Reinforced head gasket Jaguar Land Rover 5.0 V8 AJ133

The Jaguar and Land Rover engines covered

The AJ133 engine is a V8 of 5.0 litres with 32 valves, offered in a naturally aspirated version (508PN) and a supercharged version (508PS). It powers the Jaguar and Land Rover models in the compatibility table below and takes two head gaskets, one per cylinder bank.

The original gasket carries part number AJ811409. The manufacturer publishes neither its bore, nor its thickness, nor its construction. It is sized for standard combustion pressure: when that rises, the clamping load falls, the head lifts and coolant finds its way into a cylinder.

Reinforced cylinder head gaskets

The gasket does not guarantee the seal on its own: it also depends on the fasteners that clamp the head onto the block. A composite gasket is permanently crushed above 100 N/mm², whereas the 301 stainless steel of the MLX withstands 517 N/mm², 5 times more, and recovers its shape at every combustion.

This page brings together the part numbers of Cometic, an American maker of racing gaskets, in a single construction: the MLX with its chamber stopper. The gasket bore is 93 mm and the thickness offered is 1.016 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. As the engine takes two gaskets, one per cylinder bank, order both part numbers: C15000 for the left side and C15001 for the right side.

Technical specifications

Gasket volume is the space the gasket leaves free above each cylinder. It adds to the combustion chamber volume: the larger it is, the lower the compression ratio. Only compare these figures between gaskets of the same bore.

Preparation and fitting

Check the flatness of the head and block with a straightedge before fitting, and have them resurfaced if needed. No sealant is needed: Cometic supplies these gaskets already coated.

Technical guide

The construction offered

Cometic MLX Embossed stainless steel sheets whose folded centre sheet forms a stopper around the combustion chamber, under a high-temperature coating. The clamping load rises locally without distorting the bore any further. It is the toughest of the all-steel gaskets, for high boost pressures; here it comes only in 93 mm.

Choosing bore and thickness

Gasket bore. The Cometic MLX only exists here in 93 mm (C15000 and C15001).

Thickness. The manufacturer gives no thickness for the original gasket AJ811409. 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 is not published, use a dial gauge to measure how far the pistons stand above the block deck, especially after resurfacing: it sets the clearance that remains between piston and cylinder head.

The brand

Cometic Gasket, Inc., founded in 1989 in Concord (Ohio), is a US maker of gaskets and sealing solutions for engines. It specialises in made-to-order gaskets, in the bore and thickness requested, built entirely in the USA from 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 93 mm bore of the gaskets offered 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: AJ811409.

Important: the part numbers on this page are meant only for the AJ133, 508PN and 508PS engines, which take two gaskets, one per cylinder bank. Check your vehicle's engine code before ordering. Supplier part numbers: C15000-040 for the left side, C15001-040 for the right side.

Why switch to a reinforced gasket?

Where the original gasket reaches its limits, the reinforced one takes over: under higher combustion pressure, it keeps its shape instead of being crushed.

When power climbs, through a supercharger, a turbo or a raised compression ratio, the head gasket is the first link in the top end to give way. A reinforced gasket spares you the leak and the cylinder head removal that follows, far costlier than the part itself.