VHM Cylinder Head Insert for YAMAHA YZ 85 2019-2026

The VHM cylinder head insert is designed for YAMAHA YZ 85 from 2019 to 2026. On a VHM cylinder head, the combustion chamber is an interchangeable insert (or dome). Changing the insert changes the chamber volume, and therefore the compression ratio, without modifying the head: you adapt the engine to the fuel, the terrain and your riding.

Key features

• Each version shows its three key figures: chamber volume, piston height and squish.
• Change the compression without machining the head, to suit the fuel and the terrain.
• Part number engraved on the insert.
• Fits VHM cylinder heads only.

Specifications

• Brand: VHM
• Manufacturer part numbers: AE32286-072, AE32286-032, AE32286-C, AE32286-029, AE32286-E, AE32286-040, AE32286-F
• Available versions: Version 072 (8 cc): ref. AE32286-072; Version 032 (8.20 cc): ref. AE32286-032; Version C (8.20 cc): ref. AE32286-C; Version 029 (8.40 cc): ref. AE32286-029; Version E (8.40 cc): ref. AE32286-E; Version 040 (8.60 cc): ref. AE32286-040; Version F (8.60 cc): ref. AE32286-F
• Engine: 2-stroke

Choosing the right version

Each version is defined by three dimensions: the chamber volume in cm³ (spark plug hole included), the piston height at top dead centre relative to the top of the cylinder (“−0.55”: piston 0.55 mm below the cylinder face) and the squish, the minimum gap between piston and insert. A smaller volume raises compression: more bottom end and mid-range, but a higher-octane fuel may become necessary.

When to change the insert?

• Switch to a different fuel (98 or race fuel with a higher octane rating).
• Engine knocking (pinking) or running hot: compression too high for the fuel.
• You want more torque on tight or sandy terrain.

Change the insert when you change fuel or type of riding, or if the engine pinks. The insert's three dimensions (volume, piston height, squish) must match your engine.

Fitting tips

1. The insert is changed with the cylinder head removed.
2. Check that the actual height of your piston at top dead centre matches the figure given for the insert.
3. Replace the VHM head O-rings every time you take it apart.
4. Check the squish with solder wire before riding.
5. Tighten the head to the recommended torque, in a criss-cross pattern and in several stages, then fit a new spark plug.

Why VHM?

Since 1995, VHM has been designing racing engine parts for two-strokes: cylinder heads with interchangeable inserts, combustion chamber inserts, crankshafts and connecting rods. A specialist brand, used to fine-tune an engine's power without transforming it.

Spare parts and items to plan

• VHM head O-rings : ATHENA M752005600094 · ATHENA M752008300094
• Spark plug : NGK 6801 · NGK 3830
• Coolant : LIQUI MOLY 1 L · TWIN AIR

Frequently asked questions

Will it fit my original cylinder head?
No: VHM inserts only fit VHM cylinder heads.

Which version should I choose?
Choose according to your engine and fuel. Version 072 (8 cc): 8.00 cc, piston height +0.00 mm, squish 1.30 mm; Version 032 (8.20 cc): 8.20 cc, piston height +0.00 mm, squish 1.30 mm; Version C (8.20 cc): 8.20 cc, piston height +1.60 mm, squish 1.30 mm; Version 029 (8.40 cc): 8.40 cc, piston height +0.00 mm, squish 1.30 mm; Version E (8.40 cc): 8.40 cc, piston height +1.60 mm, squish 1.30 mm; Version 040 (8.60 cc): 8.60 cc, piston height +0.00 mm, squish 1.30 mm; Version F (8.60 cc): 8.60 cc, piston height +1.60 mm, squish 1.30 mm.

Compatibility

Check the exact model and year of your bike in the list below before ordering.

Fits:
YAMAHA YZ 85 2026
YAMAHA YZ 85 2025
YAMAHA YZ 85 2024
YAMAHA YZ 85 2023
YAMAHA YZ 85 2022
YAMAHA YZ 85 2021
YAMAHA YZ 85 2020
YAMAHA YZ 85 2019