Chevrolet 40 60 Series Overhaul Manual Download

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5-14 POW ER BRAKE CYLINDER

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Ring

0.0035"

0.0 0 2 "

0.0055"

0.004"

iW W W '-'f^W W S

-J L _ 0.002"

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Fig. 13G~Piston Ring A rran ge m ent and Clearances 12 cu. ft.

Com pressor

Connecting R ods a nd Bearings

Check fit of connecting rod bearing inserts on crankshaft

journals. Clearance between bearings and crankshaft journals

should not exceed

0 0 2 1

C h e ckin g Clearance b y P/astigage M e th od

(Refer to Figure 14G)

To check fit of bearings on crankshaft, install bearing

inserts  into  connecting  rod.  Clean  the  crankshaft  journals
and the inserts so that all oil is removed.  Plastigage is soluble
in  oil,  therefore  oil  will  affect  the  accuracy  of the  reading.

Plastigage is placed on the lower half of the bearings (fig.

14G).

IMPORTANT: To check clearance properly, using Plastigage,

it is essential to not move the connecting rod or crankshaft.

Install connecting rod caps and tighten connecting bolt nuts

to torque. This should flatten Plastigage to not less than

0.0003" or not more than 0.0021". Check measurement on

Plastigage scale (fig. 14G). Replace bearing inserts if clear

ance is excessive, or if bearings are cracked or flaked.

Fig. 14G -C hecking Clearance Using Plastigage

Connecting rod caps are not interchangeable. Position caps

so that locking slots are both located adjacent to same

cap screw.

CAUTION: DO NOT file or lap bearing caps or rods to take

up clearance; always use new bearing inserts if clearances

are excessive.

Crankshaft

Crankshaft journals should not be out-of-round more than

0.001",  ridged  or  scored.  If  grinding  is  necessary,  do  not
grind  fillets  at  ends  of journals.  Connecting  rod  bearing  in
serts  are  available  in  0.010",  0.020",  0.030"  undersize  for
reground  crankshafts.  Check  main  bearing  journals  for
excessive wear.  Dimensions should be such that ball bearing
is  a  press  fit  on journal.

Crankshaft Bearing

Examine bearing for wear or flat spots by rotating races.

If any roughness is detected bearing should be replaced with
new bearing.

C O M P R E S S O R R E P A IR

Discharge Valves a nd Sea ts

1. Remove slight scratches and pits from discharge valve

seats. Use lapping stone, gringing compound, lapping

disc, and valve grinding tool.

2. Place discharge valves on valve seats, install discharge

valve springs in cap nuts, and thread cap nuts firmly
into cylinder head. To test discharge valves for leakage,
connect air line to discharge port in cylinder head. Ap
ply

1 0 0

pounds air pressure to valves and apply soap

suds to discharge valve openings in bottom of cylinder
head. Leakage in excess of a one-inch bubble in one
second is not permissible. If leakage is excessive, leave
air pressure applied. Using a fiber or a hardwood dowel

and  a  light  hammer,  tap  valves  off seats  several  times.
This should improve fit of valve on seat.  Check leakage
around  top of area.  No  leakage is permissible.  Shut off
air  pressure  and  disconnect  line  from  cylinder  head.

Inlet V a lv e s and S e a t s

1. Remove slight scratches or pits from inlet valve seats.

Use lapping stone, grinding compound, lapping disc,
and valve grinding tool. Replace seats that cannot be

repaired. Dimension from the top of the cylinder block

to the inlet valve seat should not exceed 0.145", nor be

less than

1 0 1

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