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
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PROX Valve and Spring Kit 28.SES6327-1
PROX
$155.95OEM valve springs lose their tension under sustained high-RPM operation, leading to valve float and catastrophic engine failure. The PROX Valve and Spring Kit 28.SES6327-1 replaces those compromised components with nitrided steel valves and premium...09261429- SKU:
- 09261429
- Availability:
- Ships Same Business Day
- Weight:
- 0.26 LBS
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- APPLICATION:
- EXHAUST
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
$155.95 -
PROX Valve and Spring Kit 28.SES6329-1
PROX
$155.95If you're running your engine hard, OEM valves and springs will hold you back. The PROX 28.SES6329-1 Kit replaces weak factory components with nitrided steel valves and premium chrome vanadium springs engineered to handle sustained high-RPM abuse without...09261430- SKU:
- 09261430
- Availability:
- Ships Same Business Day
- Weight:
- 0.24 LBS
- APPLICATION:
- EXHAUST
- TYPE:
- VALVE
- PRODUCT NAME:
- SPRING KIT
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- MATERIAL:
- STEEL
$155.95 -
PROX Valve and Spring Kit 28.SIS1409-2
PROX
$139.95High-RPM applications demand valve components that can withstand extreme heat, pressure, and cycling without degradation—stock valves simply won't cut it. The PROX Valve and Spring Kit upgrades your engine with nitrided steel valves and premium chrome...09261431- SKU:
- 09261431
- Availability:
- Ships Same Business Day
- Weight:
- 0.31 LBS
- APPLICATION:
- INTAKE
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
$139.95Qty in Cart: 0Quantity:Price:$139.95Subtotal: -
PROX Valve and Spring Kit 28.SIS2440-2
PROX
$139.95If you're pushing your engine to the limit, your OEM valves and springs won't keep pace. The PROX 28.SIS2440-2 Kit replaces worn or inadequate factory components with nitrided steel valves and premium chrome vanadium springs engineered to handle extreme...09261432- SKU:
- 09261432
- Availability:
- Ships Same Business Day
- Weight:
- 0.34 LBS
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- APPLICATION:
- INTAKE
$139.95Qty in Cart: 0Quantity:Price:$139.95Subtotal: -
PROX Valve and Spring Kit 28.SIS6327-2
PROX
$149.95If you're running high-RPM applications or building a race engine, OEM valve assemblies won't cut it. The PROX Valve and Spring Kit 28.SIS6327-2 replaces stock valves and springs with nitrided steel construction and premium chrome vanadium springs...09261435- SKU:
- 09261435
- Availability:
- Ships Same Business Day
- Weight:
- 0.27 LBS
- MATERIAL:
- STEEL
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- APPLICATION:
- INTAKE
- PRODUCT NAME:
- SPRING KIT
- TYPE:
- VALVE
$149.95Qty in Cart: 0Quantity:Price:$149.95Subtotal: -
PROX Piston Kit 01.1113.B
PROX
$99.95A piston kit is critical to engine reliability and performance—worn or damaged pistons compromise compression, increase blow-by, and accelerate engine degradation. The PROX Piston Kit 01.1113.B delivers OEM-equivalent durability with precision...09100020- SKU:
- 09100020
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- PRODUCT NAME:
- PISTON KIT
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 47.45 MM
- ENGINE TYPE:
- 2-STROKE
- PISTON SIZE METRIC:
- STANDARD SIZE B
- PISTON DIAMETER METRIC:
- 47.45 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
$99.95 -
PROX Piston Kit 01.1113.C
PROX
$99.95Whether you're rebuilding a tired engine or replacing worn pistons, the PROX Piston Kit 01.1113.C delivers the precision and reliability that professional rebuilds demand. Engineered as a direct OEM replacement with Japanese manufacturing standards, this...09100021- SKU:
- 09100021
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- PISTON DIAMETER METRIC:
- 47.46 MM
- PISTON SIZE METRIC:
