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 Top End Gasket Set - Beta 35.7219
PROX
MSRP: $54.55Now: $42.00Was: $54.55A top-end rebuild demands precision sealing—any leak compromises compression, performance, and reliability. The PROX Top End Gasket Set delivers OEM-equivalent quality through factory-controlled manufacturing, ensuring consistent bore sealing across...09347780- SKU:
- 09347780
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $54.55Now: $42.00Was: $54.55 -
On Sale
PROX Top End Gasket Set - Beta 35.7220
PROX
MSRP: $54.55Now: $42.00Was: $54.55A top-end rebuild demands gasket integrity that won't compromise your engine's sealing surfaces or performance gains. The PROX Top End Gasket Set delivers OEM-equivalent quality without the premium price, engineered to ProX specifications for reliable...09347781- SKU:
- 09347781
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $54.55Now: $42.00Was: $54.55 -
On Sale
PROX Top End Gasket Set - Beta 35.7313
PROX
MSRP: $66.10Now: $51.00Was: $66.10A compromised top-end gasket set will leak compression, rob horsepower, and leave you stranded. The PROX 35.7313 delivers the complete gasket set you need for a proper rebuild, engineered to seal reliably under sustained high heat and cylinder pressure...09347782- SKU:
- 09347782
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $66.10Now: $51.00Was: $66.10 -
On Sale
PROX Top End Gasket Set - Sherco 35.7314
PROX
MSRP: $93.40Now: $72.00Was: $93.40A leaking or worn top-end gasket set will compromise your Sherco's compression, throttle response, and overall reliability—especially critical if you're running lean jetting or pushing higher RPMs. This ProX gasket set delivers factory-spec sealing...09347783- SKU:
- 09347783
- Availability:
- Ships Same Business Day
- Weight:
- 0.10 LBS
MSRP: $93.40Now: $72.00Was: $93.40 -
On Sale
PROX Top End Gasket Set - Beta 35.7322
PROX
MSRP: $66.10Now: $51.00Was: $66.10A top-end rebuild demands precision sealing—any leak or gasket failure can compromise compression, reduce power output, and lead to costly engine damage. The PROX Top End Gasket Set delivers OEM-level quality at a fraction of dealership pricing,...09347784- SKU:
- 09347784
- Availability:
- Ships Same Business Day
- Weight:
- 0.22 LBS
MSRP: $66.10Now: $51.00Was: $66.10 -
On Sale
PROX Top End Gasket Set - Beta 35.7323
PROX
MSRP: $66.10Now: $51.00Was: $66.10A top-end rebuild demands precision-fit gaskets that seal reliably under extreme combustion pressures and temperature cycling. The PROX Top End Gasket Set delivers factory-spec tolerances and material consistency across all critical sealing surfaces,...09347785- SKU:
- 09347785
- Availability:
- Ships Same Business Day
- Weight:
- 0.22 LBS
MSRP: $66.10Now: $51.00Was: $66.10 -
On Sale
PROX Top End Gasket Set - Sherco 35.7324
PROX
MSRP: $104.95Now: $81.00Was: $104.95A degraded top-end gasket set compromises engine sealing, reducing compression and inviting coolant or oil seepage that can sideline your Sherco mid-season. The PROX 35.7324 delivers OEM-grade sealing surfaces with materials engineered to handle...09347786- SKU:
- 09347786
- Availability:
- Ships Same Business Day
- Weight:
- 0.18 LBS
MSRP: $104.95Now: $81.00Was: $104.95 -
On Sale
PROX Top End Gasket Set - Beta 35.7332
PROX
MSRP: $66.10Now: $51.00Was: $66.10A top-end rebuild demands precision sealing—any leak compromises compression, power delivery, and engine longevity. The PROX Top End Gasket Set delivers OEM-quality sealing with factory specifications that eliminate guesswork during your rebuild. Whether...09347787- SKU:
- 09347787
- Availability:
- Ships Same Business Day
- Weight:
- 0.22 LBS
MSRP: $66.10Now: $51.00Was: $66.10 -
On Sale
PROX Top End Gasket Set - Beta 35.7351
PROX
MSRP: $137.50Now: $106.00Was: $137.50A degraded top-end gasket set compromises compression, invites oil leakage, and forces you into unnecessary downtime. The PROX 35.7351 delivers OEM-equivalent sealing across all critical junctions, restoring your engine's integrity and allowing you to...09347788- SKU:
- 09347788
- Availability:
- Ships Same Business Day
- Weight:
- 0.25 LBS
MSRP: $137.50Now: $106.00Was: $137.50 -
On Sale
PROX Top End Gasket Set - Beta 35.7360
PROX
MSRP: $137.50Now: $106.00Was: $137.50A top-end rebuild demands precision—and this gasket set delivers the sealing integrity your engine needs to perform reliably under race conditions or high-demand use. ProX engineered each gasket to withstand extreme temperatures while maintaining a...09347789- SKU:
- 09347789
- Availability:
- Ships Same Business Day
- Weight:
- 0.20 LBS
MSRP: $137.50Now: $106.00Was: $137.50 -
On Sale
PROX Top End Gasket Set - Beta 35.7416
PROX
