Ford Ranger Maintaince And Repair Manual page 483

HOW TO USE THIS BOOK
Crankshaft
Inspect the crankshaft for visible signs of wear or damage. All of the journals should be perfectly round and
smooth. Slight scores are normal for a used crankshaft, but you should hardly feel them with your fingernail.
When measuring the crankshaft with a micrometer, you will take readings at the front and rear of each journal,
then turn the micrometer 90 degrees and take two more readings, front and rear. The difference between the
front−to−rear readings is the journal taper and the first−to−90 degree reading is the out−of−round
measurement. Generally, there should be no taper or out−of−roundness found, however, up to 0.0005 in.
(0.0127mm) for either can be overlooked. Also, the readings should fall within the factory specifications for
journal diameters.
If the crankshaft journals fall within specifications, it is recommended that it be polished before being
returned to service. Polishing the crankshaft insures that any minor burrs or high spots are smoothed, thereby
reducing the chance of scoring the new bearings.
Pistons and Connecting Rods
PISTONS
The piston should be visually inspected for any signs of cracking or burning (caused by hot spots or
detonation), and scuffing or excessive wear on the skirts. The wrist pin attaches the piston to the connecting
rod. The piston should move freely on the wrist pin, both sliding and pivoting. Grasp the connecting rod
securely, or mount it in a vise, and try to rock the piston back and forth along the centerline of the wrist pin.
There should not be any excessive play evident between the piston and the pin. If there are C−clips retaining
the pin in the piston then you have wrist pin bushings in the rods. There should not be any excessive play
between the wrist pin and the rod bushing. Normal clearance for the wrist pin is approx. 0.001−0.002 in.
(0.025mm−0.051mm).
Measure the piston's outer diameter, perpendicular to the wrist pin, with a micrometer
Use a micrometer and measure the diameter of the piston, perpendicular to the wrist pin, on the skirt.
Compare the reading to its original cylinder measurement obtained earlier. The difference between the two
readings is the piston−to−wall clearance. If the clearance is within specifications, the piston may be used as is.
If the piston is out of specification, but the bore is not, you will need a new piston. If both are out of
specification, you will need the cylinder rebored and oversize pistons installed. Generally if two or more
pistons/bores are out of specification, it is best to rebore the entire block and purchase a complete set of
oversize pistons.
INSPECTION 477