- STANDARD SIZE C
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 47.46 MM
- ENGINE TYPE:
- 2-STROKE
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PRODUCT NAME:
- PISTON KIT
$99.95 -
PROX Piston Kit 01.4022.A
PROX
$88.95Worn or damaged pistons compromise combustion efficiency, reduce power output, and risk catastrophic engine failure. The PROX Piston Kit 01.4022.A delivers OEM-equivalent performance with precision engineering, ensuring reliable ring sealing, proper bore...09100022- SKU:
- 09100022
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- BORE SIZE METRIC:
- 44.45 MM
- PISTON DIAMETER METRIC:
- 42.96 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE A
- RIDING STYLE:
- OFF-ROAD
$88.95Qty in Cart: 0Quantity:Price:$88.95Subtotal: -
PROX Piston Kit 01.4022.B
PROX
$88.95When your engine demands reliability under extreme conditions, OEM-spec pistons are non-negotiable. The PROX Piston Kit 01.4022.B delivers factory-quality performance with the precision tolerances required for high-RPM stability and consistent...09100023- SKU:
- 09100023
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- BORE SIZE METRIC:
- 44.46 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON DIAMETER METRIC:
- 44.46 MM
- PISTON SIZE METRIC:
- STANDARD SIZE B
- RIDING STYLE:
- OFF-ROAD
$88.95 -
PROX Piston Kit 01.4223.B
PROX
$105.95A piston kit is fundamental to engine longevity and performance—worn or damaged pistons compromise compression, increase blow-by, and accelerate engine wear. The PROX Piston Kit 01.4223.B delivers OEM-equivalent quality without the OEM price tag, using...09100025- SKU:
- 09100025
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PISTON DIAMETER METRIC:
- 53.96 MM
- RIDING STYLE:
- OFF-ROAD
- ENGINE TYPE:
- 2-STROKE
- PISTON SIZE METRIC:
- STANDARD SIZE B
- UNITS:
- EACH
- BORE SIZE METRIC:
- 53.96 MM
- PRODUCT NAME:
- PISTON KIT
$105.95Qty in Cart: 0Quantity:Price:$105.95Subtotal: -
PROX Piston Kit 01.4223.C
PROX
$101.95Worn or damaged pistons directly compromise engine reliability, power delivery, and fuel efficiency—making a quality replacement essential for any serious rebuild or refresh. The PROX Piston Kit 01.4223.C delivers OEM-specification performance with...09100026- SKU:
- 09100026
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- BORE SIZE METRIC:
- 53.97 MM
- PISTON SIZE METRIC:
- STANDARD SIZE C
- ENGINE TYPE:
- 2-STROKE
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PISTON DIAMETER METRIC:
- 53.97 MM
- RIDING STYLE:
- OFF-ROAD
- PRODUCT NAME:
- PISTON KIT
$101.95Qty in Cart: 0Quantity:Price:$101.95Subtotal: -
PROX Piston Kit 01.2406.A
PROX
$179.95A piston kit is critical to engine reliability and performance—worn or damaged pistons compromise compression, fuel efficiency, and power delivery. The PROX Piston Kit 01.2406.A delivers OEM-equivalent quality with precision manufacturing, ensuring your...09100027- SKU:
- 09100027
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- PISTON DIAMETER METRIC:
- 76.95 MM
- BORE SIZE METRIC:
- 76.95 MM
- ENGINE TYPE:
- 4-STROKE
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE A
- RIDING STYLE:
- OFF-ROAD
$179.95Qty in Cart: 0Quantity:Price:$179.95Subtotal: -
PROX Piston Kit 01.2406.B
PROX
$188.95A worn or damaged piston compromises engine compression, efficiency, and reliability—especially under boost or sustained high RPM. The PROX Piston Kit 01.2406.B delivers OEM-equivalent performance with precision manufacturing that ensures proper ring...09100028- SKU:
- 09100028
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- BORE SIZE METRIC:
- 76.96 MM
- ENGINE TYPE:
- 4-STROKE
- PISTON DIAMETER METRIC:
- 76.96 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE B
- RIDING STYLE:
- OFF-ROAD
$188.95 -
PROX Piston Kit 01.2427.A
PROX
