Reinforced cylinder head gasket Fiat 1.5 138A2.000 138A4.000

The Fiat engines covered

The 1.5 litre Fiat petrol engines 138 A2.000 and 138 A4.000 are fitted to the Ritmo (hatchback and convertible) and the X 1/9 listed below.

This original gasket carries the part number 4431654. Its bore is 87 mm; Fiat publishes neither its construction nor its thickness. It is designed for standard combustion pressure: when that pressure rises, the clamping load weakens, the cylinder head lifts and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

The gasket is not alone in sealing: the fasteners play an equal part, by clamping the cylinder head to the block. From 100 N/mm² of admissible stress, a composite gasket is crushed permanently; the 301 stainless steel of MLS gaskets withstands 517, 5 times more, and flexes back to shape with every combustion.

This page presents the part number from Cometic, an American maker of racing gaskets, for a single construction: the multi-layer steel MLS. The gasket has an 88 mm bore, against 87 mm for the original gasket, and a thickness of 1.12 mm. 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 space it leaves free above each cylinder. It enlarges the combustion chamber and so reduces the compression ratio; the comparison is only valid between gaskets of the same bore.

Preparation and fitting

Start by checking with a straight edge that the cylinder head and block are flat, then have them resurfaced if needed. Cometic supplies the gasket coated: add no sealing paste.

Technical guide

The construction offered

Cometic MLS Stainless steel plates, stamped, stacked and joined by rivets. The outer plates carry active beads around each cylinder and each fluid passage. A moderate tightening torque is enough to seal and the bore deforms little. It is the versatile gasket, from a prepared naturally aspirated engine to moderate forced induction.

Choosing bore and thickness

Gasket bore. The Cometic MLS is offered in 88 mm (C4952), in that bore only.

Thickness. Fiat does not disclose the thickness of the original gasket. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

Since the original thickness is not published, measure with a dial gauge how far the pistons stand above the block, especially if the removed gasket is thicker than 1.12 mm: that value gives the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American maker of engine gaskets and sealing products, founded in 1989 in Concord, Ohio. It made its name with the custom gasket, cut to the bore and thickness requested. All of its manufacturing 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 87 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: 4431654.

Important: the part number on this page fits only the engines 138 A2.000 and 138 A4.000: check your vehicle's engine code before placing an order.

Why switch to a reinforced gasket?

When the original gasket reaches its limit, the reinforced gasket carries on: at higher combustion pressure it keeps its thickness and shape without crushing.

A turbo, a supercharger or a higher compression ratio raises the load on the head gasket, the first weak link of the top end. Choosing a reinforced one avoids the leak, and the cylinder head removal that follows, with the labour and parts cost of doing the job twice.