Top End Specifications For Your 1997-2001 Yamaha YZ125
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General Engine Specifications
| Displacement | 124 cc |
| Bore x Stroke | 54 x 54.5mm (2.126 x 2.146 in.) |
| Compression Ratio | |
| – 1994 – 1995 | 9.0 – 10.1:1 |
| – 1996 – 1997 | 8.5 – 10.4:1 |
| – 1998 – 1999 | 8.9 – 10.9:1 |
| – 2000 – 2001 | 8.7 – 10.:1 |
| Lubrication System | |
| System Type | Fuel/Oil |
| Pre-mix Ratio | 30:1 |
Engine Service Specifications
| New – mm (in.) | Service Limit – mm (in.) | |
| Cylinder Head Warpage Limit | – | 0.03 90.0012) |
| Cylinder Bore Inside Diameter | ||
| Standard Cylinder | 54.000 – 54.014 (2.1260 – 2.1266) | 54.1 (2.130) |
| Cylinder Mark A | 54.000 – 54.002 (2.1260 – 2.1261) | – |
| Cylinder Mark B | 54.004 – 54.006 (2.1261 – 2.1262) | – |
| Cylinder Mark C | 54.008 – 54.010 (2.1246 – 2.1247) | – |
| Cylinder Mark D | 54.012 – 54.014 (2.1265 – 2.1266) | – |
| Piston Outside Diameter | ||
| Standard Piston | 53.957 – 53.972 (2.1263 – 2.1249) | – |
| Piston Mark A | 53.957 – 53.960 (2.1263 – 2.1244) | – |
| Piston Mark B | 53.961 – 53.964 (2.1244 – 2.1246) | – |
| Piston Mark C | 53.965 – 53.968 (2.1246 – 2.1247) | – |
| Piston Mark D | 53.969 – 53.972 (2.1248 – 2.1249) | – |
| Piston Measuring Point From Base of Piston | 10.00 (0.39in) | – |
| Piston-to-Cylinder Clearance | 0.040 – 0.045 (0.0016 – 0.0018 | 0.1 (0.004) |
| Piston Ring-to-Groove Clearance* | 0.030 – 0.070 (0.0012 – 0.0028) | 0.1 (0.004) |
| Piston Ring Groove Width | 1.00 (0.040) | – (0.051) |
| Piston Ring End Gap (Installed) | ||
| 1994 – 1995 | 0.50-0.65 (0.020 – 0.026) | 0.80 (0.031) |
| 1996 – 2001 | 0.50-0.70 (0.020 – 0.028) | 1.2 (0.047) |
| Piston Pin Outside Diameter | ||
| 1994 – 1995 | 15.995 – 16.000 (0.6297 – 0.6299) | 15.975 (0.6289) |
| 1996 – 2001 | 14.995 – 15.000 (0.5904 – 0.5906) | 14.975 (0.5896) |
| Piston Pin Bore | NA | NA |
| Reed Valve* | ||
| Bending Limit | – | 0.2 (0.008) |
| Stopper Height | 7.4 – 7.8 (0.291 – 0.307) | – |
| *2000 – 2001 | ||
| Piston Ring-to-Groove Clearance | 0.035 – 0.080 (0.0014 – 0.003) | 0.1 (0.004) |
| Reed Valve Stopper Height | 8.2 – 8.6 (0.323- 0.339) | – |
Engine Top End Torque Specifications
| ft.-lb | in.-lb. | N•n | |
| Water Pump Drain Bolt | |||
| – 1994 – 1996 | – | 78 | 8.8 |
| – 1997 – 2001 | – | 88 | 10 |
| Cylinder Base Nuts | 21 | – | 28 |
| Cylinder Head Nuts | 21 | – | 28 |
| Cylinder Head Hanger Nuts | 25 | – | 34 |
| Power Valve | |||
| – 1994 – 1995 Operating Rod Screw | – | 44 | 5 |
| Arm Screw | – | 44 | 5 |
| – 1996 – 2001 Operating Rod Screw | – | 35 | 4 |
| Arm Screw | – | 35 | 4 |
| Intake Manifold Mounting Bolts | – | 88 | 10 |
| Spark Plug | 15 | – | 20 |
