance shaft, the "O" stamped on the sprocket will be visible in one of the round openings on the cover.
4. If the sprocket is properly installed on the lower balance shaft, the "O" stamped on the sprocket will be visible in the rectangular opening on the cover.

Note: If the tabs on the back of the sprocket covers are broken off, the only way to positively confirm proper installation is to remove the sprocket retaining bolts, remove the cover plate, and slide a heavy piece of wire or small probe into each groove to locate the woodruff key.

5. Once correct installation is confirmed, verify balance shaft alignment as follows: a. Using ENG-13, set the engine to TDC on cylinder #1. b. With the engine at TDC, the notch on the back lip of the upper sprocket should align with the notch on the rear timing belt cover (approximately 1 o'clock position). c. For the lower balance shaft, the notch on the back lip of the sprocket should align with the raised tab on the inside of the rear timing belt cover (approximately 7 o'clock position). d. Some misalignment is not uncommon — approximately half of all 944s show a slight variance. With one sprocket exactly on its alignment mark, the other should be no more than about 1/2 tooth off. If either shaft is out by a full tooth or more, it must be realigned.