Reinforced cylinder head gasket Mitsubishi 420A 2.0L

The Mitsubishi engines covered

The 2.0-litre Mitsubishi 420A petrol engine is fitted to the Eclipse II in the version detailed below.

Mitsubishi publishes neither the part number of this engine's original gasket, nor its bore, nor its thickness, nor its construction. That gasket is designed for standard pressure: when it climbs, clamping weakens, the cylinder head lifts and coolant reaches a cylinder.

Reinforced cylinder head gaskets

The head gasket does not seal alone: the fasteners that clamp the head to the block count as much as it does. Above 100 N/mm², a composite gasket settles with no recovery; the 301 stainless steel of MLS gaskets holds up to 517 N/mm², 5 times more, and regains its shape at every combustion.

This page gathers the part numbers of Cometic, an American maker of competition gaskets, in a single construction: the multi-layer steel MLS. The gaskets are offered in 87.5 mm and 88.5 mm bores, and in 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

The gasket volume is the void it leaves above each cylinder. It adds to the combustion chamber and lowers the compression ratio, the more so as it grows. Compare these values only between gaskets of the same bore.

Preparation and fitting

Before assembly, check with a straight edge that the head and block faces are flat, and have them resurfaced if needed. Use no sealing paste: Cometic gaskets are supplied already coated.

Technical guide

The construction offered

MLS Cometic Stainless steel layers, stamped and then fastened together with rivets. The outer layers show active beads around each cylinder and each fluid passage. Moderate tightening is enough to seal and the bore distorts very little. This versatile construction suits everything from the prepared naturally aspirated engine to moderate boost.

Choosing bore and thickness

Gasket bore. Cometic MLS is offered in 87.5 mm (C5497) and in 88.5 mm (C5498).

Thickness. Mitsubishi gives no thickness for the original gasket of this engine. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

Before settling on a thickness below the original, read with a dial gauge how far the pistons stand proud of the block face: that figure shows the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American company founded in 1989 in Concord, Ohio, that designs engine gaskets and sealing solutions. It made its name with the made-to-measure gasket, cut to the bore and thickness requested. All of its production stays in the United States, with American 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, which Mitsubishi does not publish 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: part number not published by the manufacturer.

Important: the part numbers on this page match the Mitsubishi 420A engine: note your vehicle's engine code, then check the bore, before placing an order.

Why switch to a reinforced gasket?

When the original gasket is no longer enough, the reinforced gasket steps in: under higher combustion pressure it keeps its shape and does not crush.

With a turbo, a supercharger or a raised compression ratio, the head takes higher loads and the gasket becomes the most stressed part of the top end. A reinforced gasket prevents the gas or coolant leak, and the head removal that follows.