Crankshaft Quality Has Gone Downhill
Question: My Mercury Topaz with 50,127 miles on it began knocking recently and was diagnosed as having a worn crankshaft. I can’t find anyone who has ever replaced a crankshaft with under 150,000 miles on it. I have babied this car, never driving over 60 m.p.h. and changed the oil every 3,500 miles. Ford has refused to do anything. I am going to small claims court for the $900 repair. What should a person reasonably expect from a crankshaft?--R.D.B.
Answer: You can reasonably expect a crankshaft to last more than 100,000 miles, but there will always be a few unlucky guys like you who get stiffed with a premature failure. It is a bitter pill to swallow for every motorist who has had to overhaul an engine that should still be in its prime.
The crankshaft is the heart of the engine, a very carefully machined shaft that must be precisely balanced and capable of converting the full force of the engine’s reciprocating pistons to a circular motion.
The best crankshafts are usually drop-forged, a forming process in which the metal grain is oriented for maximum strength. But increasingly, crankshafts are formed more cheaply by the casting of molten steel, resulting in the metal having a weaker crystalline structure.
So, for all of the high technology and electronics packed into modern cars, the longevity and value of the product sometimes comes down to processes that a village blacksmith might have been familiar with 100 years ago.
In addition to the crankshaft production method, the quality of the design has an important bearing on how long it lasts. The key factors are the number of journal bearings that support the crankshaft and the precision with which the crankshaft was balanced at the factory. Quite possibly, your crankshaft was poorly balanced and eventually wore out the bearings.
I doubt you will ever get to the bottom of why the crankshaft failed. Ford denies that the Topaz has a history of such failures. Crankshaft failures also result sometimes from a loss of lubrication or overheating, either of which can be traced to a variety of problems. An oil pump failure or a clogged oil passage are typical in crankshaft failures.
Unfortunately, it seems that your babying of the car helped little. In fact, driving a car timidly seldom does anything to preserve it. The oil changes were certainly a good idea, though.
