Engine mechanism fundamentals To which specific part of the crankshaft is the lower end of the connecting rod attached in an internal combustion engine?

Introduction / Context:
The crank–connecting-rod mechanism converts reciprocating piston motion into rotary motion. Understanding which features mate together (small end, big end, crankpin journal, main journal) is foundational for engine assembly, lubrication, and failure analysis.

Given Data / Assumptions:

• The connecting rod has two ends: a small end (to the piston pin) and a big end (to the crankshaft).
• The crankshaft has main journals (support in bearings) and crankpin journals (offset throws) joined by webs/arms and counterweights.
• Pressurized oil is supplied to journals for hydrodynamic lubrication.

Concept / Approach:
The big end of the rod does not clamp directly to a web or counterweight; it rides on the crankpin journal, often simply called the journal in engine service literature. A replaceable bearing shell (or needle/roller in some engines) separates the rod big end from the journal surface, maintaining an oil film.

Step-by-Step Solution:
Identify mating components: piston ↔ small end ↔ piston pin; crankshaft ↔ big end ↔ crankpin journal.The crank arm (web) connects the crankpin to the main journal but is not a bearing surface for the rod.Therefore, the lower (big) end of the connecting rod attaches to the crankshaft at its crankpin journal.

Verification / Alternative check:
Exploded engine diagrams or service manuals label the bearing location at the crankpin journal; torque specs refer to big-end cap bolts around this journal.

Why Other Options Are Wrong:
Big end (option a) names the rod's end, not the crankshaft feature it mounts on.

Crank arm (option b) is a web, not the bearing surface.

Small end (option d) couples to the piston pin, not the crankshaft.

Counterweight (option e) balances inertia; it is not a bearing surface.

Common Pitfalls:
Confusing main journals (supporting the crank in the block) with crankpin journals (supporting the rod). Mixing terminology can lead to errors in parts ordering and measurement.

Final Answer:
journal