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...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...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...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...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...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...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...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...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
$88.95 -
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...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...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...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...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...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
$188.95Qty in Cart: 0Quantity:Price:$188.95Subtotal: -
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...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...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...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...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...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...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...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
