Tech Q&A & Workshop Fitment Notes

Roller dimensions (20×12 mm) and clutch bell splines are interchangeable across Blue Core 155 VVA engines, but V1 NMAX (2DP) and V2 NMAX / Aerox (B65 / BBP) use different V-belt lengths and primary sheave angles. Installing a 2DP belt on a B65 case causes high-RPM slip.

In over 80% of Error Code 12 cases on Smart Motor Generator (SMG) models, the Crankshaft Position Sensor (CKP) and stator windings are still intact — the culprit is high contact resistance or melting at the white 3-pin phase connector under the right side cover. Only replace the stator/rotor assembly if phase resistance or insulation to ground fails spec.

At 10,000 km: replace spark plug (CPR8EA-9), air filter element, CVT case filter foam, and gear oil drain crush washer. At 20,000 km: replace the CVT V-belt, variator rollers (6 pcs), cam sliders (3 pcs), fuel pump O-ring, and inspect valve clearance (Intake 0.10–0.14 mm / Exhaust 0.18–0.22 mm).

Count the CVT cover bolts or measure crankshaft-to-clutch shaft distance: Short-case GY6 125/150 (10-inch rear wheel, 7 or 8 bolts) uses 743-20-30; Long-case GY6 125/150 (12/13-inch rear wheel, 8+1 center bolt) uses 835-20-30 or 842-20-30.

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.

Fork oil seals are standardized by Inner Diameter × Outer Diameter × Thickness (e.g., 26×37×10.5 mm for 26mm scooter forks, 31×43×10.3 mm for 31mm forks, 33×46×11 mm for 33mm forks). Recurring leaks after seal replacement are almost always caused by rust pits on the chrome stanchion or installing the double-lip seal upside down.