Order of checks
| Check | Values | Why it comes first |
|---|---|---|
| 1. Crankshaft bore | 3/4" · 1" | Decides whether the driver pulley mounts on the engine at all |
| 2. Series / belt | 30 Series → 669 belt | The belt is set by the series; you do not choose it separately |
| 3. Driven sprocket pitch | #35 · #420 | Has to match the chain and rear sprocket already on the bike |
| 4. Frame clearance | Varies by machine | The converter is wider than a bare clutch — check before ordering |
1. Crankshaft bore — the only unforgiving number
Measure the engine output shaft with a caliper. Mini bike engine cranks come in 5/8" (16 mm), 3/4" (19 mm) and 1", and there is no safe adapter between them. Our 30 Series TAV2 torque converter covers the two sizes a converter build normally sits on — 3/4" and 1" — and the kits are otherwise identical.
Do not order off engine size. The same nominal displacement appears with different crankshafts depending on the production run, which is why every drivetrain part on this site is sold in bore variants. If you measure 5/8", a converter is not your part — start from the 420 chain, clutch & sprocket kit, which covers 5/8" and 3/4".
2. Series and belt
Series is not a performance grade you pick — it is a size class, and it determines the belt.
| Series | Belt | Belt style | Typical class |
|---|---|---|---|
| 30 Series | 669 | 3/4" asymmetric | Mini bike / go kart, single-cylinder clone engines |
| 40 Series | Wider — see kit spec | 7/8" symmetric | Heavier vehicles, higher sustained load |
For a mini bike on a 99cc–212cc clone engine, the 30 Series is the size class that matches, and the kit ships with its 669 belt included. Ordering a 40 Series because it sounds stronger buys width and weight the frame usually has no room for.
3. Driven sprocket pitch
The converter's driven side carries a sprocket, and that sprocket has to share a pitch with the chain and rear sprocket already on the bike. Our kit includes both #420 and #35 sprocket options, so the pitch decision does not become a second order. If you are not sure which pitch you are running, identify it first in what size chain a mini bike uses.
4. What comes in the box
Driver pulley assembly · driven pulley components · 669 drive belt · aluminium mounting plate · sprocket options for #420 and #35 · hardware. It is a complete 30 Series TAV2 replacement, so the usual second shopping trip for a backing plate or belt does not happen.
By machine
Background on how the converter sits in the rest of the drivetrain: clutch, chain and sprocket fitment.
Wrong-part traps
- Ordering by engine size instead of measuring the crank. 3/4" and 1" both appear on 212cc-class engines. Measure.
- Assuming 40 Series is the upgrade. It is a size class for heavier vehicles, not a performance tier — and it is wider than most mini bike frames allow.
- Keeping a #35 rear sprocket and fitting a #420 driven sprocket. Pitch has to be consistent from the converter all the way to the rear wheel.
- Not checking frame clearance. A converter is substantially wider than the bare clutch it replaces — measure before the box arrives.
- Reusing the old chain at the new length. Converter output sits in a different place than a clutch sprocket, so chain length usually changes.
FAQ
What does a torque converter do on a 212cc engine?
It replaces the fixed centrifugal clutch with a variable-ratio belt drive. Instead of one engagement point, the drive ratio changes continuously with load and RPM, giving smoother pull from a standstill and a taller ratio at speed.
What size torque converter fits a mini bike?
For 99cc to 212cc clone engines, the 30 Series (TAV2) is the matching size class and it runs a 669 belt. Choose the kit by your crankshaft bore — 3/4" or 1" — and by the chain pitch already on the bike.
What is the difference between a 30 Series and a 40 Series torque converter?
They are different size classes. The 30 Series uses a 3/4" asymmetric belt (669) and suits mini bikes and go karts. The 40 Series uses a wider 7/8" symmetric belt for heavier vehicles under sustained load, and generally needs more frame room.
How do I know if I need a 3/4" or 1" bore?
Measure the engine output shaft with a caliper. The two sizes are not interchangeable and no shim or adapter makes the mismatch safe, so this is the first thing to confirm before ordering.
Does the kit include the belt?
Yes — the 30 Series kit ships with its 669 drive belt, driver and driven pulley assemblies, mounting plate, hardware, and sprocket options in both #420 and #35.
Parts that fit
Shop drivetrain parts 30 Series TAV2 torque converter — 3/4" or 1" bore
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