VHM Cylinder Head Insert for TM RACING MX 85 1999-2012

The VHM cylinder head insert is designed for TM RACING MX 85 from 1999 to 2012. 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: AE32089-C, AE32089-E, AE32089-F
• Available versions: Version C (7.40 cc): ref. AE32089-C; Version E (7.60 cc): ref. AE32089-E; Version F (7.80 cc): ref. AE32089-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 : VHM SK33000.VITON · VHM SK33000
• Spark plug : NGK
• Coolant : TWIN AIR 1 L · MOTUL 1 L

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 C (7.40 cc): 7.40 cc, piston height -0.60 mm, squish 1.00 mm; Version E (7.60 cc): 7.60 cc, piston height -0.60 mm, squish 1.00 mm; Version F (7.80 cc): 7.80 cc, piston height -0.60 mm, squish 1.00 mm.

Compatibility

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

Fits:
TM RACING MX 85 2012
TM RACING MX 85 2011
TM RACING MX 85 2010
TM RACING MX 85 2009
TM RACING MX 85 2008
TM RACING MX 85 2007
TM RACING MX 85 2006
TM RACING MX 85 2005
TM RACING MX 85 2004
TM RACING MX 85 2003
TM RACING MX 85 2002
TM RACING MX 85 2001
TM RACING MX 85 2000
TM RACING MX 85 1999