How to identify the main thrust position of the crankshaft
Jan 23, 2026| 
The crankshaft's "thrust position" (also called the "thrust bearing location") refers to the one and only main bearing cap (usually on the cylinder block) and its corresponding main bearing seat that is equipped with thrust bearings (thrust washers).
Its function is to limit excessive axial (fore-and-aft) movement of the crankshaft while maintaining the proper axial operating clearance.
Identification Methods：
Observe the Width of the Bearing Cap/Seat (The Most Visual Method)
Action:
With the cylinder block inverted or by observing the main bearing caps, typically only one bearing seat (or cap) is visibly wider than all the others. This is the main thrust position.
Observe the Crankshaft Main Journal Thrust Faces (Direct Evidence)
Feature: Locate the widest main journal on the crankshaft. Usually, both sides of this journal feature wider, smoothly machined disc faces (much larger than the fillet radii leading to the connecting rod journals).
Check the drawing: The position with the smallest tolerance of the main bearing is the main thrust
Common misunderstandings and precautions
Not All Main Bearings Have the Thrust Function: In the vast majority of engines, only one main bearing serves as the thrust bearing. Never install thrust washers in the wrong location or in multiple locations.
Pay Attention to Orientation: The grooved/oil side of the thrust washer must face the rotating friction surface of the crankshaft (i.e., outward) to ensure lubrication.
Judging a New/Rebuilt Engine: For a brand-new or freshly rebuilt engine that hasn't run, the difference in bearing seat width is the primary clue.
The Manual is Final: Engine designs vary significantly. Always defer to the specific service manual for the engine model.