Which condition can cause local hot spots on a combustion cam?

Which condition can cause local hot spots on a combustion cam?

• A. Overly tight tolerances
• B. Excessive lubrication
• C. Repairs or sloppy weld beads which protrude internally
• D. Improper piston ring fit

Answer: (C)

Local hot spots on a combustion cam come from irregularities that create concentrated contact stress and friction. If repairs or weld beads are done inside the cam bore or on internal surfaces and protrude into the path the follower rides in, they become raised features. As the cam lobe and follower sweep past, these protrusions press harder against the follower, producing high local contact pressure. That localized rubbing converts more energy to heat in a small area, causing a hot spot and accelerated wear there. Proper smoothing of any welded areas and ensuring a clean, uniform surface eliminates these high-pressure spots. The other conditions don’t typically produce a distinct hot spot: overly tight tolerances tend to cause overall binding and uniform wear rather than a localized heating spot; excessive lubrication generally reduces friction and heat; improper piston ring fit affects the piston area, not the cam’s contact surface.

Local hot spots on a combustion cam come from irregularities that create concentrated contact stress and friction. If repairs or weld beads are done inside the cam bore or on internal surfaces and protrude into the path the follower rides in, they become raised features. As the cam lobe and follower sweep past, these protrusions press harder against the follower, producing high local contact pressure. That localized rubbing converts more energy to heat in a small area, causing a hot spot and accelerated wear there. Proper smoothing of any welded areas and ensuring a clean, uniform surface eliminates these high-pressure spots.

The other conditions don’t typically produce a distinct hot spot: overly tight tolerances tend to cause overall binding and uniform wear rather than a localized heating spot; excessive lubrication generally reduces friction and heat; improper piston ring fit affects the piston area, not the cam’s contact surface.