SERVICE INFORMATION
GX390
mm (in)
Part Item Standard
Service
limit
Engine Maximum speed (at no load)
3,850 ± 150 min
-1
(rpm)
–
Idle speed
1,400 ± 150 min
-1
(rpm)
–
Cylinder compression
0.51-0.69 MPa (5.2-7.0 kgf/cm
2
, 74-100
psi) / 600 min
-1
(rpm)
–
Cylinder head Warpage – 0.10 (0.004)
Cylinder Sleeve I.D. 88.000 – 88.017 (3.4646 – 3.4652) 88.170
(3.4710)
Piston Skirt O.D. 87.975 – 87.985 (3.4635 – 3.4640) 87.85
(3.459)
Piston-to-cylinder clearance 0.015 – 0.042 (0.0006 – 0.0016) 0.12 (0.005)
Piston pin bore I.D. 20.002 – 20.008 (0.7875 – 0.7877) 20.042
(0.7891)
Piston pin Pin O.D. 19.994 – 20.000 (0.7872 – 0.7874) 19.950
(0.7854)
Piston pin-to-piston pin bore clearance 0.002 – 0.014 (0.0001 – 0.0006) 0.08 (0.003)
Piston rings Ring side clearance Top 0.015 – 0.060 (0.0006 – 0.0024) 0.15 (0.006)
Second 0.030 – 0.060 (0.0012 – 0.0024) 0.15 (0.006)
Ring end gap Top 0.200 – 0.350 (0.0079 – 0.0138) 1.0 (0.04)
Second 0.350 – 0.500 (0.0138 – 0.0197) 1.0 (0.04)
Oil (side rail) 0.2 – 0.7 (0.01 – 0.03) 1.0 (0.04)
Ring width Top 1.160 – 1.190 (0.0457 – 0.047) 1.140
(0.0449)
Second 1.160 – 1.175 (0.0457 – 0.0463) 1.140
(0.0449)
Connecting rod Small end I.D. 20.005 – 20.020 (0.7876 – 0.7882) 20.07
(0.790)
Big end side clearance 0.1 – 0.4 (0.004 – 0.016) 1.0 (0.04)
Big end I.D. 36.025 – 36.039 (1.4183 – 1.4189) 36.07
(1.420)
Big end oil clearance 0.040 – 0.064 (0.0016 – 0.0025) 0.12 (0.005)
Crankshaft Crank pin O.D. 35.975 – 35.985 (1.4163 – 1.4167) 35.93
(1.415)
Crankshaft runout – 0.1 (0.003)
Cylinder barrel
(Crankcase)
Camshaft bearing I.D. 16.000 – 16.018 (0.6299 – 0.6306) 16.05
(0.632)
Crankcase cover Camshaft bearing I.D. 16.000 – 16.018 (0.6299 – 0.6306) 16.05
(0.632)
Valves Valve clearance IN 0.15 ± 0.02 –
EX 0.20 ± 0.02 –
Valve stem O.D. IN 6.575 – 6.590 (0.2588 – 0.2594) 6.44 (0.254)
EX 6.535 – 6.550 (0.2572 – 0.2578) 6.40 (0.252)
Valve guide I.D. IN/EX 6.600 – 6.615 (0.2598 – 0.2604) 6.66 (0.262)
Guide-to-stem clear-
ance
IN 0.010 – 0.040 (0.0004 – 0.0016) 0.11 (0.004)
EX 0.050 – 0.080 (0.0020 – 0.0032) 0.13 (0.005)
Valve seat width 1.0 – 1.2 (0.04 – 0.05) 2.0 (0.08)
Valve spring free length 39.0 (1.54) 37.5 (1.48)
Valve spring perpendicularity – 1.5° max.
Camshaft Cam height IN 32.498 – 32.698 (1.2794 – 1.2873) 32.198
(1.2676)
EX 31.985 – 32.185 (1.2592 – 1.2671) 29.886
(1.1766)
Camshaft O.D. 15.966 – 15.984 (0.6286 – 0.6293) 15.92
(0.627)
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