EngineLabs: What are the strongest contributing factors to crankshaft vibration, and which ones are hardest to measure and accurately predict?
Beattie, Jr: Crankshaft harmonics, vibrations or torsionals can all be used interchangeably for the casual talking points. Remember that torsional twist, is a twist without a bend. When you get a twist with a bend, nothing good comes of it. Cranksahft twist is inherent to the rotating assembly in any engine. You will always have pistons on a compression stroke, a power stroke or going up and coming down. This causes the crankshaft to twist. Too much of this twist leads to bearing failure, and eventual crankshaft failure. Many other things are a byproduct of this twist as well. Unchecked crankshaft twist when it does not fail the crankshaft or bearings, will show up in other ways and is often overlooked as being the culprit. A poor performing, or undersized damper that does not properly counteract this twist will allow oil pump failures, timing drive system failures, flexplate or flywheel bolts that come loose, distributor gear failures, and other various gremlins.
Beattie, Jr: The biggest change in elastomer dampers has been the type of materials that can go in them. As rubber develops and companies can use new types of vulcanized rubber to join steel pieces of the damper together, the longer those dampers will last. However the ATI Super Damper became the first damper to utilize two separate sized O-rings on a single inertia mass, and be fully captured inside the shells. An OEM-style damper with two pieces can easily separate, rotate and lose timing marks, or totally fail and come apart. The Super Damper took care of those issues and gave engine builders a package that allowed them to build with lighter engine parts, and turn more rpm, and still keep the torsionals in check.
EngineLabs: In terms of controlling crank vibrations, how much more effective is an internally balanced rotating assembly than an externally balanced assembly?
Beattie, Jr: A well done externally balanced engine will perform just as well as a copy that is internally balanced. However, for higher rpm and fast-revving race engines, internally balanced engines are inherently easier on components and have a better overall life. The reason being is that the mass to counteract the rotating assembly is right where it needs to be. When torsional twist travels on a crankshaft, it runs from the front to the back of the engine, always passing through the middle, mind you. If the mass for the proper balance is there, the better off you are. We have done torsional testing of an internally balanced engine on a circle-track motor that was zero balanced, then 2 percent over and 4 percent over to be sure the torsionals did not change greatly, and the effect was minimal.
EngineLabs: What criteria should engine builders consider when choosing a damper size? What are the pros and cons of larger/smaller dampers?
Beattie, Jr: Size matters. The smaller and lighter the damper, doesn’t make it better. The damper needs to be properly sized for the engines displacement, horsepower, max rpm and the application of the engine. An 864ci motor with a small 5-pound damper might as well not run one at all. And a 305ci motor with a 15-pound damper is not helping itself either. When we spec a Super Damper for a boat, off-road truck or road-race car, we like to use a steel hub on the crank with an aluminum shelled damper assembly. In general, the larger the cubic inch, horsepower and rpm, the larger the damper needs to be to do its job. The correct sized damper will allow the engine to make more horsepower and live longer. Dampers don’t make horsepower, they allow the motor to run how it was designed to run, for the camshaft timing to stay stable, and the engine to live longer. A couple extra pounds on the front of an engine can save a lot of headaches from ever occurring in the first place.
EngineLabs: Engine harmonics is a complicated issue, but what are the talking points that engine builders should know about when selecting parts and setting up the specs to minimize the effects of harmful vibrations and harmonics?
Beattie, Jr: What applications are you building for? Drag racing, road racing, off road, etc. Crankshaft material; cast usually absorbs more low-range torsionals on a torquey low-rpm motor, while a billet crank can live longer and take more sheer horsepower and rpm. Crank weight is important as well. Too light and you will have bearing failures and broken cranks, no matter what damper you run. However, when the crank is heavy for the horsepower and rpm, the damper generally needs to be heavier too with a softer rubber compound to do the job. Some sanctioning bodies like NASCAR do not allow ATI to supply aluminum dampers or parts for safety reasons. Steel dampers are our only choice for the Cup, Nationwide and Truck engines, and other organizations have similar rules. So you better find out before spec’ing a damper. Good main caps are important for torsionals as are the fasteners. If you are constantly getting a burnt bearing, or set of bearings, take a close look. If they are worn from the middle out, and used up almost all the way to the edges, you are doing good. If only the middle, or only the edges are worn, and the other contributing factors are not showing issues, then you have torsional twist going on that a properly sized damper will help.