Fitting Pistons; Fitting Piston Rings - Ford VSG-411 Service Manual

Basic Engine
3. Place a piece of Plastigage on bearing surface across full
width of bearing cap and about l/4 inch off center (Figure 12).
4. Install cap and torque bolts to specifications. Do not turn
crankshaft while Plastigage is in place.
5. Remove cap. Using Plastigage scale, check width of Plas-
tigage at widest point to get minimum clearance. Check at
narrowest point to get maximum clearance. Difference be-
tween readings is taper of journals.
6. If clearance exceeds specified limits on the connecting rod
bearings, try a 0.002 inch undersize bearing in combination
with the standard bearings. Bearing clearance must be within
specified limits. If 0.002 undersize main bearings are used on
more than one journal, be sure they are all installed in cylinder
block side of bearing. If standard and 0.002 inch undersize
bearings do not bring clearance within desired limits, refinish
crankshaft journal, then install undersize bearings.
7. After bearing has been fitted, remove Plastigage, apply light
coat of engine oil to journal and bearings. Install bearing cap.
Torque cap bolts to specifications.
8. Repeat procedure for remaining bearings that require
replacement.
PLACE PLASTIGAGE
FULL WIDTH
OF JOURNAL ABOUT
l/4 INCH OFF CENTER
PLASTIGAGE
\ -1
. I
1 CLEARANCE
IN
-CHECK WIDTH
OF PLASTIGAGE A2868-B
FIG. 12 Installing and Measuring Plastigage
PISTONS, PINS AND RINGS
FITTING PISTONS
Pistons are available for service in standard sizes and the over-
sizes shown in the parts list.
Measure the piston diameter to ensure that the specified clear-
ance is obtained. It may be necessary periodically to use another
piston that is either slightly larger or smaller to achieve the spec-
ified clearance. If none can be fitted, refinish the cylinder to
provide the proper clearance for the piston. When a piston has
been fitted, mark it for assembly in the cylinder to which it was
fitted. If the taper, out-of-round and piston to cylinder bore
clearance conditions of the cylinder bore are within specified
limits, new piston rings will give satisfactory service. If new
rings are to be installed in a used cylinder that has not been
refinished, remove the cylinder wall glaze (Refer to Cylinder
Block, Refinishing Cylinder Walls). Be sure to clean the cylin-
der bore thoroughly.
1. Calculate the size piston to be used by taking a cylinder bore
check. Follow the procedures outlined under Cleaning and
Inspection.
2. Select the proper size piston to provide the desired clearance
(refer to the specifications). The piston should be measured
2-l/4 inches below the dome and at 90' to the piston pin bore.
3. Make sure the piston and cylinder block are at room tem-
perature (70 degrees F.). After any refinishing operation
allow the cylinder bore to cool, and make sure the piston
and bore are clean and dry before the piston fit is checked.
FITTING PISTON RINGS
Three piston rings are fitted, two compression and one oil
control ring.
1. Select the proper ring set for the size cylinder bore.
2. Position the ring in the cylinder bore in which it is going to be
used.
3. Push the ring down into the bore area where normal ring wear
is not encountered.
4. Use the head of a piston to position the ring in the bore so that
the ring is square with the cylinder wall. Use caution to avoid
damage to the ring or cylinder bore.
5. Measure the gap between the ends of the ring with a feeler
gauge (Figure 13). If the ring gap is less or greater than the
specified limits, try another ring set.
P
FIG. 13 Checking Piston Ring Gap
6. Check the ring side clearance of the compression rings with a
feeler gauge inserted between the ring and its lower land
(Figure 14). The gauge should slide freely around the entire
ring circumference without binding. Any wear that occurs will
form a step at the inner portion of the lower land. If the lower
lands have high steps, the piston should be replaced.
FIG. 14 Checking Piston Ring Side Clearance