Sorry guys, I'm so damn busy I don't have much time to hit the boards as much as I used to.
Here is my humble opinion.
For those that don’t know me, my research in engine harmonics goes back to 1994 when I did battle against Fluid Damper on failed cranks, rods and bearings in NASCAR engines.
You can destroy anything by inducing the right harmonic. This can occur if the engine is balanced for a different rpm than which it is operating in. This can also occur as a result of uneven firing pulses. Or perhaps a combination of both and exponentially more cylinder pressure than the crank was ever designed for.
Every engine has naturally occurring harmonics as result of just rotating the engine, now add firing pulses to the mix and the equation just became far more complicated. Induce just the right harmonic or combination of harmonics at the right time, under the right circumstances and bingo we have a broken crank. A “Perfect Storm” scenario.
“Balancing” a crankshaft by attaching weights to the crank to simulate the piston and rod assembly weight, and then spinning it on a machine that senses vibration is nothing more than an attempt to tune these harmonics to occur at an rpm other than where we are going to operate the engine. The crankshaft is never really balanced for all rpms, it is just better in some and worse in others. The key is to make sure the really severe harmonics occur at an rpm in which we won’t be operating. This just targets the rotating assembly and has nothing to do with the harmonics occurring as a result of the firing pulses.
With each firing pulse, energy is transferred through the piston and rod into the crank. Studies have shown that the rod throw on the crank actually deflects and twists, then springs back past it‘s normal orientation, in an ever decreasing fashion until the next firing pulse for that cylinder or the next cylinder attached to that same rod throw, and then the whole nightmare repeats itself. Look up “resonant frequencies” and/or “oscillations” etc. for more in depth explanations. These pulses also send harmonics through the crankshaft.
Greater cylinder pressures can generate greater amounts of twist for a given crankshaft. Increasing the twist past the crankshaft’s limit, results in crankshaft failure. Kind of like bending a piece of metal back and forth until it finally breaks or cracks.
What I find very interesting is the fact that most of the crank failures occur in the same spot. Usually, right behind the first rod throw intersecting the second main journal.
This would indicate an area of concentration for the above described harmonics, whether they are injector related or balance related or both.
We can’t always control these harmonics, as in an injector pulse varying over the life of the injector. The next best thing is to try and absorb and dissipate them, as in the use of a harmonic damper. Dampers can be tuned for specific rpms, power levels, etc using a variety of factors.
Bosch has a specific test procedure for the Dmax injectors. The injector is flow tested at various pressures and pulse widths that simulate real world parameters the injector will see during use. The injector must be within 5% of a target value at each data point in order to past the Bosch test. We typically control our modified injectors to less than 3%, and a very specific spray pattern. Some injectors work great at idle and go away in the mid range, some just the opposite. An uneven firing pulse at any of these levels could be just the thing that burns a piston or breaks a crank. I have tested other modified injectors that were 30% different within the set, the spray patterns were as uneven as the flow would indicate.
The customers never suspected their injectors were that far off from their seat of the pants feel, until the engine failed.
Spinning off the tips and having them extrude honed and reinstalling them without properly flow testing and calibrating is just one giant gamble no matter how you look at it. Some will win, some will lose. It is your engine, your decision. Some shops use air to flow test the tips. Some shops test the entire injector using some test they concocted to fit their test equipment that really isn’t designed for common rail injectors but was instead adapted over. Both result in tests that mean nothing. The injectors need to be tested under the same parameters and pulse widths they will experience in the field, anything less or different is just plain useless info.
Nothing is 100%. The “Perfect Storm” can occur at any time and routinely does in all forms of racing. At best all we can do is take the necessary steps in order to minimize the chance that it will occur.
Guy
