High Performance Diesel Engines

Bruce Mallinson & Leroy Pershing
June 2023

Vibrations can be the death of your truck and wear out your body 2 hours faster per day.  Torsional Dampers are many times referred to as Harmonic Balancers; that is NOT the correct term, it’s a Torsional Damper.  This damper is a critical part of the engine and eliminates many parts from being broken.  Parts such as crankshafts, camshafts, accessory drive shafts, alternator brackets, air conditioning compressor brackets, the springs in the clutch disc, the flywheel bolts that hold the flywheel to the crankshaft, and the bolts that hold the flywheel housing to the block all will last longer with a working Torsional Damper.  Also, a worn out torsional damper will vibrate the shifter, the door locks, and the steering wheel.  These vibrations can make your hands numb and travel up through the seat into your body and make you tired.  A new torsional damper will give you 2 more hours of energy per day while driving. 

Torsional dampers are worn out at 500,000 miles or less and should be replaced.  The torsional damper has a large steel ring inside the case, it rides on Teflon pads and is cushioned by a very thick silicone that is under 30 psi of pressure.  As the Teflon wears out it impregnates the silicone, the chemical reaction makes the silicone hard, and the large steel ring can no longer move free.  That ring at 1400 RPM moves 700 times per mile to remove the shock when the injector fires and slams the piston to the bottom of the stroke.  

Several years ago we invented a mercury filled engine balancer to compensate for the pistons, connecting rods and crankshaft being slightly out of balance.  We also recommend this balancer to be mounted to the crankshaft along with the new torsional damper.  The Mercury filled balancer is a one-time purchase, it does NOT wear out. 

      Driveshafts are another wear item on the truck and should be rebuilt between 500,000 and 800,000 miles.  Driveshafts do bend and go out of balance, the carrier bearing wears out, and the universal and slip joints wear out.  A good driveshaft shop can straighten, balance and replace the worn components.  This is another item that will vibrate a truck. 

Using a vibration analysis tool, you can determine the vibration's origin based on its frequency. In a previous article, we introduced this topic, and in this article, we will dive more into engine-related vibrations. When you have a vibration that is the same speed as the crankshaft, this is known as a first-order vibration. This can include things like the damper, crankshaft, or clutch assembly. These vibrations can be felt with the truck sitting still and are repeatable at the same RPM. Since the camshaft turns at half the speed of the crankshaft, vibrations will show up on the analyzer as half-order vibrations or half the frequency of the engine speed. Within these frequency ranges, it is easy to tell if you have a faulty injector or cylinder. This can also be quickly done with a cutout test; the vibration analyzer is overkill. High torque vibrations are seen within the four to four-and-a-half-order vibrations. They are found with the use of our dynamometer. Finding these types of vibrations would be easier and safer with the dyno.

I could give more examples of orders of vibrations and their sources, but it is best to sum up this idea with the idea that everything has its own frequency based on its rotating speed. These speeds can be calculated based on what they are attached to or the size of the rotating object. The best example of this is tires. Smaller tires spin faster or have a higher frequency than larger tires. Think skateboard wheels and car tires going at the same speed. The smaller wheels have to turn more quickly. As a side note, one quick tip to calculate your tire revolutions per mile is to place a straight 2x4 on top of both drive tires and measure the distance from the bottom of the 2x4 to the ground. Then on a calculator, type in 20168 / height of drive tires. This will give you your revs per mile. If someone is setting up your ECM, they will ask for this number. Another way this number applies is if you need to calculate your truck's rear axle ratio. You can figure that out with this method. First, put your truck in direct drive and write down the engine rpm and speed. Then take the engine speed and multiply it by 60. Write that number down. Multiply the vehicle speed in mph by the revs per mile of the tire. Write that number down. Finally, divide the first number by the second, and you will have the axle ratio. For example, you have a truck that does 50 mph at 1500 rpm in 11th gear on a 13-speed transmission. First, you take 1500 X 60, and you get 90,000. In this example, the tire revs per mile is 507. Take 496 X 50mph, and you get 24,800. Finally, divide 90,000 / 24,800, and your axle ratio would be 3.55.

Written by: Bruce Mallinson & Leroy Pershing, Pittsburgh Power, Inc., 3600 S. Noah Drive, Saxonburg, PA, 16056

Phone (724) 360-4080 Email: [email protected]