The Heavy Hitter 520 Primary Drive Conversion OEM/EBMX Ultra Motors is a 520 chain primary drive for the Sur Ron Ultra Bee with the OEM or EBMX XUB-80 motor, made by Heavy Hitter and sold here at GritShift. It pairs a hard-anodized 7075-T6 28-tooth sprocket with a heat-treated steel front sprocket, weighs 2.4 lb, and torques to 10 Nm throughout.
Specs verified September 2026 against the live GritShift product page and the Heavy Hitter tech sheet.
Specifications
| Type | 520 primary chain drive conversion for the Sur Ron Ultra Bee |
|---|---|
| Rear sprocket | 28-tooth, hard-anodized 7075-T6 billet aluminum, dished design, on a primary hub |
| Front sprocket | 12-tooth Heat-treated, counter-cut steel |
| Chain | Japanese-made 520 non-O-ring chain with master link |
| Weight | 2.4 lb |
| Hardware | Included: 6 x stainless steel countersunk hex head screws M6x18, 6 x stainless steel countersunk hex head screws M6x16, 6 x stainless steel M6 flanged nuts, 1 x spacing shim |
| Torque | M6x16 screws 10 Nm (7 ft-lb); M6x18 screws 10 Nm (7 ft-lb); M6 flanged nuts 10 Nm (7 ft-lb) |
| Tools | 4 mm Allen wrench, 10 mm socket or wrench, torque wrench, medium-strength (blue) thread locker |
| Spacer position | Between motor and sprocket for the OEM and V2 EBMX XUB-80 motors; outside the sprocket for the V1 EBMX XUB-80 only |
| Dampers | None; no rubber dampers |
| Gear ratio | Maintains the OEM gear ratio and motor alignment |
| Tech sheet | Heavy Hitter 520 Primary Drive Conversion assembly guide (PDF) |
What bikes does the Heavy Hitter 520 primary drive fit?
- Sur Ron Ultra Bee with the OEM motor
- Sur Ron Ultra Bee with the EBMX V1 or V2 XUB-80 motor
Why run a 520 chain primary on the Ultra Bee?
Heavy Hitter describes this as the lightest 520 chain drive kit on the market for the Ultra Bee, built for riders who want maximum performance with minimum rotational mass. With no rubber dampers there is no efficiency loss, no additional heat buildup and no debris shelf for chain links to pack into, and the kit maintains the OEM gear ratio and motor alignment. It has been run on the EBMX FIM E-Xplorer race team bikes ridden by Jack Field and Jess Gardiner. Heavy Hitter notes that the kit is loud compared to a belt, though no louder than any other chain kit.
What is in the box?
- 1 x primary hub
- 1 x Ultra Bee 28-tooth rear chain sprocket
- 1 x Ultra Bee 12-tooth front chain sprocket
- 1 x Ultra Bee 520 primary chain front sprocket
- 1 x spacing shim
- 6 x stainless steel countersunk hex head screws M6x18
- 6 x stainless steel countersunk hex head screws M6x16
- 6 x stainless steel M6 flanged nuts
- Japanese-made 520 non-O-ring chain with master link
Where does the spacer go on an EBMX motor?
It depends on the motor generation. For the OEM motor and the V2 EBMX XUB-80, the spacer sits between the motor and the front sprocket. For the V1 EBMX XUB-80 only, the sprocket goes against the motor and the spacer sits outside it. In both cases the chamfer cut-out on the sprocket faces out. Heavy Hitter adds that some aftermarket motors have an offset difference, so check chain alignment before riding; most aftermarket motors include shims for proper installation. The diagrams are on the assembly guide (PDF).
How do I torque the 520 primary drive?
Every fastener in the kit torques to 10 Nm (7 ft-lb): the M6x16 and M6x18 countersunk screws and the M6 flanged nuts. Use a 4 mm Allen wrench, a 10 mm socket or wrench and a torque wrench, and apply medium-strength blue thread locker. The product page repeats the point: ensure all hardware is tightened and thread locker is applied. The exclusive dished sprocket design gives proper clearance, and the master link chain keeps swaps and maintenance simple.
Where can I buy the Heavy Hitter 520 Primary Drive Conversion OEM/EBMX Ultra Motors?
Right here. We sell the Heavy Hitter 520 Primary Drive Conversion OEM/EBMX Ultra Motors at GritShift.
