Reinforced head gasket Nissan QR25DE

The Nissan engines covered

The 2.5-litre QR25DE petrol engine, a four-cylinder, powers many Nissan models, from the Altima to the X-Trail, listed below.

The original gasket carries part number 11044-6N201. Nissan does not publish its bore, thickness or construction. It is sized for the standard combustion pressure: when that pressure climbs, the clamping load relaxes, the cylinder head moves away from the block and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

The gasket does not close the circuit on its own: the fasteners that pull the head onto the block provide half of it. Beyond 100 N/mm² of stress, a composite gasket sags for good; the 301 stainless steel of MLS gaskets withstands up to 517 N/mm², 5 times more, and springs back with every combustion.

This page brings together three Cometic part numbers, from an American maker of competition gaskets, all in MLS construction: C4614, C4615 and C4616. Bore of 90 mm, thicknesses from 0.69 to 1.42 mm depending on the part number. As a rule, the gasket bore exceeds the cylinder bore by at least 0.5 mm. Each part number is sold individually, one gasket per engine.

Technical specifications

A gasket's volume is the empty space it leaves above each cylinder. It adds to the combustion chamber and lowers the compression ratio; only compare gaskets of the same bore.

Preparation and fitting

Before fitting the gasket, run a straightedge over the cylinder head and the block, and have any warped surface machined. Cometic supplies this gasket already coated: do not add any sealing paste.

Technical guide

The construction offered

MLS Cometic Embossed stainless steel sheets, stacked and riveted together. The outer sheets carry active beads around every cylinder and every fluid passage. A moderate tightening torque is enough to seal, and the bore moves very little. An all-round gasket, from the tuned naturally aspirated engine to moderate forced induction.

Choosing bore and thickness

Gasket bore. The Cometic MLS gasket is available in 90 mm (C4614, C4615 and C4616), with no other bore.

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

Since the original thickness is not published, measure with a dial gauge how far the pistons stand proud of the block face, especially if the removed gasket is thinner than the target thickness: that reading gives the true clearance between piston and cylinder head.

The brand

Cometic Gasket, Inc., an American maker of gaskets and sealing parts for engines, was founded in 1989 in Concord, Ohio. Its reputation rests on the made-to-measure gasket, cut to the bore and thickness requested, and on production that is entirely American, from domestic 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 90 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: 11044-6N201.

Important: the part numbers on this page fit the QR25DE engine: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket reaches its limit, the reinforced gasket takes over: under higher combustion pressure it resists crushing and keeps its shape.

Adding a turbo or a supercharger, or raising the compression ratio, puts the head gasket to the test first, the weak link of the top end. A reinforced gasket avoids the leak and the cylinder head removal that follows, a job far more costly than the gasket itself.