Honda GX 120 Tech Manual page 10

This engine block must be "as cast" and in factory machined condition. There must be no addition or
subtraction of metal or any other substance to the inside or outside of the cylinder block, crankcase cover,
crankshaft, rod, piston, pin, rings, flywheel or coil with the following exceptions:
A. Removal of rear gas tank brackets is permitted.
B. Removal of governor. Governor system may be partially removed with the exception of the steel gear on the
crankshaft. This gear must remain intact. Governor arm and shaft may be removed, tied forward or altered to
accommodate throttle linkage or return springs.
C. Addition of brackets, fittings etc. to accommodate throttle linkage, tachometer, temperature gauge is allowed.
D. Cylinder Block deck surface non tech
Check bore: 2.366" maximum NOTE:
"Wear Limits/Parts Out Of Service" QMA reserves the right to confiscate 120 Honda engine parts deemed illegal or at
QMA maximum wear limits. EXAMPLE: Cylinder Bore will be 2.366 Max. All measurements taken at top of bore or very
bottom of bore parallel to crank, 90 degrees from crank. Any cylinder block that has one measurement over QMA maximum
wear limits will be taken out of service. If no measurements exceed QMA maximum wear limits the part of block will not be
confiscated. Handler has the right to have confiscated parts returned to them but will be rendered unusable.
Use dial caliper to check bore.
Check stroke: 1.659" Maximum
Measure amount that piston is up or down from block surface at T.D.C. This will be measured at edge or
highest part of piston, not in center or relieved area. This dimension will be:
0.000" Max. – NO PISTON POP UP
Install degree wheel on flywheel. Install pointer in order to read degrees. Locate accurate T.D.C. This should
be done with a positive stop type fixture and not established with indicator alone.
Cam will be checked with indicator reading off the top end of tappets, which will provide zero clearance. The
inverted radius of the top of the tappet presents some problem to get accurate readings and to prevent binding
of indicator stem. Indicator holder and positions are very critical in this operation.
Zero indicator on base circle of cam. Be sure that compression release does not affect zeroing exhaust
indicator. (Zero dial indicator after exhaust bump) ref.
Turning engine in normal rotation, clockwise facing flywheel, take reading at specified opening.
Readings must fall between specified degrees on the following chart.
IN TAKE
0.050"
0.100"
0.150"
0.180 Split
0.200"
Maxlift .227" Peak 104 - 107 ATDC
0.200"
0.180 Split
All measurements taken at top of bore or very bottom of bore.
1.640" Minimum
CAMSHAFT PROFILE LIMITS
Degrees
10 ½ to 14 ATDC
26 ½ to 30 ATDC
45 to 49 ATDC
71 to 76 ATDC
135 to 141 ATDC
EXHAUST
0.050" 206 ½ to 210 ½
0.100" 189 ½ to 193 ½
0.150" 170 ½ to 174 ½
0.180 Split
0.200" 144 to 148
Maxlift .229" Peak 107 ½ - 110 ½ " BTDC
0.200" 70 ½ to 73 ½
0.180 Split
Degrees
BTDC
BTDC
BTDC
BTDC
BTDC
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