Reinforced head gasket Coventry Climax FWA FWB FWE

The Coventry Climax engines covered

The Coventry Climax FWA (1,098 cc, 72.4 mm bore), FWB (1,460 cc, 76.2 mm bore) and FWE (1,216 cc, FWB bore and FWA stroke) are four-cylinder engines of the FW family, with overhead camshaft, fitted to the Lotus Eleven, Lotus 17, Lotus Elite, the TVR Grantura and other light cars of the 1950s and 1960s.

The manufacturer publishes nothing on the original gasket of these engines: neither its part number, nor its bore, nor its construction, nor its thickness. It was sized for the combustion pressure of the day; if that rises, the clamping load fades, the head lifts and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

The gasket does not seal alone: the fasteners that clamp the head onto the block count just as much. CFM-20 pairs a galvanized steel core with a soft asbestos-free compound that makes up for small irregularities in the gasket faces. On an FW, retighten the head to the procedure in your engine's workshop manual.

This page presents four part numbers from the American maker Cometic, a specialist in racing gaskets, all in the CFM-20 construction: 74 mm at 1.50 mm for the FWA, 78 mm at 1.09 mm and at 1.50 mm for the FWB and FWE, 80 mm at 1.09 mm for all three engines. Each is sold individually: one gasket per engine.

Technical specifications

A gasket's volume is the space it keeps free above each cylinder. It adds to the combustion chamber and reduces the compression ratio; only gaskets of the same bore can be compared. Between the three bores offered here, 74, 78 and 80 mm, it varies with the diameter.

Preparation and fitting

Before fitting, check the flatness of the head and block with a straight edge, and have either one resurfaced if needed. Cometic checks the flatness of each of its CFM-20 gaskets. On an FWA, FWB or FWE, this check is made with the head removed and cold.

Technical guide

The construction offered

Choosing bore and thickness

Gasket bore. The Cometic CFM-20 gasket is offered in three bores: 74 mm (C4301-059), 78 mm (C4139-043 and C4139-059) and 80 mm (C4229-043).

Thickness. For the original gaskets of these engines, no thickness is published. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

With no published original thickness, use a dial gauge to measure how far the pistons stand above the block's gasket face: this gives the clearance left between piston and head and guides the choice between 1.09 mm and 1.50 mm.

The brand

Cometic Gasket, Inc. is an American maker of gaskets and sealing solutions for engines, founded in 1989 in Concord, Ohio. It made its name with the made-to-measure gasket, cut to the bore and thickness requested, and makes everything in the United States from American raw materials. Small FW engines are the kind this made-to-order approach suits well.

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 gaskets offered, 74, 78 or 80 mm 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 numbers on this page suit the Coventry Climax FWA, FWB and FWE engines: the 74 mm to the FWA alone, the 78 mm to the FWB and FWE, the 80 mm to all three. Check your engine and measure your cylinder bore before ordering.

Why switch to a reinforced gasket?

When the original gasket reaches its limit, this CFM-20 gasket takes over: the steel core holds its shape under combustion pressure, and the soft compound on both faces follows the small flaws of the head and block. The FWA, FWB and FWE find here the gasket for their bore.

On a hard-driven competition engine, the head gasket is the first part to give way, the weak point of the top end. A reinforced gasket rules out the leak, whereas the head removal that follows costs far more than the gasket. This holds for the FWA, FWB and FWE as for any hard-driven engine.