VHM cylinder head Yamaha YZ 250 88-98 + insert C 20.00 cc

HEAD AND INSERT INCLUDED: VHM head AA33187 + insert AE32300-C (combustion chamber 20.00 cc). Once fitted the head is ready to ride, nothing else to buy. Golden VHM two-stroke cylinder head with an exchangeable combustion chamber. It is designed to keep the engine's power throughout the whole race, not just the first laps: the improved water duct takes heat away from the combustion chamber more effectively. Made from a high-quality alloy and sealed with O-rings instead of a conventional gasket. WHAT THE INSERT IS AND WHY YOU NEED IT The VHM head has two parts: the golden cooled body and the chamber fitted into it — the insert. The insert sets the combustion chamber volume, i.e. the compression. Smaller volume = higher compression = more pull, but it needs higher-octane fuel. Larger volume = lower compression = the engine revs out more freely and tolerates pump fuel. When you change fuel, track or elevation you swap only the insert, not the whole head. WHICH INSERT TO CHOOSE (OEM piston) • AE32300-B — 19.50 cc • AE32300-C — 20.00 cc • AE32300-E — 20.50 cc (VHM standard) • AE32300-F — 21.00 cc If in doubt, take the VHM standard: AE32300-E (20.50 cc). BENEFITS • more engine power • better heat transfer • more resistance to detonation • exchangeable combustion chambers Spare O-rings: seal kit SK33000. Fits: Yamaha YZ 250 (1988–1998).