Engine Blocks
What two major components are housed and supported by the engine block?
The cylinders and crankshaft.
What is the name of the crankshaft surface that rotates inside a main bearing?
Main journal.
What component connects the piston to the connecting rod?
Wrist pin (piston pin).
Which piston ring is primarily responsible for controlling excess oil on the cylinder wall?
Oil-control ring.
Why is assembly lubricant applied to bearing and crankshaft journal surfaces during engine assembly?
To provide lubrication during initial rotation and startup.
What type of cylinder wear describes a difference in diameter between the top and bottom of a cylinder?
Cylinder taper.
What crankshaft feature helps offset forces produced by the pistons and connecting rods?
Counterweights.
What is the name of the lower portion of a piston that helps guide it within the cylinder?
Piston skirt.
What tool is commonly used to measure piston-ring end gap?
Feeler gauge.
After installing and tightening the crankshaft main-bearing caps, what should a technician check before continuing?
That the crankshaft rotates properly without unexpected binding.
What condition is being checked when a straightedge and feeler gauge are placed across the block deck?
Deck flatness or warpage.
What type of journal wear occurs when its diameter differs between two locations along its length?
Journal taper.
Why must connecting rod caps stay matched to their original connecting rods?
The rod and cap are machined together to create the correct bearing housing.
What is the purpose of the crankshaft thrust bearing or thrust surface?
To control forward and rearward crankshaft movement (end play).
Why must piston orientation marks be checked before installation?
Pistons may have directional features and must be installed in the correct orientation.
A cylinder is noticeably larger when measured front-to-back than side-to-side at the same height. What condition does this indicate?
Cylinder out-of-round.
Why is a deeply scored crankshaft journal a concern even when its overall diameter is within specification?
The damaged surface can disrupt the oil film and damage the bearing.
A piston has heavy scoring and scuffing on its skirt. Name one possible cause.
Insufficient lubrication, overheating, insufficient clearance, or debris.
What measurement does Plastigage help a technician check during bearing installation?
Bearing oil clearance.
After installing a piston and connecting rod, the crankshaft becomes difficult to turn. What should the technician do?
Stop and investigate the recent installation, including bearing clearance, rod-cap orientation, and possible interference.
A cylinder is worn beyond its manufacturer's service limit. Why might installing new piston rings fail to correct the problem?
The worn cylinder may prevent the rings from sealing properly, requiring machining or replacement.
A crankshaft has been ground to a smaller approved journal diameter. What must be changed when it is reassembled?
The bearings must be correctly sized to match the undersize journals and provide proper oil clearance.
A piston diameter measures within specification, but its piston-to-cylinder-wall clearance is excessive. What other measurement should be investigated?
Cylinder bore diameter and wear.
A connecting rod bearing has deep scoring and embedded metal particles. What engine system should be investigated for contamination?
The lubrication system, including the engine oil and oil passages.
A crankshaft journal measures within specification, but its assembled bearing oil clearance is excessive. Name two possible causes that should be investigated.
Incorrect bearing size, worn bearing, incorrect bearing housing dimensions, or assembly errors.