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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On Sale
PROX Piston Kit 01.1408.050
PROX
MSRP: $185.95Now: $158.00Was: $185.95A piston kit is fundamental to engine reliability and performance—worn or damaged pistons compromise compression, increase blow-by, and accelerate engine wear. The PROX Piston Kit 01.1408.050 delivers OEM-equivalent engineering with Japanese...PX4042- SKU:
- PX4042
- Availability:
- Ships Same Business Day
- Weight:
- 1.26 LBS
- BORE SIZE METRIC:
- 89.50 MM
- ENGINE TYPE:
- 2-STROKE
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON SIZE METRIC:
- +0.50 MM
- RIDING STYLE:
- OFF-ROAD
- PISTON DIAMETER METRIC:
- 89.50 MM
MSRP: $185.95Now: $158.00Was: $185.95 -
On Sale
PROX Piston Kit 01.1408.100
PROX
MSRP: $199.95Now: $158.00Was: $199.95Worn or damaged pistons compromise combustion efficiency, reduce power output, and risk catastrophic engine failure. The PROX Piston Kit 01.1408.100 delivers OEM-specification performance with CNC-machined precision, restoring your engine to...PX4044- SKU:
- PX4044
- Availability:
- Ships Same Business Day
- Weight:
- 1.25 LBS
- BORE SIZE METRIC:
- 90.00 MM
- PISTON DIAMETER METRIC:
- 90.00 MM
- PRODUCT NAME:
- PISTON KIT
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PISTON SIZE METRIC:
- +1.00 MM
- UNITS:
- EACH
- ENGINE TYPE:
- 2-STROKE
- RIDING STYLE:
- OFF-ROAD
MSRP: $199.95Now: $158.00Was: $199.95 -
On Sale
PROX Piston Kit 01.1408.125
PROX
MSRP: $185.95Now: $158.00Was: $185.95When your engine demands reliability and precision, OEM-equivalent performance is non-negotiable. The PROX Piston Kit 01.1408.125 delivers exact fitment and durability through Japanese manufacturing expertise and high-silicon aluminum construction that...PX4045- SKU:
- PX4045
- Availability:
- Ships Same Business Day
- Weight:
- 1.35 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PRODUCT NAME:
- PISTON KIT
- BORE SIZE METRIC:
- 90.25 MM
- ENGINE TYPE:
- 2-STROKE
- PISTON DIAMETER METRIC:
- 90.25 MM
- PISTON SIZE IMPERIAL:
- +0.050'
- RIDING STYLE:
- OFF-ROAD
MSRP: $185.95Now: $158.00Was: $185.95 -
On Sale
PROX Piston Kit 01.1218.A1
PROX
MSRP: $132.95Now: $90.00Was: $132.95A piston kit is the heart of engine reliability and performance—without proper pistons, you're risking catastrophic failure under boost or high RPM. The PROX Piston Kit 01.1218.A1 delivers OEM-grade construction with precision engineering, ensuring your...PX4260A- SKU:
- PX4260A
- Availability:
- Ships Same Business Day
- Weight:
- 0.38 LBS
- RIDING STYLE:
- OFF-ROAD
- PISTON DIAMETER METRIC:
- 53.94 MM
- PRODUCT NAME:
- PISTON KIT
- BORE SIZE METRIC:
- 53.94 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
MSRP: $132.95Now: $90.00Was: $132.95 -
On Sale
PROX Piston Kit 01.1218.A2
PROX
MSRP: $132.95Now: $90.00Was: $132.95A worn or damaged piston directly compromises engine efficiency, compression, and longevity—especially under sustained high-RPM operation. The PROX Piston Kit 01.1218.A2 delivers OEM-equivalent performance with precision engineering, ensuring reliable...PX4260B- SKU:
- PX4260B
- Availability:
- Ships Same Business Day
- Weight:
- 0.38 LBS
- BORE SIZE METRIC:
- 53.95 MM
- PISTON DIAMETER METRIC:
- 53.95 MM
- PRODUCT NAME:
- PISTON KIT
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE A
- RIDING STYLE:
- OFF-ROAD
MSRP: $132.95Now: $90.00Was: $132.95 -
On Sale
PROX Piston Kit 01.1218.A4
PROX
MSRP: $132.95Now: $90.00Was: $132.95A piston kit is the backbone of engine reliability and performance—worn or damaged pistons lead to compression loss, increased blowby, and catastrophic engine failure. The PROX Piston Kit 01.1218.A4 delivers OEM-equivalent quality with precision...PX4260D- SKU:
- PX4260D
- Availability:
- Ships Same Business Day
- Weight:
- 0.40 LBS
- PISTON DIAMETER METRIC:
- 53.97 MM
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 53.97 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE A
MSRP: $132.95Now: $90.00Was: $132.95 -
On Sale
PROX Piston Kit 01.4121.A
PROX
MSRP: $99.95Now: $76.00Was: $99.95Factory pistons wear out or fail, leaving you with expensive downtime and compromised engine performance. The PROX Piston Kit 01.4121.A delivers OEM-equivalent quality at a fraction of the cost, engineered in Japan with the same exacting standards as...PX4281A- SKU:
- PX4281A
- Availability:
