Dirt Bike Engine
Dirt Bike Engine Parts at JJ Motorsports
Discover a full range of dirt bike engine components for rebuilding or upgrading your performance from JJ Motorsports. From crankshafts to cylinder heads and piston kits, these precision-engineered components ensure reliable performance. For additional upgrades, check out our full selection of off-road dirt bike parts to keep your engine running at peak efficiency on the track or trails.
Shop trusted brands like Wiseco for forged piston kits and K&N for high-flow oil filters. Explore related categories such as Dirt Bike Air and Fuel for intake upgrades or Dirt Bike Exhaust for complete systems.
Browse our in-stock inventory below with same-day shipping and expert support. Questions? Contact us for fitment advice!
- Product
- Qty in Cart
- Quantity
- Price
- Subtotal
-
On Sale
PROX Valveshim - 10.00 x 2.90 - 5 pack 29.100290
PROX
MSRP: $9.95Now: $8.00Was: $9.95Valve shim replacement is a critical maintenance task that directly impacts engine performance, valve timing accuracy, and overall reliability. The PROX Valveshim offers a cost-effective alternative...09261011- SKU:
- 09261011
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- PRODUCT NAME:
- SHIM KIT
- TYPE:
- VALVE
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 2.90 MM
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- RIDING STYLE:
- OFF-ROAD
MSRP: $9.95Now: $8.00Was: $9.95 -
On Sale
PROX Valveshim - 10.00 x 2.95 - 5 pack 29.100295
PROX
MSRP: $9.95Now: $8.00Was: $9.95Valve shimming is critical to maintaining precise valve clearances, and worn or damaged shims directly compromise engine performance and longevity. The PROX Valveshim 10.00 x 2.95 delivers...09261012- SKU:
- 09261012
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- UNITS:
- 5 PACK
- RIDING STYLE:
- OFF-ROAD
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- TYPE:
- VALVE
- VALVE SHIM THICKNESS METRIC:
- 2.95 MM
MSRP: $9.95Now: $8.00Was: $9.95Qty in Cart: 0Quantity:Price:MSRP: $9.95Now: $8.00Was: $9.95Subtotal: -
On Sale
PROX Valveshim - 10.00 x 3.00 - 5 pack 29.100300
PROX
MSRP: $9.95Now: $8.00Was: $9.95Valve shims are critical wear items that directly impact your engine's valve clearance and overall performance. The PROX 10.00 x 3.00 Valveshim delivers precision engineering at a fraction of OEM...09261013- SKU:
- 09261013
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 3.00 MM
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- TYPE:
- VALVE
- RIDING STYLE:
- OFF-ROAD
MSRP: $9.95Now: $8.00Was: $9.95Qty in Cart: 0Quantity:Price:MSRP: $9.95Now: $8.00Was: $9.95Subtotal: -
On Sale
PROX Valveshim - 10.00 x 3.05 - 5 pack 29.100305
PROX
MSRP: $9.95Now: $8.00Was: $9.95Valve shim clearance directly impacts engine performance, longevity, and reliability—and worn or incorrect shims lead to costly valve damage and downtime. The PROX Valveshim offers...09261014- SKU:
- 09261014
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- PRODUCT NAME:
- SHIM KIT
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 3.05 MM
- RIDING STYLE:
- OFF-ROAD
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- TYPE:
- VALVE
MSRP: $9.95Now: $8.00Was: $9.95 -
On Sale
PROX Valveshim - 10.00 x 3.20 - 5 pack 29.100320
PROX
MSRP: $9.95Now: $8.00Was: $9.95Valve shim wear directly impacts engine timing and compression—critical factors in maintaining peak performance and reliability. PROX Valveshims deliver OEM-quality replacement at a fraction of the...09261017- SKU:
- 09261017
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- VALVE SHIM THICKNESS METRIC:
- 3.20 MM
- PRODUCT NAME:
- SHIM KIT
- UNITS:
- 5 PACK
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- TYPE:
- VALVE
MSRP: $9.95Now: $8.00Was: $9.95 -
On Sale
PROX Valve and Spring Kit 28.SIS1405-2
PROX
MSRP: $143.95Now: $119.00Was: $143.95If you're running your engine hard at high RPM, stock valve springs will eventually fail you—they simply aren't engineered for sustained extreme conditions. The PROX Valve and Spring Kit 28.SIS1405-2...09261021- SKU:
- 09261021
