[1] Powerbond produces several...
[1] Powerbond produces several excellent and affordable harmonic dampers that are direct replacements for the common ’68-later Pontiac unit. Butler Performance sells the stock replacement (PN PBO-PB1056N), which Powerbond suggests for applications up to 400 for $75. PN PBO-PB1056ST (shown here) is ideal for high- performance applications up to 600 hp, and sells for $90. We chose it when seeking to replace our Firebird’s original.
The harmonic damper located on the front of the crankshaft serves a very important purpose. It’s designed to absorb the resonate harmonics that can otherwise lead to crankshaft failure. It’s assembled in such a way that any unpredicted imbalance within the unit can cause engine damage or failure, and those symptoms leading up to that can unknowingly occur with age.
Rather than being reactive when any issues arise, we chose to be proactive, replacing our ’72 Firebird’s original damper with a high-performance stock replacement from Butler Performance, repairing a pesky oil leak in the process. Follow along as we explore the steps involved with installing a new harmonic damper, and have our Firebird back on the road in less than two hours.
[2] Powerbond balancers come with a quality black finish. If original appearance is important to you, however, it can easily be painted in a shade of blue that matches your engine.
[3] Disassembly begins by...
[3] Disassembly begins by loosening the accessories with the appropriate wrenches and sockets, and removing their drive belts. The fan and water pump pulley follows, which requires a 1⁄2-inch socket.
A crankshaft flexes and twists with each rotation during normal operation. That action creates a torsional vibration, which can eventually cause the crank to fatigue and fail. A large hub fastened to the front crankshaft absorbs harmonic irregularities to prevent crank failure.
Pontiac used a multi-piece damper that bolted together through ’67. A new unitized design was introduced for ’68, and it’s likely the most common Pontiac damper found today. It measures 63⁄8 inches in diameter and has an outer ring (or inertia weight) that floats about the hub. The two pieces are isolated by elastomer (rubber), which absorbs the torsional irregularities mentioned previously. It’s keyed to the crankshaft for positive location and is fastened by a large bolt.
The ’68-up Pontiac damper is an excellent design with a history of performing very well in stock applications, and even some mildly modified examples producing 400 hp or more. New dampers were available through Pontiac parts departments until a few years ago. Used units are at least 30 years old, however, and the rubber isolator can deteriorate and/or shrink, allowing the outer ring to rotate. That not only affects spark-timing accuracy, it can affect the damper’s balance, negatively impacting its ability to dampen harmonics.
[4] Using a 1⁄2-inch socket,...
[4] Using a 1⁄2-inch socket, the lower pulley (or pulleys if your Pontiac is equipped with A/C) is removed next.
For many other makes, the hub contains a slight imbalance that is used to finely balance the entire reciprocating assembly, hence the name harmonic balancer. That isn’t always the case with the Pontiac V-8, however. Besides original 265/301 units, Pontiac hubs were neutral balanced, serving no balancing purpose. Vintage Pontiac literature refers to it as a harmonic damper, and for the sake of accuracy in this article, we’ll refer to it as such. Be sure the aftermarket damper you’re considering for your Pontiac is internally balanced unless your engine has been rebuilt and is balanced untraditionally.
[5] The damper bolt is extremely...
[5] The damper bolt is extremely tight and any attempt at removing it will cause the engine to turn over. There are myriad methods for breaking the bolt loose, but securely clamping a pair of locking pliers on the ring gear is the easiest. Simply rotating the engine binds the pliers with the bellhousing, preventing further rotation.
A front-crankshaft-seal leak had been little more than a minor annoyance for a few years. It’s a simple repair that we put off for several months, and it happens to require removing the harmonic damper.
Now, the original damper on our ’72 Firebird is more than 40 years old, but it has presented no operational issues thus far, and looked to be in excellent shape. Past experience tells us that there’s oftentimes no telling when or if the outer ring could slip, eventually causing it to fail, and having the damper off to replace the front seal presented us with the ideal opportunity to install a better one.
[6] With the engine bound,...
[6] With the engine bound, the damper bolt is removed using a 15⁄16-inch socket and long breaker bar. Expect to exert a significant amount of force to break it loose. It’s also wise to clean the bolt area with brake cleaner or solvent to remove any grease that’s built up over the years. Be sure the socket is securely seated on the nut during removal. You don’t want to round off the corners!
[7] Pontiac introduced its...
[7] Pontiac introduced its unitized harmonic damper in ’68. While available through GM Parts departments for a number of years, those originally installed on engines are now generally 30-40 years old. A combination of age and engine heat has a tendency to dry up and shrink the rubber isolator, compromising the damper’s functionality. Even though this unit looks to be in good shape, a close look at the rubber isolator reveals otherwise. It needs to be replaced.
[8] A lip-type seal pressed...
[8] A lip-type seal pressed into the timing cover that surrounds the damper hub prevents oil from leaking outward. The rubber is also susceptible to heat and age, and can tear with age creating an oil leak. It’s an excellent idea to replace the seal if it’s original to the car or its age is unknown. We found this Timken unit (PN 332062) for $12 at a local auto parts store.