Reinforced cylinder head gasket TVR AJA6 AJB6 APA6 APJ6 P640

The TVR engines covered

The TVR six-cylinder petrol engines AJA6, AJB6, APA6, APJ6 and P640, of 3.6 and 4.0 litres, are fitted to the Cerbera, Tuscan, Tamora, T350 C, Sagaris and Typhon models detailed below.

TVR publishes neither the part number of the original gasket of these engines, nor its bore, nor its thickness, nor its construction. That gasket is sized for standard pressure: when it rises, clamping relaxes, the cylinder head lifts and coolant enters a cylinder.

Reinforced cylinder head gaskets

The head gasket does not seal on its own: the fasteners that clamp the head to the block play as large a part as it does. Beyond 100 N/mm², a composite gasket settles permanently; the 301 stainless steel of MLS gaskets withstands 517 N/mm², 5 times more, and returns to shape at every combustion.

This page presents the part numbers of Cometic, an American maker of competition gaskets, in a single construction: the multi-layer steel MLS. The gaskets exist in a 96.5 mm bore, with one part number in 98.5 mm, 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

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 is large. Compare these values only between gaskets of the same bore.

Preparation and fitting

Before fitting, lay a straight edge across the head and block faces to check their flatness, then have them machined if necessary. Do not apply sealing paste: Cometic gaskets arrive already coated.

Technical guide

The construction offered

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

Choosing bore and thickness

Gasket bore. The Cometic MLS is offered in 96.5 and 98.5 mm (C4527), depending on the part number.

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

If you choose a thickness below the original, first measure with a dial gauge how far the pistons protrude above the block deck: that figure gives the clearance remaining between piston and head.

The brand

Cometic Gasket, Inc., an American company created in 1989 in Concord, Ohio, makes engine gaskets and sealing solutions. Its know-how lies in the made-to-measure gasket, cut to the bore and thickness required. All 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 TVR 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 TVR engines AJA6, AJB6, APA6, APJ6 and P640: note your vehicle's engine code, then check the bore, before ordering.

Why switch to a reinforced gasket?

When the original gasket is at its end, the reinforced gasket takes over: at higher combustion pressure it keeps its shape and does not crush.

With a turbo, a supercharger or a raised compression ratio, the loads on the cylinder head grow and the gasket becomes the most stressed part of the top end. A reinforced gasket avoids the gas or coolant leak, and the head removal that follows, with the vehicle off the road.