- Availability:
- Ships Same Business Day
- Weight:
- 0.34 LBS
- APPLICATION:
- INTAKE
- MATERIAL:
- STEEL
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
MSRP: $143.95Now: $119.00Was: $143.95 -
On Sale
PROX Valve and Spring Kit 28.SES2424-1
PROX
MSRP: $143.95Now: $119.00Was: $143.95If you're pushing your engine to the limit, your OEM valve train becomes the weak link. The PROX 28.SES2424-1 replaces stock valves and springs with nitrided steel components engineered to withstand...09261025- SKU:
- 09261025
- Availability:
- Ships Same Business Day
- Weight:
- 0.20 LBS
- TYPE:
- VALVE
- PRODUCT NAME:
- SPRING KIT
- APPLICATION:
- EXHAUST
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
MSRP: $143.95Now: $119.00Was: $143.95 -
On Sale
PROX Valve and Spring Kit 28.SIS4406-2
PROX
MSRP: $159.95Now: $136.00Was: $159.95If you're running your engine hard at sustained high RPM, your OEM valve train becomes the weak link. The PROX Valve and Spring Kit 28.SIS4406-2 upgrades both your valves and springs to handle the...09261031- SKU:
- 09261031
- Availability:
- Ships Same Business Day
- Weight:
- 0.36 LBS
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- APPLICATION:
- INTAKE
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
MSRP: $159.95Now: $136.00Was: $159.95 -
On Sale
PROX Valve and Spring Kit 28.SES4406-1
PROX
MSRP: $159.95Now: $136.00Was: $159.95If you're running your engine hard, OEM valves and springs will hold you back. The PROX 28.SES4406-1 Kit upgrades both your intake and exhaust valves to nitrided steel—engineered to withstand extreme...09261032- SKU:
- 09261032
- Availability:
- Ships Same Business Day
- Weight:
- 0.31 LBS
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- MATERIAL:
- STEEL
- APPLICATION:
- EXHAUST
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
MSRP: $159.95Now: $136.00Was: $159.95Qty in Cart: 0Quantity:Price:MSRP: $159.95Now: $136.00Was: $159.95Subtotal: -
On Sale
PROX Valve and Spring Kit 28.SIS4409-2
PROX
MSRP: $166.95Now: $136.00Was: $166.95If you're pushing your engine to its limits, OEM valves and springs won't cut it. The PROX Valve and Spring Kit 28.SIS4409-2 replaces stock components with nitrided steel valves and premium chrome...09261033- SKU:
- 09261033
- Availability:
- Ships Same Business Day
- Weight:
- 0.35 LBS
- UNITS:
- KIT
- APPLICATION:
- INTAKE
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
MSRP: $166.95Now: $136.00Was: $166.95 -
On Sale
PROX Valve and Spring Kit 28.SES4409-1
PROX
MSRP: $166.95Now: $136.00Was: $166.95If you're pushing your engine beyond stock parameters, OEM valves and springs will become your bottleneck. The PROX 28.SES4409-1 replaces factory components with nitrided steel valves and premium...09261034- SKU:
- 09261034
- Availability:
- Ships Same Business Day
- Weight:
- 0.30 LBS
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- APPLICATION:
- EXHAUST
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
MSRP: $166.95Now: $136.00Was: $166.95Qty in Cart: 0Quantity:Price:MSRP: $166.95Now: $136.00Was: $166.95Subtotal: -
On Sale
PROX Valve and Spring Kit 28.SIS3405-2
PROX
MSRP: $139.95Now: $119.00Was: $139.95If you're pushing your engine to high RPM territory, factory valve and spring assemblies become your limiting factor. The PROX 28.SIS3405-2 replaces weak OEM components with nitrided steel valves and...09261035- SKU:
- 09261035
- Availability:
- Ships Same Business Day
- Weight:
- 0.31 LBS
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- TYPE:
- VALVE
- APPLICATION:
- INTAKE
- PRODUCT NAME:
- SPRING KIT
MSRP: $139.95Now: $119.00Was: $139.95 -
On Sale
PROX Valve and Spring Kit 28.SES3405-1
PROX
MSRP: $139.95Now: $119.00Was: $139.95If you're pushing your engine to its limits, OEM valve and spring assemblies become your weakest link. The PROX 28.SES3405-1 replaces them with nitrided steel valves and premium chrome vanadium...09261036- SKU:
- 09261036
- Availability:
- Ships Same Business Day
- Weight:
- 0.21 LBS
- APPLICATION:
- EXHAUST
- TYPE:
- VALVE
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- MATERIAL:
