Reinforced cylinder head gasket Toyota Lexus 1UZ-FE V8 4.0L

The Toyota engines covered

The V8 of 4.0 litres, the Toyota 1UZ-FE, powers the Lexus LS 400, GS 400 and SC 400 as well as the Toyota Celsior, Crown, Soarer and Aristo, in the version detailed below; the Cometic part numbers on this page are announced by the maker for the 1UZ-FE.

Toyota gives the part number 11115-50020 for the original gasket of this engine, but publishes neither its bore, nor its thickness, nor its construction. Each bank of four cylinders has its own head and gasket, sized for the standard pressure: as it climbs, the clamping load fades, the head lifts off the block and coolant passes into a cylinder.

Reinforced cylinder head gaskets

The head gasket does not seal on its own: the fasteners that press the Toyota head onto the block count as much as it does. Above 100 N/mm², a composite gasket settles for good; the 301 stainless steel of MLS gaskets withstands up to 517 N/mm², 5 times more, and recovers its shape at every combustion.

This page gathers the part numbers of Cometic, an American maker of competition gaskets, under a single construction: MLS, a multi-layer steel design. The V8 needs two different gaskets, one per bank, and each bank comes in several bores. They come in bores of 87.5, 89 and 92.5 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 and for one cylinder bank only: one is needed on the right and one on the left.

Technical specifications

The gasket volume is the empty space it leaves above each Toyota cylinder. It is added to the combustion chamber and reduces 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, check with a straight edge that the Toyota head and block faces are flat, and have any that need it resurfaced. Apply no gasket sealant: Cometic gaskets come already coated.

Technical guide

The construction offered

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

Choosing bore and thickness

Gasket bore. Cometic MLS comes in 87.5 mm (H0619SPH080S on the left, H0622SPH080S on the right), in 89 mm (C14151 on the left, C14152 on the right) and in 92.5 mm (C4137 on the left, C4136 on the right).

Thickness. Toyota discloses no thickness for the original gasket of this engine. 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 lower than the original, first measure with a dial gauge how far the pistons protrude above the Toyota block face: this figure gives the clearance that remains between piston and head.

The brand

Cometic Gasket, Inc. was founded in 1989 in Concord, Ohio; this US company designs gaskets and sealing solutions for engines. It became known for the made-to-measure gasket, cut to the bore and thickness required. All its manufacturing stays in the United States, using 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 Toyota does not disclose 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: 11115-50020

Important: the part numbers on this page match the Toyota 1UZ-FE engine: read the engine code of your vehicle, then check the bore, before you order.

Why switch to a reinforced gasket?

When the original gasket is no longer enough, the reinforced V8 gasket steps in: under higher combustion pressure it keeps its shape and is not crushed.

As soon as a turbo, a supercharger or a higher compression ratio comes into play, the Toyota head takes more load and the gasket becomes the most exposed part of the top end. A reinforced gasket stops gas or coolant leaks, and the head removal that would follow.