I reported earlier in the week that my engine froze up. Having reviewed my service records, the warranty company ordered an autopsy. I just received word from the Ford dealer that the cause of my engine's death was that the drive gear on the oil pump broke. The next hoop will probably require an inspector from the warranty company to survey the damage. So far, it looks like I will get reimbursed for a rebuilt motor. Stay tuned.
Drive Gear on Oil Pump is Broken
- Thread starter 01mgvert
- Start date
trinity_gt
10 Year Member
trinity_gt
10 Year Member
01mgvert said:
The factory pulley assembly, if you look closely, has a rubber-insulated "inertia ring" bonded to it. As the crank is hit by power stroke impulses from the individual cylinders, it twists slightly. With 8 cylinders firing a few thousand times a minute, there will be alot of torsional vibration.
At certain points in the RPM band, the frequency at which the impulses are imparted to the crank matches the natural frequency of the crankshaft in that mode of vibration which can result in "constructive interference" of torsional waves. This is known as "resonance" and there will be possibly several points in the RPM band where this occurs, at the fundamental crank frequency and at integral "harmonics" of the fundamental.
In a nutshell, the crank can really start to vibrate in torsion at some RPM values. The damper is specifically designed to "dampen" these potentially damaging torsional vibrations by using the rubber-insulated inertia ring to work against the vibrations in the crank. The tuning of this ring and rubber insulator - the mass of the ring, the diameter (i.e. where the mass is located from the axis of rotation), the durometer of the rubber were all the subject of considerable research at Ford.
By putting on aftermarket pulleys, you tossed out the factory damper. While the new unit may have the same mass, it may likely doesn't preserve the diameter of the interia ring and may not preserve the durometer of the insulator. As a result, the damping action is different and may not be ideal anymore.
The damage to the oil pump comes from (a) the fact that the oil pump drive gear slips over the crankshaft snout, sitting just behind the camchain sprockets so it sees crank vibrations directly and (b) the fact that the factory pump gear is a cheesy, powdered metal deal that has little resistance to fatigue. A torsionally vibrating crank snout can pound the gear till it fractures.
