March - April 1997 Lane Racing And Rodding Article By Jim Kaekel, Jr.
No, "torsional vibrations" was not the Beach Boys' hit that rocketed to the top of the Billboard charts in the 60's, but it is a condition that exists in most every internal combustion engine's crankshaft. These conditions are more prevalent in racing engines, particularly those that operate at extremely high rpm's for extended periods, such as long track endurance engines.
These "harmonic vibrations" as they are also known, are caused by the forces of combustion. As the cylinders ignite, these forces attempt to hammer each piston and connecting rod assembly into the crankshaft. These harsh conditions cause internal vibrations which eventually transfer to the front and rear of the crankshaft. Vibrations destined to the rear of the crankshaft are transferred to the flywheel and fed thru the drivetrain while frontal vibrations are transferred to the balancer.
Traditional factory OEM balancers are constructed of a steel crank hub and outer inertia ring bonded together by a rubber elastomer designed to dampen vibration. One common problem with OEM balancers is the outer ring turning on the elastomer. When this occurs, naturally the timing mark becomes incorrect. I'm sure there are several racers who have thrashed on their cars for hours, trying to locate a timing problem (myself included), only to discover that the balancer has spun and they're actually running 28 degrees of timing of the 38 degrees they had intended.
It is always a good idea to check the balancer after freshening up your engine. Once the balancer has been installed on the engine, screw a piston stop into the spark plug hole (Tavia #08065 for 14 mm threads and #08068 for 18mm) if the heads are on. If all you have is a short block, secure a piston stop (Tavia #08060) across the deck. Rotate the engine clockwise until the piston comes up against the stop. Scribe a mark on the balancer even with the TDC mark on the timing tab. Proceed by then rotating the engine counter-clockwise until it again comes to a halt. Scribe another mark even with the TDC mark on the timing tab again. Your true top dead center is then easily found by simply measuring half way between the two scribe marks. The half way point should be at or very close to the TDC mark of the balancer. If not, the balancer should be discarded and a suitable replacement found.
An important factor in balancer care is proper installation and removal procedure. More often than not, many a balancer has been installed or removed by beating it with a hammer. A damper installation tool (Tavia #08-200 for Chevys, #08205 for Fords) should be used and a properly designed puller should be used for removal. Be sure that when installing any balancer that it must be pressed onto the snout during installation. If it rattles around on the keyway, it cannot perform properly and should then be replaced.
SFI approval is an important feature when purchasing a new balancer. All NHRA classes with the exception of Stock Eliminator have a mandate on the usage of SFI-approved units. Any bracket car that runs 10.99 or quicker is also required to be so equipped. The circle track sanctioning bodies of ASA, ARCA, Busch, and Winston Cup also require the SFI sticker.
There are several types of aftermarket balancers available if you are in the market for a replacement of your current used and abused part. Balancers such as those available from ATI, BHJ, Fluidampr and TCI are designed and engineered for true race engines unlike OEM units. Most of these aftermarket balancers are also SFI approved.
ATI's Super Damper is a four piece elastomer type available in either steel or aluminum. The ATI part uses elastomer inserts similar to OEM design,. However, the Super Damper uses eight elastomer inserts rather than one, is fully computer machined, rebuildable and is SFI approved.
Also quite popular and reputable is the Fluidampr balancer. Fluidampr's product is of three piece design filled with a slight amount of silicone fluid used to dampen vibration. Like the ATI Super Damper, Fluidampr has been around quite awhile and is also SFI approved.
BHJ, a company that should be familiar to engine machine shops, makes available standard replacement and high quality racing SFI-approved balancers.
Relatively new to the balancer market is TCI. They introduced the "Rattler" just over a year ago. The SFI -approved "Rattler" uses a series of "weights" which move thru centrifugal force to dampen crankshaft vibration.
Be sure to do a little research when in the market for a balancer to determine which one would be best suited for your particular application. You should also determine if the engine is either internally or eternally balanced. Externally balanced engines are identified by a counterweight located on both the balancer and the flywheel.