While our 1986 Mustang 5.0, Project 666, is supposed to run like hell, there’s no reason for it to shake like it’s possessed. Unfortunately, at idle it was as thrashy as a wet dog, and there was a bit of oil and grease coming from the seal in the timing cover. We didn’t need much more evidence to know we needed to exorcise a worn out harmonic balancer.
The vibration was bad at idle but got worse as the RPM increased. On a test drive around the block, the vibration shook the entire front end as if there was an alignment problem. We just had the front end aligned, so that was ruled out quickly. The next step was to take a closer look at the stock balancer and what we saw was as horrifying as Linda Blair’s head turning 360 degrees.
The elastomer rubber was coming out from between the two sections of the balancer. A couple of hard launches and the outer ring of the balancer would have come off and flew around the engine bay like a pinball. Even if the outer ring didn’t part company, a “spun” balancer isn’t doing its job, which can cause severe engine problems including a cracked or broken crankshaft.
A cure for the shakes….
Harmonic balancers, or vibration dampeners as they are sometimes called, don’t actually balance anything. “Harmonic Balancer” is simply the name of a part, not an accurate definition of what it’s supposed to do. Having said that, we can define the harmonic balancer as ‘a friction-actuated energy-dissipating resonance decelerator.’ While that sounds complicated, what it’s designed to do isn’t all that difficult to understand.
Due to their mechanical design, all internal combustion engines have crankshaft torsional vibration. Pressure varies with the position of the crankshaft in relationship to each firing cylinder. As the piston rises and falls, so does cylinder pressure. This force acting on the piston is transmitted to the connecting rod and applied directly to the crankshaft. As the crankshaft assembly rotates, the forces reverse back and forth as the pressure varies. The crankshaft reacts and transmits these forces as torsional vibration.
The deflection caused by the connecting rods pushing down on the crankshaft journal and the resulting rebound deflection are the primary causes of harmonic vibrations.
The most common type of harmonic balancer has an inner ring that connects directly to the crankshaft snout, an outer inertia ring, and a bonded elastomeric rubber element that connect the rings together. The elastomeric element serves to cushion the torsional forces caused by the acceleration and deceleration of the crankshaft and the rotation of the outer inertia ring.
Over time, the elastomeric rubber element will weaken and separate from the inner and outer rings of the balancer. As the rubber extrudes from between the two balancer rings, the resonance vibration generated by the pistons and crankshaft are accelerated to the point where the entire engine will shake violently. The only solution to this problem is to replace the worn balancer.
Close up view of stock elastomer style balancer. The inner (hub) ring has a direct connection to the crank, while the outer ring is attached through a bonded elastomeric element.
Over time, the elastomer breaks down and starts to squeeze out from between the rings. When it does, the outer ring will often “spin” and change position relative to the hub. In an externally-balanced design like this, where the outer hub has an offset center of gravity, the engine will shake like crazy.
To replace our snakebit stock damper, we called on the experts at TCI Auto. TCI has long been regarded as a powerhouse in automotive and truck transmissions and torque converters, and they’ve expanded their catalog with a line of specialty parts like u-joints, slip yokes, coolers and harmonic balancers.
TCI Harmonic balancers come in two flavors; the elastomeric type dampener and an “energy absorber” type dampener that they call “The Rattler”. The “Rattler” is a mechanical design adopted from the aviation industry. Scott Miller from TCI describes the “Rattler” internal workings as steel rollers that fit loosely into a specific number of holes. By using an exact mathematical relationship in the design process, the rollers will roll forward during compression strokes and roll backward during the power stroke to keep the engine speed variations and vibration to a minimum.
While the “Rattler” Harmonic Balancer is a very trick piece that solves the vibration problem permanently, we were going to be replacing the Stang’s stock engine with a 351W in the near future. We chose to go with TCI’s elastomer harmonic balancer for the rest of this engine’s lifespan in our project car. TCI’s elastomer balancer is built to conform to SFI 18.1 standards and is capable of handling 12,000 rpm. The upgraded TCI elastomer balancer would fit our needs perfectly.
