To ensure accurate main bearing oil clearance measurements during an engine rebuild, which step should be performed?

• A. Coat all bearing surfaces with fresh oil
• B. Torque all bearing cap housings and the bearing being measured
• C. Measure clearances using a plastigauge
• D. Allow the crankshaft to rest on v-blocks

Answer: (B)

The key idea is that bearing clearances must be measured with the caps seated and clamped as they will be in service. Torquing all bearing cap housings and the bearing being measured applies the correct preload and ensures the bearing sits squarely against the journal. This seating and clamp load are what the plastigauge reading reflects, so the measured clearance matches what the engine will actually see once rebuilt. If the caps aren’t torqued, the bearing can shift or not be fully seated, giving an unreliable reading that could be too large or too small. By torquing to spec, you reproduce real operating conditions and obtain an accurate clearance. Coating bearing surfaces with oil or leaving the crank unsupported doesn’t establish that clamp condition, so those steps don’t yield a trustworthy measurement.