What's the symptom?
If you mean it's moving forward and backward, that is controlled by one of the crankshaft bearings called the thrust bearing. On some engines those are selective fit inserts that are next to but not part of the main bearing. In most engines that is a main bearing with two sides folded down to form the thrust surfaces. Clearance between the thrust bearing and the thrust surfaces on the crank are measured in thousandths of an inch. Excessive wear will let the crank move enough to push out the rear main oil seal on some engines, and to allow the counterweights to hit the engine block webbing and make a knocking noise. That noise can occur more often when accelerating because the torque converter can balloon up from increased fluid pressure and push the crank forward. The same can happen on cars with manual transmissions when you push on the clutch. That puts forward pressure on the crank too.
The biggest cause of thrust bearing wear is using low grade engine oil or not changing the oil at recommended intervals. There were also two instances where the wear was caused by insufficient heat treating to harden the crankshaft. It was the thrust surface of the crankshaft that wore away, not the relatively soft bearing. The first was on Ford V-8 engines around 1972. The second case was the Chrysler 3.3L V-6 engines in 1989. The Chrysler engines were all taken care of under warranty. It took the mechanic less than six hours to pull the engine out replace the crankshaft, wash the engine compartment, reinstall the engine, and tie up any loose ends.
Friday, February 4th, 2011 AT 11:07 PM