Reinforced cylinder head gasket Jaguar 3.8 L 7R and TU

The Jaguar engines covered

The Jaguar XK inline six of 3.8 litres, identified by the codes 7R and TU, powers the E-Type Series 1, Mark II, Mark IX, Mark X, S-Type and XK 150 models detailed below.

None of our sources confirms an original gasket part number for these engines, so the standard bore, construction and thickness are left unstated. The standard gasket is sized for the original combustion pressure: once that pressure climbs, clamping is lost, the head lifts and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

Sealing does not depend on the gasket alone: the fasteners that clamp the head onto the block matter just as much. Beyond 100 N/mm², a composite gasket takes a permanent set; the 301 stainless steel of MLS gaskets withstands 517 N/mm², five times more, and springs back with every combustion.

This page gathers the part numbers of Cometic, an American maker of competition gaskets, in two constructions: the multi-layer steel MLS and the CFM-20, with a steel core covered by an asbestos-free compound. The bores are 87, 88, 88.5 and 89 mm and the thicknesses run from 0.457 to 3.556 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

A gasket's volume is the free space it leaves over each cylinder. It is added to the combustion chamber and lowers the compression ratio all the more as it grows. Only gaskets of the same bore can be compared with one another.

Preparation and fitting

At assembly, first check the flatness of the head and the block with a straightedge, and have whichever of the two is warped machined true. No gasket sealant is needed: Cometic gaskets are supplied already coated.

Technical guide

The two constructions offered

	CFM-20 Cometic A galvanized steel core covered on both faces with a soft asbestos-free compound. This laminated construction, part metal and part fibre, combines the strength of steel with the softness of the compound. It is offered here in three bores, 87, 88 and 89 mm, and in two thicknesses, 1.09 and 1.50 mm.
	MLS Cometic A stack of stainless steel plates, embossed and riveted together. The outer plates carry active beads around every cylinder and every fluid passage. A moderate clamping load is enough to seal, and the bore distorts very little. This all-round construction suits anything from a tuned naturally aspirated engine to modest boost.

Choosing bore and thickness

Gasket bore. Cometic MLS is offered in 88 mm (C4282, C14063-050, H1763SP4050XP), in 88.5 mm (C14082-050) and in 89 mm (C4306); the CFM-20 in 87 mm (C4305), in 88 mm (C14041-059) and in 89 mm (C4125).

Thickness. No original thickness is confirmed for these engines. 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, use a dial gauge to read how far the pistons stand proud of the block face: that figure sets the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is a US company founded in 1989 in Concord, Ohio, that specialises in engine gaskets and sealing solutions. Its reputation rests on the made-to-measure gasket, cut to the bore and thickness requested and manufactured entirely 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 gaskets offered (87 to 89 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: no confirmed original part number.

Important: the gaskets on this page are listed for the 3.8 litre XK engine in the survey below, at Jaguar. For any other vehicle, find the engine code first before placing an order.

Why switch to a reinforced gasket?

When the standard gasket has reached the end of its tether, the reinforced gasket steps in: under higher combustion pressure it keeps its geometry instead of crushing.

Add a turbo or a supercharger, or raise the compression ratio, and the head works harder while the gasket becomes the first weak point of the top end. A reinforced gasket prevents the leak of gas or coolant and the head removal that follows, with the car off the road.