TCI’s elastomer balancer meets SFI standards, meaning that it’s approved for racing use and is far less likely to come apart in an inelegant way at high RPM.
Balancing Act
Mustang V8 engines are externally balanced. Offset weighting on the flywheel and harmonic balancer are used to avoid the need for a lot of extra mass on the internal crankshaft counterweights. Using a harmonic balancer that isn’t weighted correctly for the internal rotating assembly will cause a vicious vibration in the engine. For our stock engine package, we opted for the stock-type 50-ounce balancer.
We started by removing the old, beat-up balancer. Getting to it was easier than it would be on most stock Mustangs because we had already gotten rid of the air conditioning compressor, power steering pump, smog pump, and the engine-driven radiator fan. In place of these we had installed a Meziere electric water pump, a Flex-a-Lite electric cooling fan and a March pulley drive system. These upgrades left a lot of open space so we only needed to remove the serpentine drive belt and the crankshaft pulley.
Once the belt and pulley were removed, the center bolt in the crankshaft was removed. Using a harmonic balancer puller (not a three jawed puller that will simply rip the out inertia ring of the balancer) the old dampener can easily be removed. We found some surface corrosion and caked-on grease on the crankshaft nose. This was removed with acetone and a light coat of machine oil was applied to help protect the machined surfaces.
The new balancer goes on to the crankshaft snout-first, of course. Don’t forget the key when you press it on, and don’t reuse the old one. A new key is cheap compared to the hassle of having to remove and replace a broken one.
Make sure the key is securely installed in the keyway on the crankshaft and install the balancer on the end of the crankshaft. Seat the balancer on the crankshaft by hand. Here’s the key to a successful installation of a long-lasting harmonic balancer: Don’t use a hammer! Beating on the new harmonic balancer is only going to shorten its life, damage the balancer beyond use, or even hurt the crank snout. Using a hammer to seat the balancer is low class. There is a tool made specifically for balancer installation called, appropriately enough, a harmonic balancer installation tool.
The Harmonic Balancer Installation Tool. The name says it all.
Worse than beating on the new balancer with a hammer to seat it is using the center bolt to pull the balancer onto the crankshaft. That’s not low class, that’s simply no class. Using the center bolt runs the risk of damaging the bolt threads in the snout of the crankshaft. Then the real problems begin, like replacing a crankshaft because the threads are pulled out.
Applying grease to the inside of the balancer will help installation on the crankshaft and prevent galling.
Using the right tool to press the balancer onto the snout will protect the crank threads and keep the balancer from jamming due to being slightly off-kilter.
Once the harmonic balancer is seated on the crankshaft, the installation tool can be removed. Ensuring that the large washer is on the center bolt, coat the bolt’s threads with thread lock. Thread lock will prevent the bolt from backing out under the high speed revolutions and high frequency vibrations that the crankshaft will experience.
Using thread lock on the center bolt for security.
No matter what kind of fastener you’re installing, be sure to check whether the torque spec in the manual is “dry” or if it takes into account the presence of thread locker or a lubricant.
In the case of our Mustang, we torqued the center bolt to 121 foot-pounds (the manual called for 93 to 121). In the case of a dynamic rotating component, when given a range of torque values, going with the highest torque value is a prudent choice.
Unless you’ve got a wrist that goes “click” at the right torque value, a properly calibrated torque wrench is a necessary part of your toolkit.
The crankshaft pulley can be reinstalled with the four bolts that hold the pulley to the harmonic balancer. Because the pulley is also a dynamic rotating component subject to vibrations and high revs, the pulley bolts need thread locker and should be torqued to 28 foot-pounds (the manual calls for 20 to 28 foot-pounds). The belts can then be reinstalled and a visual check of the area should be conducted to make sure nothing has been forgotten.
The Moment of Truth
One last splash of holy water (well, it might have actually been windshield washer fluid) and we fired up our Project 666 Mustang after installing the TCI Harmonic Balancer. The shakes were gone, at idle all the way up to redline – maybe there was hope for this project car after all.