Yamaha YZ250 BRC 510cc Engine Conversion Kit 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

NOTE* UK SHIPPING COSTS MAY VARY DEPENDING ON ZONE. INTERNATIONAL SHIPPING IS WELCOME IF YOU ARRANGE IT YOURSELF (INSURED)