The upper piston compression ring can be...

Question 1 of 270705eccefa1bacbc34ba4d47538

The upper piston compression ring can be protected from overheating by a heat dam. This physical concept is shown in the illustration and designated by the figure lettered as __________. See illustration MO-0017.

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Question 1 of 27070

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🔍 Key Concepts

• Heat dam on a piston: a narrowed or recessed area above the top ring land that reduces heat conduction from the crown to the top ring groove. • Difference between cooling passages/galleries (which carry oil or water) and a simple change in piston outer diameter/shape. • Location of the upper compression ring groove and how metal contact with the cylinder wall above it affects ring temperature.

💭 Think About

• Look closely at each piston sketch and find which one shows the metal surface above the top ring not fully touching the cylinder wall. • Ask yourself: which figure changes only the shape/diameter of the piston land above the ring, instead of adding extra parts, holes, or cooling passages? • Eliminate any figures that clearly show active cooling (oil, passages, or valves), because a heat dam is a passive shape feature, not a flow system.

✅ Before You Answer

• Identify exactly where the top compression ring groove is in each figure, then focus only on the metal immediately above that groove. • Verify that the candidate figure shows a reduced contact area with the liner (a step, groove, or smaller diameter above the ring). • Confirm that there are no oil lines, drilled galleries, or moving parts associated with the feature you pick; it should be just a geometric change in the piston crown/land.