| 428 | 520 | |
|---|---|---|
| Pitch | ½" (12.7 mm) | ⅝" (15.875 mm) |
| Inner width | 5/16" (7.94 mm) | ¼" (6.35 mm) |
| Roller diameter | 0.335" (8.51 mm) | 0.400" (10.16 mm) |
| Typical engines | 110–250cc pit bikes, trail bikes and small ATVs | 250cc+ dirt bikes, most sport ATVs |
The key difference
The 520 has a longer pitch and bigger rollers, so for the same ratio each link and roller carries its load over a larger area, which is why 520 is used once engines get bigger. Oddly, the 520 is narrower inside than the 428 – the “20” and “28” describe width, and the 520’s strength comes from its bigger pitch and rollers.
Why people convert 428 to 520
- A big-bore kit or engine swap (for example a 150–250cc engine in a frame built for 125cc).
- More sprocket choice – many sport ATVs and big dirt bikes use 520.
What a conversion involves
Both sprockets and the chain change together – nothing carries over. Check that the front sprocket with the right spline exists in 520, that the chain clears the swingarm and guard (rollers are bigger), and recalculate the chain length, because a ⅝" pitch needs fewer links for the same distance.
For a stock 110–125cc engine, a good-quality 428 chain is plenty. Converting only makes sense when the power or the parts situation demands it.