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 to OEM shims without compromising the precision and...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 OEM-equivalent precision at a fraction of the cost, making it the...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: $9.95 -
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 replacement costs, making routine maintenance accessible...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: $9.95 -
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 precision-engineered replacement at a fraction of OEM costs, with...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 cost, using precision heat-treatment and CNC machining...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 replaces worn or inadequate OEM components with...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 extreme RPM and combustion pressures without...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 demands of extreme conditions—reducing wear, improving...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 heat, pressure, and RPM cycles without the wear that...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 vanadium springs engineered to handle the demands of...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 chrome vanadium springs engineered to handle extreme RPMs...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: $166.95 -
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 premium chrome vanadium springs engineered to handle...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 springs engineered to handle sustained high-RPM operation...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: $139.95 -
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 replaces factory valves and springs with nitrided steel...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 PROX Valve and Spring Kit replaces those weak points with...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 premium chrome vanadium springs engineered to handle...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 nitrided steel valves and premium chrome vanadium springs...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 and durability, making it an essential replacement for...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 consistent sealing and optimal airflow into your combustion...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 demanding driving conditions. Whether you're rebuilding...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