- STEEL
- PRODUCT NAME:
- SPRING KIT
MSRP: $139.95Now: $119.00Was: $139.95Qty in Cart: 0Quantity:Price:MSRP: $139.95Now: $119.00Was: $139.95Subtotal: -
On Sale
PROX Valve and Spring Kit 28.SIS3407-2
PROX
MSRP: $139.95Now: $119.00Was: $139.95High-RPM engines demand valve components that can withstand extreme temperatures, pressure cycles, and mechanical stress without compromising reliability. The PROX Valve and Spring Kit 28.SIS3407-2...09261037- SKU:
- 09261037
- Availability:
- Ships Same Business Day
- Weight:
- 0.32 LBS
- PRODUCT NAME:
- SPRING KIT
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- TYPE:
- VALVE
- APPLICATION:
- INTAKE
- MATERIAL:
- STEEL
MSRP: $139.95Now: $119.00Was: $139.95Qty in Cart: 0Quantity:Price:MSRP: $139.95Now: $119.00Was: $139.95Subtotal: -
On Sale
PROX Valve and Spring Kit 28.SES3407-1
PROX
MSRP: $139.95Now: $119.00Was: $139.95If you're running your engine hard at high RPM, stock valve springs and valves become your bottleneck—they wear quickly under extreme conditions and can't handle sustained performance demands. The...09261038- SKU:
- 09261038
- Availability:
- Ships Same Business Day
- Weight:
- 0.22 LBS
- APPLICATION:
- EXHAUST
- TYPE:
- VALVE
- PRODUCT NAME:
- SPRING KIT
- UNITS:
- KIT
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
MSRP: $139.95Now: $119.00Was: $139.95Qty in Cart: 0Quantity:Price:MSRP: $139.95Now: $119.00Was: $139.95Subtotal: -
On Sale
PROX Valve and Spring Kit 28.SIS3408-2
PROX
MSRP: $143.95Now: $119.00Was: $143.95If you're pushing your engine beyond stock limits, OEM valves and springs become your weak link. The PROX 28.SIS3408-2 Valve and Spring Kit replaces those components with hardened steel valves and...09261039- SKU:
- 09261039
- Availability:
- Ships Same Business Day
- Weight:
- 0.32 LBS
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
- APPLICATION:
- INTAKE
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
MSRP: $143.95Now: $119.00Was: $143.95 -
On Sale
PROX Valve and Spring Kit 28.SES3408-1
PROX
MSRP: $143.95Now: $119.00Was: $143.95If you're running high-RPM applications or pushing your engine beyond stock limits, OEM valve and spring assemblies become a liability. The PROX 28.SES3408-1 replaces weak factory components with...09261040- SKU:
- 09261040
- Availability:
- Ships Same Business Day
- Weight:
- 0.26 LBS
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- TYPE:
- VALVE
- APPLICATION:
- EXHAUST
- PRODUCT NAME:
- SPRING KIT
MSRP: $143.95Now: $119.00Was: $143.95 -
On Sale
PROX Exhaust Valve 28.1070-1
PROX
MSRP: $25.95Now: $21.00Was: $25.95A precision exhaust valve is critical to maintaining proper scavenging, reducing backpressure, and maximizing power output in high-revving engines. The PROX 28.1070-1 delivers OEM-equivalent sealing...09260664- SKU:
- 09260664
- Availability:
- Ships Same Business Day
- Weight:
- 0.06 LBS
- APPLICATION:
- EXHAUST
- MATERIAL:
- STEEL
- PRODUCT NAME:
- VALVE
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- EACH
MSRP: $25.95Now: $21.00Was: $25.95 -
On Sale
PROX Intake Valve 28.1070-2
PROX
MSRP: $17.95Now: $13.00Was: $17.95A properly functioning intake valve is critical to your engine's breathing efficiency and combustion reliability. The PROX 28.1070-2 is precision-manufactured to OEM specifications, ensuring...09260665- SKU:
- 09260665
- Availability:
- Ships Same Business Day
- Weight:
- 0.06 LBS
- RIDING STYLE:
- OFF-ROAD
- APPLICATION:
- INTAKE
- MATERIAL:
- STEEL
- PRODUCT NAME:
- VALVE
- UNITS:
- EACH
MSRP: $17.95Now: $13.00Was: $17.95 -
On Sale
PROX Exhaust Valve 28.1226-1
PROX
MSRP: $30.95Now: $25.00Was: $30.95A precision exhaust valve is critical to maintaining proper engine breathing and combustion efficiency. The PROX 28.1226-1 delivers OEM-specification performance, ensuring reliable operation across...09260666- SKU:
- 09260666
- Availability:
- Ships Same Business Day
- Weight:
- 0.08 LBS
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- EACH
- MATERIAL:
- STEEL
- PRODUCT NAME:
- VALVE
- APPLICATION:
- EXHAUST
MSRP: $30.95Now: $25.00Was: $30.95
