Reinforced head gasket Mitsubishi 4G63 4G63-T

The Mitsubishi engines covered

The Mitsubishi petrol engines 4G63 and 4G63-T, of 2.0 litres, power in particular the Galant, Eclipse, Lancer (including the Evo versions), Outlander, Carisma, Space Runner, Santamo and Dion detailed below.

For these engines, our sources confirm no original gasket part number: the original bore, construction and thickness therefore stay unstated. The standard gasket is sized for standard pressure: when that climbs, clamping gives way, the cylinder head lifts and coolant reaches a cylinder.

Reinforced cylinder head gaskets

Sealing does not rest on the gasket alone: the bolts or studs that clamp the head to the block count just as much. Above 100 N/mm², a composite gasket settles for good; the 301 stainless steel of MLS and MLX gaskets withstands 517 N/mm², 5 times more, and regains its shape after every combustion.

This page gathers the part numbers of Athena and Cometic, makers of competition gaskets, in three constructions: the Athena MLS with Gas Stopper, the multi-layer steel Cometic MLS and the Cometic MLX with chamber stopper. The bores run from 85 to 87 mm and the thicknesses from 0.69 to 3.56 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 void it leaves above each cylinder. It adds to the combustion chamber and lowers the compression ratio, the more so the larger it is. Compare these figures only between gaskets of the same bore.

Preparation and fitting

Before fitting, check the flatness of the cylinder head and block faces with a straightedge, and have any warped face machined. Add no sealant of any kind: Cometic gaskets are supplied coated.

Technical guide

The three constructions offered

	Athena MLS Between two and five AISI 301 stainless steel layers, laser cut, stamped, then riveted. A layer folded back on itself, the Gas Stopper, surrounds each cylinder and carries the clamping load to the combustion chamber, while embossments seal the water and oil passages. The outer layers receive a two-coat finish: the first withstands high temperatures and fills small flaws in the block and head, the second, silicone-based, stops the gasket sticking at removal. It is Athena's all-steel answer, from the tuned naturally aspirated engine to moderate boost.
	MLS Cometic A stack of stamped stainless steel sheets, riveted together. Around each cylinder and each fluid passage, the outer sheets carry active embossments that do the sealing. Moderate clamping is enough, and the bore barely distorts. It is the versatile construction, from the tuned naturally aspirated engine to moderate boost.
	Cometic MLX A multi-layer stainless steel gasket whose folded centre sheet forms a stopper around each combustion chamber. That stopper concentrates the clamping load on the bore and limits crushing of the gasket. It suits boosted engines and high combustion pressures.

Choosing bore and thickness

Gasket bore. Athena MLS is available in 86.5 mm (338494R); Cometic MLS is offered in 85 mm (C4157), in 85.5 mm (C4233), in 86 mm (C4156, C4234) and in 87 mm (C4591, C4235); Cometic MLX in 87 mm (C4956, C4957).

Thickness. No original thickness is confirmed for these two engines. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

Should you pick a thickness thinner than the original, begin by measuring with a dial gauge how far the pistons protrude above the block deck: this figure gives the clearance left between piston and cylinder head.

The two brands

	Athena S.p.A. is an Italian maker of gaskets and engine components, with its head office and main plant in Alonte, in the Veneto. The group also produces in Spain, the United States, Brazil and India. Its multi-layer gaskets are fitted as original equipment by car makers, and its competition range is designed and built entirely in Italy.
	Cometic Gasket, Inc., founded in 1989 in Concord, Ohio, is an American maker of engine gaskets and sealing solutions. Its reputation rests on the made-to-measure gasket, cut to the bore and thickness requested. All production stays in the United States, from 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 bore of the original gasket, a figure not confirmed 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: no original part number confirmed.

Important: the part numbers on this page are intended for the Mitsubishi 4G63 and 4G63-T engines of the vehicles in the table above: note your vehicle's engine code, then choose the bore, before ordering.

Why switch to a reinforced gasket?

Once the original gasket reaches its limit, the reinforced one takes over: under higher combustion pressure it holds its shape and is not crushed flat.

On a turbocharged, supercharged or raised-compression engine, the head works harder and the gasket becomes the most exposed part of the top end. A reinforced gasket prevents the gas or coolant leak, and the head removal that follows, with the vehicle off the road.