MSRP: $137.50Now: $106.00Was: $137.50A top-end rebuild demands precision sealing—any compromise risks compression loss, coolant seepage, and catastrophic engine failure. The PROX Top End Gasket Set (35.7416) delivers OEM-quality construction with materials engineered to handle sustained...09347790- SKU:
- 09347790
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $137.50Now: $106.00Was: $137.50 -
On Sale
PROX Top End Gasket Set - Beta 35.7420
PROX
MSRP: $137.50Now: $106.00Was: $137.50A compromised top-end gasket set will cost you power, reliability, and eventually, engine damage. The PROX Top End Gasket Set (35.7420) delivers the precision sealing your Beta engine needs to prevent oil and coolant leaks while maintaining proper...09347791- SKU:
- 09347791
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $137.50Now: $106.00Was: $137.50 -
On Sale
PROX Top End Gasket Set - Beta 35.7426
PROX
MSRP: $137.50Now: $106.00Was: $137.50A worn top-end gasket set compromises combustion sealing, leading to compression loss and decreased power output. The PROX 35.7426 restores proper sealing integrity across your top-end, ensuring consistent cylinder pressure and reliable performance...09347792- SKU:
- 09347792
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $137.50Now: $106.00Was: $137.50 -
On Sale
PROX Top End Gasket Set - Beta 35.7430
PROX
MSRP: $137.50Now: $106.00Was: $137.50When you're rebuilding your Beta's top end, a failed gasket means catastrophic oil loss, coolant leaks, and potential engine damage—none of which you can afford mid-season. The PROX Top End Gasket Set delivers precision-manufactured sealing surfaces...09347793- SKU:
- 09347793
- Availability:
- Ships Same Business Day
- Weight:
- 0.15 LBS
MSRP: $137.50Now: $106.00Was: $137.50 -
On Sale
PROX Piston Kit - 78.97 mm - Honda CRF250R/CRF250RX 01.1350.A
PROX
MSRP: $188.95Now: $158.00Was: $188.95A worn or damaged piston compromises engine compression, throttle response, and overall reliability—especially critical in a high-revving 250cc four-stroke. The PROX Piston Kit delivers OEM-equivalent performance with precision CNC machining and...09106779- SKU:
- 09106779
- Availability:
- Ships Same Business Day
- Weight:
- 0.53 LBS
MSRP: $188.95Now: $158.00Was: $188.95Qty in Cart: 0Quantity:Price:MSRP: $188.95Now: $158.00Was: $188.95Subtotal: -
On Sale
PROX Piston Kit - 53.95 mm - Yamaha YZ125/YZ125X 01.2232.A
PROX
MSRP: $121.95Now: $90.00Was: $121.95A worn or damaged piston directly compromises your YZ125/YZ125X's power delivery, compression, and engine reliability. The PROX 53.95 mm Piston Kit restores your engine to OEM performance specifications with precision-manufactured components engineered...09106780- SKU:
- 09106780
- Availability:
- Ships Same Business Day
- Weight:
- 0.45 LBS
MSRP: $121.95Now: $90.00Was: $121.95Qty in Cart: 0Quantity:Price:MSRP: $121.95Now: $90.00Was: $121.95Subtotal: -
On Sale
PROX Piston Kit - 96.95 mm - Yamaha WR450F/YZ450F/YZ450FX 01.2448.A
PROX
MSRP: $210.95Now: $167.00Was: $210.95When your Yamaha WR450F or YZ450F demands more from its engine, a quality piston kit is non-negotiable. This PROX kit delivers precision-machined components engineered to exact OEM specifications, restoring lost compression and power while maximizing...09106781- SKU:
- 09106781
- Availability:
- Ships Same Business Day
- Weight:
- 0.55 LBS
MSRP: $210.95Now: $167.00Was: $210.95Qty in Cart: 0Quantity:Price:MSRP: $210.95Now: $167.00Was: $210.95Subtotal: -
On Sale
PROX Piston Kit - 96.95 mm - Yamaha WR450F/YZ450F/YZ450FX 01.2450.A
PROX
MSRP: $221.95Now: $183.00Was: $221.95A piston kit is one of the most critical components in your engine's combustion chamber—it directly impacts power delivery, reliability, and longevity. The PROX 96.95 mm kit for your WR450F/YZ450F/YZ450FX delivers precision-engineered components machined...09106782- SKU:
- 09106782
- Availability:
- Ships Same Business Day
- Weight:
- 1.00 LBS
MSRP: $221.95Now: $183.00Was: $221.95 -
On Sale
PROX Piston Kit - 96.95 mm - Yamaha WR450F/YZ450F/YZ450FX 01.2453.A
PROX
MSRP: $221.95Now: $183.00Was: $221.95A worn or damaged piston directly impacts your WR450F or YZ450F's compression ratio, throttle response, and overall reliability—especially under high-RPM racing conditions. This PROX piston kit restores OEM specifications with precision-machined...09106783- SKU:
- 09106783
- Availability:
- Ships Same Business Day
- Weight:
- 0.93 LBS
MSRP: $221.95Now: $183.00Was: $221.95 -
On Sale
PROX Piston Kit - 77.96 mm - Kawasaki KX250/KX250X 01.4353.A
PROX
MSRP: $188.95Now: $158.00Was: $188.95The piston is the heart of your engine's combustion cycle—wear, scoring, or improper tolerances kill power and reliability. This PROX kit delivers OEM-equivalent precision for the Kawasaki KX250/KX250X, ensuring proper ring sealing, minimal blowby, and...09106787- SKU:
- 09106787
- Availability:
- Ships Same Business Day
- Weight:
- 0.50 LBS
MSRP: $188.95Now: $158.00Was: $188.95