$205.95A worn or damaged piston kit severely limits engine performance and can lead to catastrophic failure if not addressed promptly. The PROX Piston Kit 01.2427.A restores your engine to OEM specifications with precision-engineered components manufactured to...09100031- SKU:
- 09100031
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
- BORE SIZE METRIC:
- 94.95 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- RIDING STYLE:
- OFF-ROAD
- ENGINE TYPE:
- 4-STROKE
- PISTON DIAMETER METRIC:
- 94.95 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
$205.95 -
PROX Piston Kit - KDX200 '86-'06 01.4285.D
PROX
$132.95A worn or damaged piston directly kills engine performance and reliability. The PROX Piston Kit restores your KDX200 to OEM specifications with Japanese-manufactured precision, ensuring consistent compression, reduced blow-by, and extended engine life...09101453- SKU:
- 09101453
- Availability:
- Ships Same Business Day
- Weight:
- 0.50 LBS
- PISTON DIAMETER METRIC:
- 65.97 MM
- PRODUCT NAME:
- PISTON KIT
- PISTON MATERIAL:
- ALUMINUM
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- KIT
- ENGINE TYPE:
- 2-STROKE
- SKIRT COATING:
- MOLY COATED
$132.95 -
PROX Piston Kit 01.4409.A
PROX
$189.95If your engine is showing signs of wear—loss of compression, increased blow-by, or declining power output—a quality piston kit is essential to restore performance and reliability. The PROX Piston Kit 01.4409.A delivers OEM-level engineering with...09101465- SKU:
- 09101465
- Availability:
- Ships Same Business Day
- Weight:
- 0.82 LBS
- RIDING STYLE:
- OFF-ROAD
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- BORE SIZE METRIC:
- 95.97 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PISTON DIAMETER METRIC:
- 95.97 MM
$189.95Qty in Cart: 0Quantity:Price:$189.95Subtotal: -
PROX Piston Kit 01.4409.B
PROX
$210.95Pistons are the heart of any engine, and worn or damaged units directly compromise compression, power delivery, and reliability. The PROX Piston Kit 01.4409.B delivers OEM-equivalent performance with precision engineering, making it the ideal choice for...09101466- SKU:
- 09101466
- Availability:
- Ships Same Business Day
- Weight:
- 0.85 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PISTON SIZE METRIC:
- STANDARD SIZE B
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- EACH
- BORE SIZE METRIC:
- 95.98 MM
- PRODUCT NAME:
- PISTON KIT
- PISTON DIAMETER METRIC:
- 95.98 MM
$210.95 -
PROX Top End Gasket Set - Yamaha 35.2214
PROX
$25.95A quality top-end gasket set is essential for maintaining compression integrity and preventing oil seepage across your cylinder head. PROX delivers OEM-equivalent sealing performance with precision-cut gaskets that ensure reliable engine operation...09345693- SKU:
- 09345693
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
- PRODUCT NAME:
- GASKET SET
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- SET
- TYPE:
- TOP END
$25.95Qty in Cart: 0Quantity:Price:$25.95Subtotal: -
PROX Top End Gasket Set - Yamaha 35.2218
PROX
$25.95A quality top-end gasket set is non-negotiable for maintaining compression integrity and preventing oil seepage in your Yamaha engine. Whether you're rebuilding after a refresh or replacing worn seals, the PROX 35.2218 ensures proper sealing across all...09345694- SKU:
- 09345694
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
- RIDING STYLE:
- OFF-ROAD
- PRODUCT NAME:
- GASKET SET
- TYPE:
- TOP END
- UNITS:
- SET
$25.95 -
PROX Top End Gasket Set - Yamaha 35.2222
PROX
$25.95A quality top-end gasket set is non-negotiable for engine reliability and longevity. Whether you're rebuilding after a high-mileage service or preparing for competition, PROX's precision-engineered gaskets seal critical surfaces and prevent oil weeping,...09345695- SKU:
- 09345695
- Availability:
- Ships Same Business Day
- Weight:
- 0.10 LBS
- UNITS:
- SET
- PRODUCT NAME:
- GASKET SET
- TYPE:
- TOP END
- RIDING STYLE:
- OFF-ROAD
$25.95
