ASE A1 Engine RepairCylinder Head and Valve TrainMedium
A technician is installing a new camshaft in an overhead cam (OHC) engine. After installing the camshaft and its bearing caps, they begin to tighten the bearing cap bolts. Which of the following tightening procedures is CRITICAL to prevent camshaft damage or premature wear?
- ATighten outer bolts first, then inner bolts, to half torque.
- BTighten all bolts simultaneously to full torque.
- CTighten inner bolts first, then outer bolts, in stages.
- DTighten all bolts in a spiral pattern from center outwards, in stages.
Show answer & explanationAnswer & explanation
Correct answer: D. Tighten all bolts in a spiral pattern from center outwards, in stages.
Tightening camshaft bearing cap bolts in a spiral pattern from the center outwards, in multiple stages, ensures even clamping force. This prevents bending or binding of the camshaft and ensures proper bearing alignment, which is critical for smooth rotation and longevity.
Why the other options are wrong
- A. Tightening outer bolts first would potentially bow the camshaft in the center, leading to damage.
- B. Simultaneous full torque would likely cause uneven stress, potentially bending the camshaft or damaging bearings.
- C. While tightening in stages is good, an inner-to-outer pattern is generally preferred, but a spiral center-out is more specific and often required.
Camshaft Bearing Cap Torque
Camshaft bearing caps must be tightened in a specific, staged, center-out spiral pattern to ensure even clamping pressure and prevent camshaft distortion or bearing damage.
- Prevents camshaft bending
- Ensures even bearing load
- Typically center-out spiral pattern
Memory trick: Center-out spiral, stages small, prevents camshaft's fall.