How To Install a Torsional Damper Correctly
If a torsional damper is designed to control harmful crankshaft vibrations, then it goes without saying that the damper must be properly installed or it will cause additional vibrations that can’t be controlled.
The damper must fit tightly on the crankshaft snout. Some engine builders have struggled with properly installing a damper and used a brake-cylinder hone or some other stone to open up the inside diameter of the damper beyond the recommended clearances. In fact, some early engine-building books even suggested honing to open up the interference fit.
Lately, however, damper manufacturers have posted suggested clearances than can be easily confirmed through basic measurements with typical micrometers and dial-bore gauges. If the clearances are too loose, it won’t take long for the crankshaft vibrations to enlarge hub opening, possibly damage the crankshaft key or lead to galling of the crankshaft.
Dampers are designed to be pressed into position on the crankshaft before being secured with a bolt and washer. Some amateur builders will try to cut corners and not use a dedicated installation tool, but rather try to press damper on using the crank bolt.
“With a dedicated tool, you’re using the full length and strength of the crankshaft threads,” explains Fluidampr engineer Aaron Neyman. “If you’re trying to install with just a crank bolt, you don’t have as much strength. You could rip the threads right out of the end of the crankshaft.”
Fluidampr includes a detailed set of instructions with all its products. This demonstration shows the installation of an internally balanced Fluidampr damper on a big-block Chevy. The installer used an installation tool typically offered by damper manufacturers and engine-supply shops. This particular tool came from Precision Performance Products, but other similar tools use the same procedure.
A Fluidampr damper uses viscous technology to counter crankshaft vibrations. There are three basic parts to a Fluidampr damper: A CNC-machined housing and an inertia ring are separated by a layer of silicone. The idea is simple: the damper housing rotates at crankshaft speed. When there’s an extreme vibration, the shock moves into the housing and through a layer of silicon before reaching an internal inertia ring. This ring then absorbs the unwanted energy and actually slows down, compared to the engine rpm and the damper housing. As the inertia ring reacts and catches up with the engine rpm, it shears forward through the silicone layer. This free floating motion transfers torsional vibration energy into heat, which radiates through the housing. Fluidampr uses silicone instead of rubber because it dissipates heat better and doesn’t crack or separate with age.
The need for a damper on a street or performance engine is not disputed. Without a damper, harmful crankshaft torsional vibrations can lead to damage in the rotating assembly, disrupt valve timing and even affect the transmission operation. A damper is a simple yet effective way to counteract and control crankshaft vibrations. As a performance tool, it does not add horsepower. It will, however, calm the valvetrain so the engine can realize its full potential. And if the ignition is tied directly to the camshaft or crankshaft, then spark timing is also more accurate.
The wrong damper can also have devastating consequences. So, before installing a new damper, the correct application must be determined. While there are different types of dampers on the market — such as viscous, rubber elastomer or centrifugal pendulum technology — they all are separated into two groups, according to the type of engine balance.
“When you change something, you’re altering the natural frequencies of the engine,” says Neyman. “The rubber damper that comes with the engine works for a small frequency range, usually around 50 Hz. Depending on what you do to the engine, you could be shifting the resonance a lot more than 50 Hz. Buying a quality damper is like buying an insurance policy. It also frees up power. You can lose a lot of power if vibrations are transmitted up through the valvetrain.”
A neutral damper matches up with an engine that is internally balanced — that is, the crankshaft, rods and pistons are balanced as a unit. That means the damper and flywheel/flexplate are neutrally balanced to match. For an externally balanced engine, counterweights are placed on the damper and flywheel/flexplate to compensate for a rotating assembly that is not perfectly balanced.
“If you picked up a motor you don’t know the history on, you want to get a good idea of the crankshaft stroke,” suggests Neyman. “Large-stroke crankshafts tend to be externally balanced. Check everything that’s mounted to the crank for any type of counterweight.”
If replacing a damper on a stock engine with an aftermarket unit, then it’s a simple matter of looking up the correct year, manufacturer and size of engine. However, if the engine has been modified or built from scratch, then more details and consultation with the damper manufacturer are required.
In preparing for installation, engine builders should visually inspect the damper and confirm the part number is correct for the application. Also, if any spacers are required for a specific installation, make sure they’re on hand and also the right size.
The key to any damper installation is keeping the hammer in the toolbox. There’s often an irresistible urge to tap a damper in a circular pattern to force it over the crankshaft snout. Not a good idea as the damper can be damaged.
“This could put a dent in the damper,” says Neyman. “With a Fluidampr damper, we have fairly tight tolerances in the shear gaps where the fluid is located. If you change that gap by putting a dent in the case, it can cause localized hot spots or you could even lock the inertia mass.”
Some amateurs may try to protect the damper with a block of wood while still trying to tap with a hammer.
“That really never goes as planned,” quips Neyman. “Eventually you’ll end up hitting something else.”
Fluidampr recommends removing any nicks or scratches on the crankshaft snout and softening any sharp corners on the keyway. The key should fit snuggly in the keyway but a heavy press fit can create high stress on the slot. If a hammer is needed to drive the key into place, then likely the key is too wide and should be replaced if its condition is questionable.
Use the right tool
A dedicated installation tool slowly and cleanly drives the damper into place once it’s properly positioned over the key. The tool is basically a large threaded screw with some type of disc that keeps the damper square to the crankshaft as it’s moved into place behind the force of a threaded nut. Some engine builders have been known to heat the damper hub with a heat gun or torch. The heat expands the hub slightly for a slightly but temporary loose fit. This is a practice best left to seasoned engine builders, but if the correct tool and procedures are used, then it shouldn’t be necessary to artificially expand the hub for installation. Most dedicated installation tools can also be used to safely remove a damper, as well.
Once the damper is installed, the timing marks must be checked by bringing the #1 piston to TDC on the compression stroke. This is generally done before the heads are installed during an engine assembly. If the engine is installed, then a positive stop should be used in the spark-plug hole. Once the timing marks are confirmed, then pulleys and other accessories can be installed. It’s also a good idea to secure the damper with a new crank bolt, such as the ARP bolt used in this demonstration.
Final inspection will include checking belt alignment when the pulleys are installed