VHM Cylinder Head Insert for KTM SX 50, HUSQVARNA TC 50 and GAS GAS MC 50 2009-2023

The VHM cylinder head insert is designed for KTM SX 50, HUSQVARNA TC 50 and GAS GAS MC 50 from 2009 to 2023. The insert forms the combustion chamber of the VHM head. Its volume sets the engine's compression: a small volume gives more bottom end and mid-range, a larger volume keeps the engine smoother and longer-revving.

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: AE32170-C, AE32170-E
• Available versions: Version C (4 cc): ref. AE32170-C; Version E (4.20 cc): ref. AE32170-E
• 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?

Founded in 1995, VHM specialises in racing engine parts for motocross, road racing and karting. The brand started out with cylinder heads featuring interchangeable combustion chambers, which became its speciality, and then developed crankshafts, connecting rods and gasket kits.

Spare parts and items to plan

• VHM head O-rings : ATHENA M752005200094 · ATHENA M752007800094
• Spark plug : NGK · NGK LR8B
• 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 C (4 cc): 4.00 cc, piston height +2.45 mm, squish 0.60 mm; Version E (4.20 cc): 4.20 cc, piston height +2.45 mm, squish 0.60 mm.

Compatibility

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

Fits:
GAS GAS MC 50 2023
GAS GAS MC 50 2022
GAS GAS MC 50 2021
HUSQVARNA TC 50 2023
HUSQVARNA TC 50 2022
HUSQVARNA TC 50 2021
HUSQVARNA TC 50 2020
HUSQVARNA TC 50 2019
HUSQVARNA TC 50 2018
HUSQVARNA TC 50 2017
KTM SX 50 2023
KTM SX 50 2022
KTM SX 50 2021
KTM SX 50 2020
KTM SX 50 2019
KTM SX 50 2018
KTM SX 50 2017
KTM SX 50 2016
KTM SX 50 2015
KTM SX 50 2014
KTM SX 50 2013
KTM SX 50 2012
KTM SX 50 2011
KTM SX 50 2010
KTM SX 50 2009