Cylinder Bore And Piston Measurement - Hummer H1 Service Manual

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2-62 Engine
Check the pipe plugs at the sides and front of the block
(Figure 2-103). Replace any plugs that are loose or leaking.
Coat replacement plug threads with Permatex #2, or high temp
silicone sealant before installation.
BLOCK PLUG
PLUG
Figure 2-103: Cylinder Block Valve and Plug
Locations

Cylinder Bore and Piston Measurement

Check surface flatness of the cylinder block deck with a
straightedge and feeler gauge (Figure 2-104). Deck surface
flatness must not vary by more than 0.002 in. (0.05 mm) in any
six inch (15 cm) length, or 0.006 in. (0.15 mm) overall. Re-
place the cylinder block if deck flatness is not within stated
limits. Do not attempt to salvage a block by machining the
deck surface. This practice will result in valve-to-piston con-
tact.
STRAIGHTEDGE
DOWEL PIN
CYLINDER BLOCK DECK
Figure 2-104: Checking Deck Flatness
OIL
SAFETY
VALVE
OIL PRESSURE
REGULATOR VALVE
DOWEL PIN
Check condition of the cylinder head and front cover dowel
pins (Figure 2-104). Remove and replace any pins that are
loose.
Inspect the main bearing saddles, bearing caps, front cover sur-
face, block webs, and pan rails (Figure 2-105). Replace the
block if cracks, severe scoring, or distortion is evident at any
point.
Measure degree of wear and taper in each cylinder bore with
bore gauge J–8087 (Figure 2-106).
a. Refer to the Service Piston and Cylinder Bore Specifi-
cations data at the end of this section for bore dimen-
sions.
b. Center the bore gauge in the cylinder and zero the dial
indicator (Figure 2-106).
PIPE
c. Work the gauge slowly up and down the cylinder
PLUGS
from top to bottom. Take measurements at cylinder
axis points "A" and "B" (Figure 2-107). Note that
most wear occurs in the top 2 1/2 in. (63.5 mm) of the
cylinder.
WEB
Figure 2-105: Rail, Web, Bearing Inspection Points
NOTE: Cylinder number 7 and 8 require an additional 0.0005
in. (0.013 mm) for piston clearance. Take this into account
when checking bore wear.
d. Maximum allowable service wear and taper is 0.005
in. (0.013 mm).
e. Rebore the cylinder and replace the pistons if wear
and taper exceed allowable service limits.
NOTE: Replace the cylinder block if bore diameter exceeds
4.075 in. (103.521 mm) on cylinder 1-6 and 4.076 in. (103.534
mm) on cylinders 7 and 8.
BEARING CAP
PAN RAIL
BEARING
SADDLES
CAMSHAFT
THRUST PLATE
SURFACE
®
FRONT COVER
SURFACES