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BY REFERENCE COMETIC - Reinforced cylinder head gaskets
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BY REFERENCE COMETIC - Reinforced cylinder head gaskets
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Reinforced Cometic head gasket in MLS. One gasket per engine: choose the bore and thickness you want.
The K20Z3 is a 2.0 litre (1998 cc) petrol engine with four in-line cylinders and 16 valves. It powers the Acura CSX and the Honda Civic VIII (FD, FA) saloon listed below.
The original gaskets carry the part numbers 12251-RAC-003, 12251-RAC-004, 12251-RBB-004 and 12251-RBC-004. Honda publishes neither their bore, their thickness nor their construction. This in-line four takes a single head gasket. Meant for the standard combustion pressure, it gives out once that pressure rises: the head loses clamping load, lifts and coolant reaches a cylinder.
Sealing does not depend on the gasket alone but also on the fasteners that press the head onto the block. A composite gasket settles for good beyond 100 N/mm²; the 301 stainless steel of MLS gaskets takes 517 N/mm², 5 times more, and recovers its shape at every combustion.
This page brings together 36 part numbers from Cometic, the American competition gasket maker, for a single construction: MLS, a multilayer steel design. Eighteen gaskets (C4561) have an 86 mm bore and eighteen (C4562) an 87 mm bore; thicknesses run 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, one gasket per engine.
| Gasket bore | Thickness | Gasket volume | Gasket type OEM not specified | Brand | Part number OEM 12251-RAC-003 ; 12251-RAC-004 ; 12251-RBB-004 ; 12251-RBC-004 |
| 86 mm | 0.69 mm | 4.01 | MLS | Cometic | C4561-027 |
| 86 mm | 0.76 mm | 4.41 | MLS | Cometic | C4561-030 |
| 86 mm | 0.91 mm | 5.29 | MLS | Cometic | C4561-036 |
| 86 mm | 1.02 mm | 5.92 | MLS | Cometic | C4561-040 |
| 86 mm | 1.14 mm | 6.62 | MLS | Cometic | C4561-045 |
| 86 mm | 1.30 mm | 7.55 | MLS | Cometic | C4561-051 |
| 86 mm | 1.42 mm | 8.25 | MLS | Cometic | C4561-056 |
| 86 mm | 1.52 mm | 8.83 | MLS | Cometic | C4561-060 |
| 86 mm | 1.68 mm | 9.76 | MLS | Cometic | C4561-066 |
| 86 mm | 1.78 mm | 10.34 | MLS | Cometic | C4561-070 |
| 86 mm | 1.91 mm | 11.09 | MLS | Cometic | C4561-075 |
| 86 mm | 2.03 mm | 11.79 | MLS | Cometic | C4561-080 |
| 86 mm | 2.13 mm | 12.37 | MLS | Cometic | C4561-084 |
| 86 mm | 2.18 mm | 12.66 | MLS | Cometic | C4561-086 |
| 86 mm | 2.34 mm | 13.59 | MLS | Cometic | C4561-092 |
| 86 mm | 2.49 mm | 14.46 | MLS | Cometic | C4561-098 |
| 86 mm | 3.05 mm | 17.72 | MLS | Cometic | C4561-120 |
| 86 mm | 3.56 mm | 20.68 | MLS | Cometic | C4561-140 |
| 87 mm | 0.69 mm | 4.10 | MLS | Cometic | C4562-027 |
| 87 mm | 0.76 mm | 4.52 | MLS | Cometic | C4562-030 |
| 87 mm | 0.91 mm | 5.41 | MLS | Cometic | C4562-036 |
| 87 mm | 1.02 mm | 6.06 | MLS | Cometic | C4562-040 |
| 87 mm | 1.14 mm | 6.78 | MLS | Cometic | C4562-045 |
| 87 mm | 1.30 mm | 7.73 | MLS | Cometic | C4562-051 |
| 87 mm | 1.42 mm | 8.44 | MLS | Cometic | C4562-056 |
| 87 mm | 1.52 mm | 9.04 | MLS | Cometic | C4562-060 |
| 87 mm | 1.68 mm | 9.99 | MLS | Cometic | C4562-066 |
| 87 mm | 1.78 mm | 10.58 | MLS | Cometic | C4562-070 |
| 87 mm | 1.91 mm | 11.35 | MLS | Cometic | C4562-075 |
| 87 mm | 2.03 mm | 12.07 | MLS | Cometic | C4562-080 |
| 87 mm | 2.13 mm | 12.66 | MLS | Cometic | C4562-084 |
| 87 mm | 2.18 mm | 12.96 | MLS | Cometic | C4562-086 |
| 87 mm | 2.34 mm | 13.91 | MLS | Cometic | C4562-092 |
| 87 mm | 2.49 mm | 14.80 | MLS | Cometic | C4562-098 |
| 87 mm | 3.05 mm | 18.13 | MLS | Cometic | C4562-120 |
