Rebuilding RZR Engines the Easy Way: Polaris 800 Rebuild Kits

June 22, 2022 / by Kevin Bailey

ProX has expanded their ATV and UTV engine components lineup with reliable and convenient engine rebuild kits for Polaris 800 engines. Designed, developed, and tested specifically for Polaris RZR, Ranger, and Sportsman 800 models, these kits deliver improved performance and durability with less hassle and cost.

Stemming from the longstanding lineup of hardworking ATVs and UTVs found on ranches, farms, and job sites around the world, the recreational sport UTV segment has exploded over the last decade. One of the biggest players in this growth and recreational evolvement is the RZR 800 from Polaris. This platform set the stage for the high-performance, long-travel off-road cars we see today, but it also shares the same powerplant as many of its hard-working utility cousins, including the Ranger and Sportsman.

polaris rzr 800

Whatever the model it was driving, this 760cc, twin-cylinder 4-stroke proved to be a reliable platform with enough grunt to get the job done or put a smile on your face. However, after many seasons of use abuse, there are plenty of these engines out there begging for a refresh.

polaris rzr 800 engine

Thankfully, this is exactly where ProX shines. Affordable performance replacement parts delivering OEM or better reliability without the crazy costs and ordering hassle associated with sourcing OEM parts are core values ProX carries through all their products, and they're proud to apply it to what's now one of their most robust offerings with ProX Engine Rebuild Kits.

ProX polaris 800 engine rebuild kit

Polaris RZR / Ranger / Sportsman 800 Engine Rebuild Kits

  • Complete rotating and reciprocating rebuild kit, including:
    • Precision-machined, complete crankshaft assembly with proprietary design enhancements
    • OEM-quality, complete engine gasket kit and seals
    • Japanese-sourced main bearings
    • OEM-quality, AC8A cast pistons with added durability measures including skirt coating and hard anodizing
      • Piston kits include OEM-quality rings, wrist pin, and locks
    • A packet of Maxima assembly lube to aid in a smooth rebuild
  • Covers Polaris RZR, Ranger and Sportsman 800 models (complete model listed further down the page)

Ask your preferred dealer or call ProX USA to order!
800-321-1364 or 440-951-6600

The ProX R&D team sourced a complete 800 engine out of a RZR 800 and did extensive testing on their in-house dyno. The team first did some dyno pulls with the engine in stock configuration to gather benchmark data, not just recording horsepower and torque, but also noting any excessive knock and detonation. They then dissembled the engine and examined its components to understand the wear characteristics of the OEM components, allowing the engineering team to design improvements for these “weak” points into ProX components.

prox dyno

rzr 800 engine on dyno

The crankshaft assembly is the biggest engineering accomplishment of these kits. Going into it, the goal was to design and manufacture an assembly that could consistently deliver improved performance and longevity over the OEM counterpart. Using benchmark testing data and known points for improvement, the ProX Polaris 800 crankshaft uses a proprietary connecting rod design delivering optimal strength-to-weight characteristics. They are forged and heat treated for higher tensile strength and are shot peened to reduce stress risers – all together reducing the impact of engine operating stress and improving durability.

ProX polaris 800 crankshaft

ProX polaris 800 connecting rod

In the big end of the connecting rods, these crankshaft assemblies utilize graded big end bearings. What are graded bearings, and what advantage do they provide? Polaris 800 crankshafts use a slide-style bearing instead of a needle and cage style you might find in a dirt bike application. These slide bearings are similar to what’s used in the automotive sector, and the graded sizing allow for each crank to be built with a very specific bearing size in order to achieve highly precise bearing clearances. A fine-tuned bearing clearance ultimately translates to improved performance and longevity.

ProX polaris 800 crankshaft 2

Moving onto the crankshaft gear, the material hardness of the OEM crank proved to be sub-standard to what’s commonly seen for this type of use. The gear on the ProX crankshaft is constructed of a material that proved to retain greater hardness, even throughout extended run time in testing.

ProX polaris 800 crankshaft gear

Through experience gained both with decades of product development and first-hand use in the field, Wiseco knows a bottom-end rebuild is only as good as the main bearings that go into it. ProX sourced Japanese-made Koyo main bearings for use with these Polaris 800 crankshaft assemblies, helping insure longevity, smooth operation, and accurate specifications.

To aid in proper reassembly, these bottom-end rebuild kits for Polaris 800 engines include a complete engine gasket kit, including all the OEM-quality gaskets and seals needed for both a bottom and top-end rebuild.

ProX rzr 800 engine rebuild

In addition to the crankshaft assembly, main bearings and seals, and gasket kit, Polaris 800 Engine Rebuild Kits also include an OEM-quality, AC8A cast piston kit for each cylinder, a complete top end gasket kit including valve seals, and assembly lube.

ProX rzr 800 piston kits

The ProX pistons included were designed to improve durability and longevity beyond that of the OEM part thanks to an MOS2 skirt coating and hard anodizing treatment on the piston crown and in the top ring groove. The skirt coating helps reduce operating friction to improve performance and reduce skirt and cylinder wear while the hard anodizing protects the alloy from damaging combustion chamber conditions as well as preventing ring microwelding for a more reliable ring seal. These pistons were included in ProX’s dyno testing, done simultaneously with crankshaft testing in order to validate the complete rotating and reciprocating rebuild kit.

ProX polaris 800 pistons

ProX polaris 800 pistons hard anodize

Staying true to ProX's piston offering standards, these kits are available with pistons in A/B/C graded sizing. What this means is across each of the four different series of Polaris rebuild kit part numbers, each one is offered with 'A' sized pistons (standard bore), or 'B' or 'C' sized pistons, which increase bore size in 0.01mm increments, allowing customers and builders to maintain proper piston-to-wall clearance, even in cylinders that have worn slightly outside of their starting range.

The compression ratio delivered with the ProX pistons in these rebuild kits differs slightly depending on the specific application, but generally range from 10.0:1 to 10.2:1. The versatile gasket kits supplied, graded sized pistons, and versatile piston design allow 12 different model and year ranges of Polaris models to be covered under just 4 different part number series.

ProX polaris 800 pistons and gaskets

ProX Engine Rebuild Kits are available for 2008 – 2014 Polaris RZR 800 applications as well Ranger and Sportsman 800 applications, covering both standard and 6x6. Check out the complete list of models covered below:

Item Make Model Year


Polaris Sportsman 800 EFI Non-H.O.
Sportsman X2 800 EFI
Sportsman 800 EFI 6x6
Ranger 800 (All)
RZR 800 EFI (All)

2005 – 10
2007 - 09
2009 – 10
2008 - 10

Polaris Sportsman 800 EFI Non-H.O.
Sportsman 800 6x6
Ranger 800 EFI / Crew
Ranger 800 EFI 6x6
2011 – 14
2011 – 14
2011 – 14
2011 – 16
Polaris Sportsman 800 EFI H.O. 2008 - 09

RZR S 800
RZR 4 800

2011 - 14

Ask your preferred dealer or call ProX USA to order!
800-321-1364 or 440-951-6600

Whether it’s a Polaris RZR serving up family fun or a Ranger or Sportsman relied on to get work done, ProX Engine Rebuild Kits for Polaris 800 engines can help restore and improve performance and reliability for less hassle and cost over OEM components.

polaris rzr 800 mountains

polaris sportsman 800 work


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