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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 multilayer MLS for the Mercedes-Benz 7.3-litre V12 engine, one part number per cylinder bank.
The V12 petrol engine of 7.3 litres with 48 valves, the Mercedes-Benz M120.AMG, powers the SL 73 AMG (R129), and the M297 the Pagani Zonda, in the version detailed below; the Cometic part numbers on this page are announced by the maker for the M120.AMG and M297.
Mercedes-Benz publishes neither the part number of the original gasket of these engines, nor its bore, nor its thickness, nor its construction. Each bank of six 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.
The head gasket does not seal on its own: the fasteners that press the Mercedes 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 V12 needs two different gaskets, one per bank: C4503 for the right bank and C4504 for the left bank. They come in a 91.5 mm bore, 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.
| Gasket bore | Thickness | Gasket volume | Gasket type OEM not specified | Brand | Part number |
| 91.5 mm | 0.69 mm | 4.54 | MLS | Cometic | C4503-027 |
| 91.5 mm | 0.69 mm | 4.54 | MLS | Cometic | C4504-027 |
| 91.5 mm | 0.76 mm | 5.00 | MLS | Cometic | C4503-030 |
| 91.5 mm | 0.76 mm | 5.00 | MLS | Cometic | C4504-030 |
| 91.5 mm | 0.91 mm | 5.98 | MLS | Cometic | C4503-036 |
| 91.5 mm | 0.91 mm | 5.98 | MLS | Cometic | C4504-036 |
| 91.5 mm | 1.02 mm | 6.71 | MLS | Cometic | C4503-040 |
| 91.5 mm | 1.02 mm | 6.71 | MLS | Cometic | C4504-040 |
| 91.5 mm | 1.14 mm | 7.50 | MLS | Cometic | C4503-045 |
| 91.5 mm | 1.14 mm | 7.50 | MLS | Cometic | C4504-045 |
| 91.5 mm | 1.30 mm | 8.55 | MLS | Cometic | C4503-051 |
| 91.5 mm | 1.30 mm | 8.55 | MLS | Cometic | C4504-051 |
| 91.5 mm | 1.42 mm | 9.34 | MLS | Cometic | C4503-056 |
| 91.5 mm | 1.42 mm | 9.34 | MLS | Cometic | C4504-056 |
| 91.5 mm | 1.52 mm | 9.99 | MLS | Cometic | C4503-060 |
| 91.5 mm | 1.52 mm | 9.99 | MLS | Cometic | C4504-060 |
| 91.5 mm | 1.68 mm | 11.05 | MLS | Cometic | C4503-066 |
| 91.5 mm | 1.68 mm | 11.05 | MLS | Cometic | C4504-066 |
| 91.5 mm | 1.78 mm | 11.70 | MLS | Cometic | C4503-070 |
| 91.5 mm | 1.78 mm | 11.70 | MLS | Cometic | C4504-070 |
| 91.5 mm | 1.91 mm | 12.56 | MLS | Cometic | C4503-075 |
| 91.5 mm | 1.91 mm | 12.56 | MLS | Cometic | C4504-075 |
| 91.5 mm | 2.03 mm | 13.35 | MLS | Cometic | C4503-080 |
| 91.5 mm | 2.03 mm | 13.35 | MLS | Cometic | C4504-080 |
| 91.5 mm | 2.13 mm | 14.01 | MLS | Cometic | C4503-084 |
| 91.5 mm | 2.13 mm | 14.01 | MLS | Cometic | C4504-084 |
| 91.5 mm | 2.18 mm | 14.33 | MLS | Cometic | C4503-086 |
| 91.5 mm | 2.18 mm | 14.33 | MLS | Cometic | C4504-086 |
| 91.5 mm | 2.34 mm | 15.39 | MLS | Cometic | C4503-092 |
| 91.5 mm | 2.34 mm | 15.39 | MLS | Cometic | C4504-092 |
| 91.5 mm | 2.49 mm | 16.37 | MLS | Cometic | C4503-098 |
| 91.5 mm | 2.49 mm | 16.37 | MLS | Cometic | C4504-098 |
| 91.5 mm | 3.05 mm | 20.06 | MLS | Cometic | C4503-120 |
| 91.5 mm | 3.05 mm | 20.06 | MLS | Cometic | C4504-120 |
| 91.5 mm | 3.56 mm | 23.41 | MLS | Cometic | C4503-140 |
| 91.5 mm | 3.56 mm | 23.41 | MLS | Cometic | C4504-140 |
The gasket volume is the empty space it leaves above each Mercedes 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.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts | M120.AMG, M297 | not published by the manufacturer |
Before fitting, check with a straight edge that the Mercedes head and block faces are flat, and have any that need it resurfaced. Apply no gasket sealant: Cometic gaskets come already coated.
 | MLS Cometic Stainless steel layers, stamped and joined by rivets. The outer layers carry active beads around each Mercedes 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. |
Gasket bore. Cometic MLS comes in 91.5 mm: C4503 for the right bank and C4504 for the left bank.
Thickness. Mercedes-Benz 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.
| Your goal | Thickness to choose |
| Keep the original compression ratio | Original thickness unknown: take the measurement of the removed standard gasket and keep the nearest value offered |
| Skimmed cylinder head, make up the lost height | The offered value closest to the figure taken on the removed standard gasket, plus the thickness taken off when resurfacing |
| Forced induction build, lower the ratio | A thickness above the one measured on the removed standard gasket |
| Naturally aspirated build, raise the ratio | A thickness thinner than that of the removed standard gasket, down to 0.69 mm, the lowest of the range |
If you choose a thickness lower than the original, first measure with a dial gauge how far the pistons protrude above the Mercedes block face: this figure gives the clearance that remains between piston and head.
 | Cometic Gasket, Inc., founded in 1989 in Concord, Ohio, is a US company that 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. |
| Criterion | Original gasket: part number not published | Reinforced gaskets |
| Construction | Construction not stated by the manufacturer | Multi-layer stainless steel (MLS) |
| Gasket bore | not published | 91,5 mm |
| Thicknesses available | thickness not published by the manufacturer | 0.69 to 3.56 mm, 18 values |
| Compression ratio adjustment | None | Through the thickness chosen |
| Resistance to overpressure | Limited to standard output | Designed for forced induction |
| Brand | Model | Engine code | Power | Years |
| Mercedes-Benz | SL (R129) 73 AMG (129.076) | M 120.AMG | 525 hp | 1999-2001 |
OEM part number: part number not published by the manufacturer.
Important: the part numbers on this page match the Mercedes-Benz M120.AMG and M297 engines: read the engine code of your vehicle, then check the bore, before you order.
When the original gasket is no longer enough, the reinforced V12 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 Mercedes 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.