| 87 mm | 3.56 mm | 21.16 | MLS | Cometic | C4562-140 |
The volume of a gasket is the free space it leaves above each cylinder; it adds to the combustion chamber and reduces the compression ratio. Compare it only at equal bore, here 86 mm for the C4561 and 87 mm for the C4562.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts | K20Z3 | not published by the manufacturer |
Before fitting, check the flatness of the head and the block with a straight edge and have them resurfaced if necessary. Cometic supplies these gaskets already coated: apply no sealant.
 | Cometic MLS Several stainless steel sheets, embossed and assembled by rivets. The outer sheets show active beads that surround each cylinder and each fluid passage. Moderate clamping is enough to seal and the bore distorts little: a versatile construction, from the tuned naturally aspirated engine to moderate boost. |
Gasket bore. The Cometic MLS is offered in 86 mm (C4561) and in 87 mm (C4562).
Thickness. No thickness is published for the original gaskets 12251-RAC-003, 12251-RAC-004, 12251-RBB-004 and 12251-RBC-004. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.
| Your goal | Thickness to choose |
| Keep the original compression ratio | Original thickness not published: take the dimension of the removed gasket and pick the offered value that comes closest |
| Skimmed cylinder head, make up the lost height | The offered value closest to the dimension of the removed gasket, plus the metal taken off at resurfacing |
| Forced induction build, lower the ratio | A thickness above the dimension of the removed gasket |
| Naturally aspirated build, raise the ratio | A thickness below the dimension of the removed gasket, down to 0.69 mm, the lowest value offered |
If you go below the original thickness, first read with a dial gauge the height the pistons stand proud of the block's gasket face: that figure sets the clearance that remains between piston and head.
 | Cometic Gasket, Inc. is an American company founded in 1989 in Concord, Ohio, that designs and produces engine gaskets and sealing elements. It is known for the custom gasket, cut to the bore and thickness requested, made in the United States from American raw materials. |
| Criterion | Original gaskets (four part numbers) | Reinforced gaskets |
| Construction | Construction not stated by the manufacturer | Multilayer stainless steel (MLS) |
| Gasket bore | not published | 86 mm and 87 mm |
| Thicknesses available | thickness not provided by the manufacturer | 0.69 to 3.56 mm, 18 values per bore |
| Compression ratio adjustment | None | Through the thickness chosen |
| Resistance to overpressure | Limited to standard output | Designed for forced induction |
| Model | Engine code | Power | Years |
| Acura CSX Berline tricorps 2.0 | K20Z3 | 200 hp | 2006-2010 |
| Honda Civic VIII Berline tricorps (FD, FA) 2.0 | K20Z3 | 192 hp | 2008-2011 |
| Honda Civic VIII Berline tricorps (FD, FA) 2.0 (FD2) | K20Z3 | 200 hp | 2007-2011 |
OEM part number: 12251-RAC-003, 12251-RAC-004, 12251-RBB-004 and 12251-RBC-004.
Important: the part numbers on this page suit only the K20Z3 engine: check your vehicle's engine code before ordering.
The reinforced gasket relays the original one when that has reached its limit: under stronger combustion pressure it keeps its shape instead of settling.
When the engine is built up further, with livelier camshafts, a raised compression ratio or added boost, the head gasket gives way before the rest of the top end. A reinforced gasket avoids the leak, then the head removal, which costs far more than the part.
