BRC 510cc CONVERSION KIT YAMAHA YZ 250 1999-2025

This BRC 510cc conversion kit is a bolt-in two-stroke engine conversion for Yamaha YZ250-based applications from 1999 to 2025, intended to build a larger-capacity counterbalanced engine by reusing selected parts from a donor YZ250 engine. In practical terms, it allows the original YZ250 platform to be rebuilt into a motocross-focused engine package with stronger output and smoother delivery, rather than relying on a complete replacement engine assembly.

Features

• Bolt-in conversion based on the Yamaha YZ250 platform


• Developed as a 500cc-class counterbalanced two-stroke conversion


• Motocross-focused power delivery


• Pneumatic power valve system for smooth, linear response


• Triple-blade power valve arrangement for stronger bottom-end response


• Kick-start compatible


• Fitted decompression button to assist starting


• Integral counterbalance shaft to reduce vibration


• Supplied with a purpose-built exhaust pipe and silencer


• Intended to run with the stock carburettor

Donor Components Required

• Requires components from a donor Yamaha YZ250 engine from the listed applications


• Reuses original engine parts to build the 510cc engine


• Accepts donor Yamaha YZ250 and YZ250X transmission components


• Donor engine parts used in the build include the clutch assembly, kicker assembly, water pump, intake, ignition and covers where possible

Specifications

• Output: 60+ hp


• Torque: 50+ ft-lb


• Bore: 89 mm


• Stroke: 80 mm


• Compression ratio: 12.8:1


• Transmission oil capacity: 1100 cc


• Fuel requirement: minimum 91-octane petrol


• Premix ratio: 50:1


• Premix ratio for snowbike and desert use: 32:1

Cross-Reference OEM Part Numbers

• Neutral switch block-off kit: 08-05-012


• Service piston: Vertex 22447


• Connecting rod: ProX 03.1406


• Connecting rod: Wossner P2044


• Left-side transmission output shaft cylindrical roller bearing: NJ205EC3


• Equivalent replacement bearing: KTM 49030023000

Installation Notes

• Both lower radiator fitting locations must be relocated using the supplied 6061-T6 caps and fittings


• The donor YZ250 cylinder-head hose must be shortened to suit the taller cylinder


• 2010 and older donor YZ250 engines require a neutral switch block-off kit


• Uses readily available consumables including KTM-sourced bearings and seals, and gaskets made by Cometic

Vehicle Fitments

• Yamaha YZ250, 2005-2025, aluminium frame models, fits without fabrication


• Yamaha YZ250, 1999-2004, steel frame models, minor modification required