A direct-fit 3660 brushless motor for 1/8 four-wheel-drive brushless street trucks.
If your truck feels slower than it used to, the motor is usually the reason.
Brushless motors do not fail all at once. The bearings dry out and start to whine, repeated heat cycles weaken the rotor, and fine grit from a dusty run works its way inside the can. The symptoms are easy to recognise: the truck feels flat off the line, the motor runs hotter than it did, and top speed drops even though you changed nothing in the setup. A fresh motor fixes all three at once — and it is a swap you can finish on a bench in a few minutes.
- ✓A worn bearing is a loud bearing — the first sign is usually a whine, or a gritty feel when you spin the shaft by hand.
- ✓Heat costs power — enough hot runs and the rotor loses strength, so the truck gets slower on the same gearing.
- ✓Grit adds drag — dust inside the can drags on the rotor, so you get less run time from the same pack.
- ✓Same footprint, fresh power — this is a 3660 can with a 5mm shaft, so it bolts onto the same motor plate as the original.
3900Kv: the wind that makes a street truck quick.
Kv tells you how fast a motor turns for every volt you feed it. On a 3S pack at 11.1V, a 3900Kv motor spins at roughly 43,000 rpm with no load — the number that becomes wheel speed once it passes through your pinion, spur gear and differential. Combine that with a 4-pole rotor, which produces torque more smoothly than a 2-pole design, and the truck pulls hard from a standstill and keeps building speed down the straight.
Voltage in, rpm out — the motor is where electrical power becomes the wheel speed you feel.
Machined aluminium, hardened steel, plated connectors.
The housing is CNC machined aluminium, which holds the bearings true and moves heat away from the windings. Inside, high-purity copper windings sit on a sintered 4-pole rotor carried by precision ball bearings at both ends. The output shaft is hardened steel at 5 mm — the standard for this motor size — and the leads end in 4 mm gold-plated bullet connectors that push straight into a matching speed control.
End bell, hardened 5 mm shaft and 4 mm gold-plated bullets — the details that decide how long a motor lasts.
- ✓CNC machined aluminium housing. Rigid, dimensionally stable, and it helps pull heat out of the windings.
- ✓Precision ball bearings. Smooth rotation at high rpm and a longer service life than a bushing design.
- ✓Hardened 5 mm steel shaft. Takes the load of the pinion without flexing — a 5 mm bore pinion is required.
- ✓4 mm gold-plated bullet connectors. Already fitted to the leads, so there is nothing to solder.
Three steps, one hex driver.
There is no rewiring and no soldering. The motor bolts to the same motor plate, and the leads plug straight into the speed control — which makes this a job you can do between runs, not a rebuild.
On the plate, pinion meshed to the spur gear — the whole swap takes a few minutes.
Will it fit your truck?
This is a 3660 can with a 5 mm shaft and 4 mm bullet connectors — the same fitment class these trucks are built around. Check these four things before you order, and the answer will be obvious.
| What to check | What this motor is | Result |
|---|---|---|
| Motor plate / can size | 3660 — 36 mm diameter, 60 mm long | Bolts to a standard 3660 plate |
| Pinion bore | 5 mm hardened steel shaft | A 5 mm bore pinion is required |
| Speed control plugs | 3 × 4 mm gold-plated bullets, pre-fitted | Plugs straight into 4 mm sockets |
| Power system | 2–3S LiPo (12.6V maximum) | On 3S, use a 100A or higher speed control |
| Vehicle class | 1/8 4X4 brushless street trucks and buggies running a 3660 mount | Direct replacement |
This motor, a cheap alternative, or your tired original.
Any 3660 motor with the right shaft and plugs will fit. What differs is what the numbers mean on the road, and whether the motor is still healthy after a season of street bashing. Here is the honest comparison.
| 3900Kv 4-pole (this motor) | Budget low-Kv motor | Your worn original | |
|---|---|---|---|
| Rpm per volt | 3900Kv | Often 2600–3300Kv | Was 3900Kv when new |
| Punch off the line | Strong, with 4-pole torque | Softer — fewer rpm per volt | Fading as bearings and rotor age |
| Top speed on 3S | Full, on the standard gearing | Lower unless you re-gear | Lower than it used to be |
| Heat and run time | Rated 45A continuous | Cheaper windings run hotter | Runs hot, drinks your pack dry |
| Bearings and shaft | Precision ball bearings, hardened 5 mm shaft | Mixed quality, often unbranded | Dry, noisy, with side play |
| Connectors | 4 mm gold-plated bullets, pre-fitted | May arrive bare, needing solder | Reusable — inspect them while you are in there |
| Who it suits | A direct replacement or an upgrade on any 3660 truck | Slower models and light use | Not a fix — it is the problem |
Every number, in one place.
Everything below is a measurable fact about the motor. If your truck runs a 3660 plate, a 5 mm pinion bore and 4 mm bullet sockets, this is a direct fit.
| Specification | Value |
|---|---|
| Motor type | Sensorless brushless, 4-pole |
| Can size | 3660 — 36 mm diameter × 60 mm long |
| Rpm per volt | 3900Kv |
| Rotor | Sintered 4-pole |
| Windings | High-purity copper |
| Housing | CNC machined aluminium |
| Bearings | Precision ball bearings, both ends |
| Output shaft | 5 mm hardened steel (5 mm bore pinion required) |
| Connectors | 3 × 4 mm gold-plated bullets, pre-fitted |
| Input voltage | 2–3S LiPo (12.6V maximum) |
| Maximum continuous current | 45A |
| Constant wattage | 500–749W |
| Mounting | Standard 3660 motor plate |
with 4 mm bullet connectors pre-fitted
A 5 mm bore pinion is required to fit it.
Look after it and it outlasts the truck.
Almost every motor that dies early died of the same three things: a bad gear mesh, dirt inside the can, or heat. Four habits cover all of them.
A pinion, a drop of bearing oil, a hex driver and a soft brush — everything this motor needs to stay healthy.
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