Piston and Connecting Rod, Cleaning, Inspection and Repair

TM 10-3930-630-34

TA067457

Figure 11-17. Piston and connecting rod, removal, and installation.

(4) Check ring groove widths as illustrated in

b. Disassembly.

figure 11-20.

(1) Disassemble the piston and connecting rod

(a) Top ring groove must measure 0.081

in numerical sequence as illustrated in figure 11-18.

to 0.080 inch (2.05 to 2.03 mm). Maximum wear limit is

(2) Rod bolt (8), nut (7), bearing cap (9) and

0.083 inch (2.10 mm).

bearing shells (10) were removed when connecting rod

(b) Second and third ring groove must

was removed from crankshaft.

measure 0.0965 to 0.0955 inch (2.45 to 2.42 mm).

Maximum wear limit is 0.0985 inch (2.50 mm).

11-18. Piston and Connecting Rod, Cleaning,

(c) Fourth ring groove width must

Inspection and Repair

measure 0.189 to 0.188 inch (4.80 to 4.77 mm).

a. Clean parts in cleaning solvent (Fed. Spec. P-

Maximum wear limit is 0.191 inch (4.85 mm).

D-680).

Check piston rings as follows:

b. Inspect rings for worn or broken condition.

(1) Measure top piston ring width. Width must

be 0.078 to 0.077 inch (1.98 to 1.95 mm). Minimum

c. Check for carbon deposits on piston walls and in

wear limit width is 0.075 inch (1.90 mm).

ring grooves. Clean carbon.

(2) Measure second and third ring widths.

d. Inspect inside of piston for cracks and other

Width must be 0.094 to 0.093 inch (2.38 to 2.36 mm).

damage. Check drilled holes in piston walls and clean if

Minimum wear limit width is 0.091 inch (2.29 mm).

necessary.

(3) Measure fourth ring width. Width must be

e. Check piston as follows:

0.188 to 0.184 inch (4.77 to 4.68 mm). Minimum wear

(1) Attach a one-half inch (12.7 mm) long strip

limit width is 0.182 inch (4.63 mm).

of feeler stock (fig. 11-19) 0.003 inch (0.076 mm) thick

(4) Check ring-to-land clearance (fig. 11-20)

to a spring scale of approximately 15 pounds capacity

using a feeler gage.

(fig. 11-19).

(a) Top ring clearance must not exceed

(2) Insert piston and feeler stock in cylinder

0.008 inch (0.203 mm).

bore. Withdraw the feeler stock and check pull on

(b) Second and third ring clearance must

spring scale. Pull must be 5 to 10 pounds (2.77 to 4.53

not exceed 0.006 inch (0.152 mm).

kg). If pull is less, replace piston.

(c) Fourth ring clearance must not

(3) Measure piston skirt diameter. Diameter

exceed 0.009 inch (0.228 mm).

must be 3.4120 to 3.4170 inches (86.6 to 86.7 mm).

11-13