Reinforced head gasket Triumph Spitfire 1500 FM11

The Triumph engines covered

The FM11 petrol engine (1.5 litre, four cylinders) powers the Triumph Spitfire 1500 listed below.

The part number of the original gasket is not published by the manufacturer, nor are its bore, construction or thickness. It is meant for standard combustion pressure: when that pressure climbs, the head loses its clamping force, lifts off the block and lets coolant into a cylinder.

Reinforced cylinder head gaskets

The seal does not rest on the gasket alone: it also depends on the fasteners that press the head onto the block. Copper at 99.9% resists corrosion, deforms without breaking and conducts heat well, without turning brittle when hot.

This page offers the part numbers of the American maker Cometic, a specialist in racing gaskets, in one construction only: copper. Their bore is 74 mm and their thickness 0.81 or 1.09 mm. As a reminder, the gasket bore should be at least 0.5 mm larger than the real cylinder bore. They are sold individually, one gasket being enough for an engine.

Technical specifications

The volume of a gasket is the space it keeps free above each cylinder. It adds to the combustion chamber and reduces the compression ratio, the more so as it is large. Values can only be compared 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, then have them resurfaced if needed. Cometic checks the flatness of its copper gaskets itself.

Technical guide

The construction offered

Choosing bore and thickness

Gasket bore. The Cometic copper gasket is made in 74 mm (C4153), that bore only.

Thickness. The manufacturer does not publish 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.

As the original thickness remains unknown, use a dial gauge to read how far your pistons stand above the block, above all if the removed gasket is thicker than 0.81 mm: that figure decides the clearance left between piston and head.

The brand

Cometic Gasket, Inc., an American company making gaskets and sealing solutions for engines, was founded in 1989 in Concord, Ohio. It made its name with the custom gasket, cut to the bore and thickness requested. Everything is made 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, not published 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: not published by the manufacturer.

Important: the part number on this page is reserved for the FM11 engine: check your car's engine code before ordering.

Why switch to a reinforced gasket?

This copper gasket takes over when the original gasket reaches its limits: pure copper is ductile and stays supple when hot, which keeps the seal between head and block.

A turbo, a supercharger or a raised compression ratio expose the head gasket first, the weakest link of the top end. Opting for a reinforced gasket protects the engine: it avoids the leak and the head removal that follows.