Reinforced head gasket Opel Vauxhall 2.0 Turbo LNF A20NHT A20NFT

The Opel engines covered

The LNF, A20NHT and A20NFT turbocharged petrol engines, 2.0 litre units, power the Opel and Vauxhall Insignia, the Astra J GTC OPC and VXR, as well as the Saab, Chevrolet, Pontiac, Saturn and other models listed in the compatibility table below.

The original gasket carries the part number 12 589 346. Its bore is 87.05 mm; the manufacturer publishes neither its construction nor its thickness. It is designed for the standard combustion pressure: when that rises, the clamping tension drops, the cylinder head lifts a little and coolant enters a cylinder.

Reinforced cylinder head gaskets

The gasket alone does not make the seal: the fasteners clamping the head onto the block contribute half of it. Beyond 100 N/mm² of stress, a composite gasket is crushed for good; the 301 stainless steel of MLX gaskets withstands 517 N/mm², 5 times more, and regains its shape at every combustion.

This page presents the part numbers of Cometic, an American maker of competition gaskets, in a single construction: the MLX with chamber stopper. The gasket bore is 88 mm, 0.95 mm more than the original gasket's, and seven thicknesses are offered, from 0.91 mm to 1.32 mm, enough to adjust the compression ratio without touching the pistons or the cylinder head. As a rule, the gasket bore chosen is at least 0.5 mm larger than the actual cylinder bore. Each part number is sold individually, one gasket per engine.

Technical specifications

A gasket's volume is the free space it leaves above each cylinder. It adds to the combustion chamber and lowers the compression ratio, all the more as the gasket is thick. Compare these values only between gaskets of the same bore.

Preparation and fitting

Before fitting, run a straight edge over the head and the block to check their flatness, and have them resurfaced if needed. These gaskets are fitted dry: Cometic supplies them already coated, with no sealing paste to add.

Technical guide

The construction offered

Cometic MLX An all stainless steel multilayer gasket whose intermediate sheet, folded back on itself, draws a stopper around each chamber and carries a high-temperature coating. Clamping pressure is concentrated where it is useful, without distorting the bore any further. It is the toughest all-steel gasket, reserved for heavy boost; it is offered here in 88 mm only.

Choosing bore and thickness

Gasket bore. The Cometic MLX is offered here in 88 mm only (C15256).

Thickness. Opel publishes no thickness for the original gasket. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

With no published original thickness, use a dial gauge to measure how far the pistons stand proud of the block deck, especially after resurfacing: this protrusion sets the clearance left between piston and head, and so the thickness to pick among the seven offered.

The brand

Cometic Gasket, Inc., an American company founded in 1989 in Concord, Ohio, designs gaskets and sealing solutions for engines. Its speciality is the made-to-measure gasket, produced at the bore and thickness wanted. All manufacturing is American, with American raw materials.

Advantages over the original gasket

When a reinforced gasket becomes necessary

• Adding forced induction, or raising boost on an already turbocharged engine
• Cylinder rebored beyond what the 87.05 mm bore of the original gasket covers
• Looking for a compression ratio different from standard, higher or lower
• Engine that has already lost its gasket, or is consuming coolant
• Competition use, where the gasket goes through repeated temperature rises

Vehicle compatibility

OEM part number: 12 589 346.

Important: the part numbers on this page suit only the LNF, A20NHT and A20NFT engines: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket reaches its limit, the reinforced gasket carries on: under a higher combustion pressure, it keeps its shape instead of being crushed.

A turbo blowing harder, a supercharger or a raised compression ratio: as soon as power rises, the head gasket is the first link to give way in the top end. Choosing a reinforced gasket means choosing reliability: you spare yourself the failure and the head removal that follows.