Bore, stroke, piston pin diameter and clutch hub comparison between 156FMI (CG125) and 162FMJ (CG150).
Both engines share the 15 mm wrist pin diameter (unlike CB125 OHC engines which often use a 13 mm or 14 mm pin) and compatible 5-post / 4-post clutch hub splines, so upgrading a 156FMI to a 62 mm (150cc) cylinder kit is a direct bolt-on provided stud spacing matches.
| Parameter | CG125 (156FMI) | CG150 (162FMJ) | Compatibility |
|---|---|---|---|
| Bore × Stroke | 56.5 mm × 49.5 mm (124cc) | 62.0 mm × 49.5 mm (149cc) | Same 49.5 mm stroke — cylinder kit swaps directly |
| Piston Pin Diameter | 15.0 mm | 15.0 mm | Matches standard 15 mm small-end connecting rod |
| Mainshaft / Countershaft Bearings | 6204 / 6202 / 6001 | 6204 / 6202 / 6001 | 100% standard ISO bearing interchange |
Some tall-deck 150cc cylinders are 2 mm taller than standard CG125 blocks and require matched pushrods.
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