Reinforced head gasket Honda 2.0 B20B B20B4 B20Z1 B20Z2

The Honda engines covered

The B20B, B20Z1, B20B4 and B20Z2 are 2.0 litre petrol engines. They power the Honda CR-V I (RD), Orthia / Partner, SMX and Stepwgn models listed in the compatibility table below.

The original gasket carries part number 12251-P3F-005. Honda publishes neither its bore, nor its thickness, nor its construction. An engine takes a single cylinder head gasket. It is sized for standard combustion pressure; when that rises, the clamping load eases, the head lifts slightly and coolant enters a cylinder.

Reinforced cylinder head gaskets

Sealing does not rest on the gasket alone but also on the fasteners that press the head onto the block. Beyond 100 N/mm², a composite gasket compresses for good; the 301 stainless steel of MLS gaskets takes 517 N/mm², 5 times more, and recovers its shape at every combustion. This applies to the B20B, B20Z1, B20B4 and B20Z2.

This page brings together nineteen part numbers from two competition makers, Athena (Italy) and Cometic (United States), all in MLS construction, multi-layer steel, with an 85 mm bore. Athena offers one part number, in 0.85 mm (338104R); Cometic offers eighteen, the C4250 range, from 0.69 to 3.56 mm. The engine takes only one gasket: order a single part number, according to the thickness you want. The thicknesses offered let you 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 above each cylinder: it adds to the combustion chamber and lowers the compression ratio. All the part numbers on this page share the same 85 mm bore, so they can be compared with one another.

Preparation and fitting

Before reassembly, check the flatness of the head and block mating faces with a straightedge and have them resurfaced if needed. Cometic gaskets arrive already coated: do not apply any sealing paste. This applies to the B20B, B20Z1, B20B4 and B20Z2.

Technical guide

The two constructions offered

Athena MLS Athena MLS Between two and five AISI 301 stainless steel sheets, laser cut, stamped and riveted. A folded sheet rings each cylinder: this Gas Stopper sends the clamping load back toward the combustion chamber, while beads close off the water and oil circuits. Each outer face receives a coating: one layer withstands high temperatures and fills small flaws in the block and head, a silicone layer keeps the gasket from sticking at removal. It is Athena's all-steel formula, suited from the prepared naturally aspirated engine to moderate forced induction. This applies to the B20B, B20Z1, B20B4 and B20Z2.

Cometic MLS Several stainless steel sheets, stamped and riveted together. Each outer sheet carries active beads tracing the outline of every cylinder and fluid passage. A moderate clamping load is enough to seal, and the bore distorts very little. This versatile gasket suits anything from a tuned naturally aspirated engine to light boost. Cometic offers it here in eighteen thicknesses, from 0.69 to 3.56 mm.

Choosing bore and thickness

Gasket bore. The Athena MLS (338104R) and the Cometic MLS (C4250) are both offered here in 85 mm.

Thickness. No thickness is published for the original gasket 12251-P3F-005. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

Before choosing a thickness below the original, use a dial gauge to read how far the pistons stand proud of the block face: it sets the clearance that remains between piston and head.

The two brands

	Athena S.p.A. is an Italian maker of gaskets and engine components. Its head office and main plant are in Alonte, in the Veneto region, and the group also has sites in Spain, the United States, Brazil and India. Its multi-layer gaskets fit certain car makers as original equipment, and its competition range is entirely designed and made in Italy. Part number 338104R on this page comes from it.
	Cometic Gasket, Inc. is an American company founded in 1989 and based in Concord, Ohio, which designs and builds gaskets and sealing parts for engines. It earned its name with made-to-measure gaskets, cut to the bore and thickness required, all made in the United States from American materials. The C4250 range on this page is made by the company.

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 85 mm bore of these gaskets 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: 12251-P3F-005.

Important: the part numbers on this page suit only the B20B, B20Z1, B20B4 and B20Z2 engines: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket is no longer enough, the reinforced gasket replaces it: under higher combustion pressure it keeps its shape instead of collapsing. This applies to the B20B, B20Z1, B20B4 and B20Z2.

Whether you add a turbo, raise the compression ratio or rev higher with livelier cams, the cylinder head gasket becomes the weak link of a high-output engine. A reinforced gasket prevents the leak and the head removal that goes with it, far costlier than the gasket. This applies to the B20B, B20Z1, B20B4 and B20Z2.