- Ships Same Business Day
- Weight:
- 0.42 LBS
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PRODUCT NAME:
- PISTON KIT
- PISTON DIAMETER METRIC:
- 48.45 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- BORE SIZE METRIC:
- 48.45 MM
- RIDING STYLE:
- OFF-ROAD
MSRP: $99.95Now: $76.00Was: $99.95 -
On Sale
PROX Ring Set 02.4121
PROX
MSRP: $24.95Now: $21.00Was: $24.95Piston ring wear directly impacts compression, blow-by, and fuel efficiency—making quality ring sets essential for maintaining peak engine performance. The PROX Ring Set 02.4121 delivers OEM-equivalent specifications with Japanese manufacturing...PX4281R- SKU:
- PX4281R
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- RIDING STYLE:
- OFF-ROAD
- PRODUCT NAME:
- PISTON RING
- UNITS:
- SET
MSRP: $24.95Now: $21.00Was: $24.95 -
On Sale
PROX Piston Kit 01.4216.B
PROX
MSRP: $121.95Now: $90.00Was: $121.95A worn or damaged piston compromises combustion efficiency, reduces power output, and can lead to catastrophic engine failure. The PROX Piston Kit 01.4216.B delivers OEM-level reliability with precision engineering, restoring your engine to factory...PX4296B- SKU:
- PX4296B
- Availability:
- Ships Same Business Day
- Weight:
- 0.38 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PISTON SIZE METRIC:
- STANDARD SIZE B
- UNITS:
- EACH
- PISTON DIAMETER METRIC:
- 53.96 MM
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 53.96 MM
- PRODUCT NAME:
- PISTON KIT
MSRP: $121.95Now: $90.00Was: $121.95 -
On Sale
PROX Piston Kit 01.4216.C
PROX
MSRP: $105.95Now: $90.00Was: $105.95When you're rebuilding an engine or replacing worn pistons, you need a drop-in solution that matches OEM performance without compromise. The PROX Piston Kit 01.4216.C delivers exactly that—factory-spec reliability with Japanese manufacturing precision...PX4296C- SKU:
- PX4296C
- Availability:
- Ships Same Business Day
- Weight:
- 0.38 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- EACH
- PISTON DIAMETER METRIC:
- 53.97 MM
- BORE SIZE METRIC:
- 53.97 MM
- PISTON SIZE METRIC:
- STANDARD SIZE C
- PRODUCT NAME:
- PISTON KIT
MSRP: $105.95Now: $90.00Was: $105.95 -
On Sale
PROX Piston Kit 01.4218.A
PROX
MSRP: $121.95Now: $90.00Was: $121.95A piston kit is the heart of your engine's combustion cycle—worn or damaged pistons directly compromise compression, power delivery, and engine longevity. The PROX Piston Kit 01.4218.A delivers OEM-equivalent performance with precision manufacturing that...PX4299A- SKU:
- PX4299A
- Availability:
- Ships Same Business Day
- Weight:
- 0.50 LBS
- BORE SIZE METRIC:
- 53.96 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PRODUCT NAME:
- PISTON KIT
- RIDING STYLE:
- OFF-ROAD
- PISTON DIAMETER METRIC:
- 53.96 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
MSRP: $121.95Now: $90.00Was: $121.95 -
On Sale
PROX Piston Kit 01.4218.C
PROX
MSRP: $121.95Now: $90.00Was: $121.95Your engine's power delivery and longevity depend on piston quality—and factory replacements often compromise on durability or precision. The PROX Piston Kit 01.4218.C delivers OEM-equivalent performance with Japanese manufacturing standards and...PX4299C- SKU:
- PX4299C
- Availability:
- Ships Same Business Day
- Weight:
- 0.42 LBS
- PRODUCT NAME:
- PISTON KIT
- BORE SIZE METRIC:
- 53.98 MM
- PISTON SIZE METRIC:
- STANDARD SIZE C
- RIDING STYLE:
- OFF-ROAD
- PISTON DIAMETER METRIC:
- 53.98 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
MSRP: $121.95Now: $90.00Was: $121.95 -
On Sale
PROX Piston Kit 01.4322.B
PROX
MSRP: $143.95Now: $119.00Was: $143.95A worn or damaged piston compromises combustion efficiency, power delivery, and engine longevity. The PROX Piston Kit 01.4322.B restores OEM-level performance with precision-engineered components manufactured to exacting tolerances in Japan. This...PX4308B- SKU:
- PX4308B
- Availability:
- Ships Same Business Day
- Weight:
- 0.75 LBS
- PISTON DIAMETER METRIC:
- 66.35 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- BORE SIZE METRIC:
- 66.35 MM
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE B
- RIDING STYLE:
- OFF-ROAD
MSRP: $143.95Now: $119.00Was: $143.95 -
On Sale
PROX Piston Kit 01.4322.C
PROX
MSRP: $143.95Now: $119.00Was: $143.95A piston kit is the heart of your engine's combustion chamber—when yours shows wear, blow-by, or loss of compression, replacement becomes non-negotiable for reliable performance. The PROX Piston Kit 01.4322.C delivers OEM-equivalent engineering with...PX4308C- SKU:
- PX4308C
- Availability:
- Ships Same Business Day
- Weight:
- 0.75 LBS
- PISTON DIAMETER METRIC:
- 66.36 MM
- PISTON SIZE METRIC:
- STANDARD SIZE C
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- BORE SIZE METRIC:
- 66.36 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- RIDING STYLE:
- OFF-ROAD
MSRP: $143.95Now: $119.00Was: $143.95 -
On Sale
PROX Piston Kit 01.4285.A
PROX
MSRP: $132.95Now: $110.00Was: $132.95When your engine's factory pistons show wear or you're rebuilding after high-mileage use, settling for inferior replacements compromises reliability and performance. The PROX Piston Kit 01.4285.A delivers OEM-equivalent durability with precision...PX4310A- SKU:
- PX4310A
- Availability:
- Ships Same Business Day
- Weight:
- 0.55 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PISTON DIAMETER METRIC:
- 65.94 MM
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 65.94 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PRODUCT NAME:
- PISTON KIT
MSRP: $132.95Now: $110.00Was: $132.95 -
On Sale
PROX Piston Kit 01.4285.B
PROX
MSRP: $132.95Now: $110.00Was: $132.95When your engine's internals are worn or damaged, a quality piston kit is non-negotiable for restoring reliable power and compression. The PROX Piston Kit 01.4285.B delivers OEM-grade performance without the OEM price tag, engineered to exact factory...PX4310B- SKU:
- PX4310B
- Availability:
- Ships Same Business Day
- Weight:
- 0.60 LBS
- PISTON DIAMETER METRIC:
- 65.95 MM
- RIDING STYLE:
- OFF-ROAD
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE B
- BORE SIZE METRIC:
- 65.95 MM
- PRODUCT NAME:
- PISTON KIT
MSRP: $132.95Now: $110.00Was: $132.95 -
On Sale
PROX Piston Kit 01.4285.C
PROX
MSRP: $132.95Now: $110.00Was: $132.95A piston kit is fundamental to engine reliability and performance—worn or damaged pistons compromise combustion efficiency, increase blow-by, and risk catastrophic engine failure. The PROX Piston Kit 01.4285.C delivers OEM-equivalent quality at a...PX4310C- SKU:
- PX4310C
- Availability:
- Ships Same Business Day
- Weight:
- 0.65 LBS
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- EACH
- PRODUCT NAME:
- PISTON KIT
- PISTON DIAMETER METRIC:
- 65.96 MM
- BORE SIZE METRIC:
- 65.96 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PISTON SIZE METRIC:
- STANDARD SIZE C
MSRP: $132.95Now: $110.00Was: $132.95 -
On Sale
PROX Piston Kit 01.1315.A
PROX
MSRP: $139.95Now: $119.00Was: $139.95A piston kit is your foundation for reliable engine performance and longevity. The PROX Piston Kit 01.1315.A delivers OEM-equivalent quality with precision engineering that ensures proper ring sealing, reduced blowby, and consistent combustion across the...PX4420A- SKU:
- PX4420A
- Availability:
- Ships Same Business Day
- Weight:
- 0.63 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- BORE SIZE METRIC:
- 66.34 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- RIDING STYLE:
- OFF-ROAD
- PISTON DIAMETER METRIC:
- 66.34 MM
- PRODUCT NAME:
- PISTON KIT
MSRP: $139.95Now: $119.00Was: $139.95 -
On Sale
PROX Ring Set 02.1315
PROX
MSRP: $49.95Now: $42.00Was: $49.95Worn piston rings directly compromise combustion efficiency, oil consumption, and overall engine reliability—making a quality replacement essential for consistent performance. The PROX Ring Set 02.1315 delivers OEM-grade engineering with the precision...PX4420R- SKU:
- PX4420R
- Availability:
- Ships Same Business Day
- Weight:
- 0.05 LBS
- PRODUCT NAME:
- PISTON RING
- UNITS:
- SET
- RIDING STYLE:
- OFF-ROAD
- PISTON MATERIAL:
- ALUMINUM ALLOY
MSRP: $49.95Now: $42.00Was: $49.95 -
On Sale
PROX Piston Kit 01.1320.A
PROX
MSRP: $143.95Now: $119.00Was: $143.95Your engine's performance and longevity depend on pistons that can withstand extreme temperatures, pressures, and RPMs without compromise. The PROX Piston Kit 01.1320.A is engineered as a direct OEM replacement, delivering the precision fit and...PX4430A- SKU:
- PX4430A
- Availability:
- Ships Same Business Day
- Weight:
- 0.63 LBS
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 66.34 MM
- PISTON DIAMETER METRIC:
- 66.34 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PRODUCT NAME:
- PISTON KIT
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
MSRP: $143.95Now: $119.00Was: $143.95
