The term "pattern failure" literally means a failure along a pattern, which is a similar and repeatable failure both in time and nature. Many of the
typical auto parts failures discussed in car-care articles are of a design-specific nature; that is, certain part designs tend to fail along a pattern,
irrespective of vehicle make and model.
Pattern failure explained
All air filters, regardless of vehicle make and model, will eventually get clogged with dirt and need replacement at more or less specific
intervals. All vulcanized rubber engine mounts will eventually compress to the point of failure, due to the constant forces being exerted on them, again at
a similar approximate time.
What I'm attempting to do with this series is to show parts pattern failures that I'm personally familiar with and seem to follow along make- and
model-specific lines. This approach is solely for your own information, and it is not intended as a critique of any particular auto manufacturer.
In this installment, we'll focus on the frequent failure of crankshaft pulleys – also known as the crankshaft vibration damper – on mid-'90s, Ford-built,
four-cylinder engines, such as the older 1.9-liter found in the Escort model. I have also seen similar failures on other Ford engines but, interestingly
enough, seldom on the company's V-8 designs.
Many manufacturers use a crankshaft pulley with a two-piece design, consisting of the central "hub," an outer "drive ring," and a high-density
rubber composite "absorption layer" sandwiched in between. Variations of this design have been in use for decades with great reliability. It's not uncommon
to see original equipment pulleys still in service on '60s-era vehicles.
The nature of the failure of the pulley design considered in this article has to do with a loss of adhesion between the rubber absorption layer and the
outer ring, hub or both. In other words, the outer ring, which turns the belt driving the engine's accessory pulleys, slips in relation to the inner ring.
This slippage can sometimes result in a misalignment between the two, which will cause crankshaft pulley wobble, when the pulley visibly "wobbles" with the
engine running. It can also cause a constant slip, while the pulley appears to be turning straight and true.
As you can probably imagine, all sorts of trouble would result under such a condition, from low charging system output to poor and inconsistent power
steering assist and air-conditioning operation, as well as higher cooling system operating temperatures and operating noise.
I have actually seen such pronounced slippage that, after crankshaft pulley removal, I could induce it while holding the pulley in my hands. That's even
more amazing when you consider that the unit was still turning concentrically while mounted on the engine!
At any rate, replacement of the pulley on this model is a fairly straightforward part of car maintenance, requiring no special tools – although a
half-inch drive impact gun is helpful for removal of the crankshaft pulley bolt, and a proper torque wrench is helpful for correctly securing it.
Follow the procedure outlined in the service manual when removing the crankshaft pulley, observing all safety precautions, especially relating to raising
and supporting the front of the car. With the right front wheel and splash shield removed, you can see how accessible the pulley is.
This is not uncommon for all makes, especially where early failure of the original part is involved. So it seems that car companies do learn from their
mistakes – or at least their pattern failures.