Exam 12: Pistons, Rings, and Connecting Rods

Piston diagnosis is being discussed. Technician A says scuffing on one skirt only can be caused by excessive low rpm idling. Technician B says scuffing of the piston skirt can be caused by abnormal combustion or cooling system problems. Who is right?

Ring gaps on an opposed engine design should be faced down.

Technician A says a piston usually has a direction identifying notch that faces the rear of the engine. Technician B says a piston exhibits more wear on its major thrust side. Who is right?

Technician A says that a good piston can be ruined by cleaning the grooves on a wire wheel. Technician B says an old, broken piston ring works well to clean the ring grooves. Who is right?

Technician A says forged pistons are available for heavy-duty or high-performance use. Technician B says that a cast piston is more efficient at dissipating heat.

Name the four forces that combine to push piston rings against the cylinder wall.

Technician A says that the top compression ring groove wears more than the other ring grooves. Technician B says that full floating, piston pin lock rings should be installed with their openings facing up. Who is correct?

The big end of a rod can be up to 0.004" out of round before it needs resizing.

Which is larger: the diameter of the head or crown of the piston or the diameter of the skirt?

Technician A says the piston skirts are cam ground so piston to cylinder wall clearance is maintained as the piston expands with increasing engine temperature. Technician B says that piston skirts have slipper skirts to control expansion. Who is right?

Automobile piston pins are either pressed fit or full floating.

Piston balance is more important with in-line engines than with V-type engines.

What is the name of the style of piston skirt that is cut away on the sides to allow clearance for the crankshaft counterweights?

Why is the piston pin bore offset from the piston centerline?

Most of today's automotive pistons are slipper skirt pistons.

Two technicians are discussing pressed-fit piston pins. Technician A says that a pin press is used to remove piston pins. Technician B says that a rod furnace is used to remove piston pins. Who is right?

Technician A says that cast pistons run cooler than forged pistons. Technician B says that cast pistons are stronger than forged pistons. Who is right?

Technician A says that some piston rings have chamfers or reliefs cut into them to cause them to twist. Technician B says that chrome rings should not be used in out-of-round cylinders. Who is right?

Technician A says that most V6s use offset connecting rods. Technician B says that rods that have been resized must use oversized rod bearings. Who is right?

Technician A says that installing a compression ring upside down can cause oil consumption. Technician B says that the top compression ring groove usually suffers more wear than the other ring grooves. Who is right?