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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 6.0-litre V12 engine, one part number per cylinder bank.
Mercedes-Benz's 6.0-litre twelve-cylinder V engine, known as the M120 and offered as the M120.980, M120.981, M120.982 and M120.983, powers the S-Class (W140) 600 SE and 600 SEL, the SEC and CL 600 coupés (C140) and the SL 600 (R129) in the table below. The engine has two heads: one gasket is needed per cylinder bank, so two per engine, a right-hand and a left-hand.
The manufacturer part number of the standard gasket is 120 016 20 20; neither the bore, nor the thickness, nor the construction appears in any manufacturer documentation. The standard gasket is sized for the original combustion pressure: beyond it, the clamping load fades, the head lifts and coolant passes into a cylinder.
The gasket alone does not provide the seal: the fasteners that clamp the head to the block count as much as it does. Beyond 100 N/mm², a composite gasket settles for good; the 301 stainless steel of the MLS carries 517 N/mm², 5 times more, and springs back to shape with every combustion. The raised features of the outer plates pass on the clamping load around each cylinder and each fluid passage, without any machining of the block.
This page gathers the part numbers of a single racing manufacturer, Cometic, in multi-layer MLS construction, with a 90 mm gasket bore in two versions, one per cylinder bank. Thicknesses run from 0.686 to 3.556 mm, enough to adjust the compression ratio without altering either the pistons or the heads. 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 OEM 120 016 20 20 |
| 90 mm | 0.69 mm | 4.39 | MLS right bank | Cometic | C4500-027 |
| 90 mm | 0.69 mm | 4.39 | MLS left bank | Cometic | C4501-027 |
| 90 mm | 0.76 mm | 4.83 | MLS right bank | Cometic | C4500-030 |
| 90 mm | 0.76 mm | 4.83 | MLS left bank | Cometic | C4501-030 |
| 90 mm | 0.91 mm | 5.79 | MLS right bank | Cometic | C4500-036 |
| 90 mm | 0.91 mm | 5.79 | MLS left bank | Cometic | C4501-036 |
| 90 mm | 1.02 mm | 6.49 | MLS right bank | Cometic | C4500-040 |
| 90 mm | 1.02 mm | 6.49 | MLS left bank | Cometic | C4501-040 |
| 90 mm | 1.14 mm | 7.25 | MLS right bank | Cometic | C4500-045 |
| 90 mm | 1.14 mm | 7.25 | MLS left bank | Cometic | C4501-045 |
| 90 mm | 1.30 mm | 8.27 | MLS right bank | Cometic | C4500-051 |
| 90 mm | 1.30 mm | 8.27 | MLS left bank | Cometic | C4501-051 |
| 90 mm | 1.42 mm | 9.03 | MLS right bank | Cometic | C4500-056 |
| 90 mm | 1.42 mm | 9.03 | MLS left bank | Cometic | C4501-056 |
| 90 mm | 1.52 mm | 9.67 | MLS right bank | Cometic | C4500-060 |
| 90 mm | 1.52 mm | 9.67 | MLS left bank | Cometic | C4501-060 |
| 90 mm | 1.68 mm | 10.69 | MLS right bank | Cometic | C4500-066 |
| 90 mm | 1.68 mm | 10.69 | MLS left bank | Cometic | C4501-066 |
| 90 mm | 1.78 mm | 11.32 | MLS right bank | Cometic | C4500-070 |
| 90 mm | 1.78 mm | 11.32 | MLS left bank | Cometic | C4501-070 |
| 90 mm | 1.91 mm | 12.15 | MLS right bank | Cometic | C4500-075 |
| 90 mm | 1.91 mm | 12.15 | MLS left bank | Cometic | C4501-075 |
| 90 mm | 2.03 mm | 12.91 | MLS right bank | Cometic | C4500-080 |
| 90 mm | 2.03 mm | 12.91 | MLS left bank | Cometic | C4501-080 |
| 90 mm | 2.13 mm | 13.55 | MLS right bank | Cometic | C4500-084 |
| 90 mm | 2.13 mm | 13.55 | MLS left bank | Cometic | C4501-084 |
| 90 mm | 2.18 mm | 13.87 | MLS right bank | Cometic | C4500-086 |
| 90 mm | 2.18 mm | 13.87 | MLS left bank | Cometic | C4501-086 |
| 90 mm | 2.34 mm | 14.89 | MLS right bank | Cometic | C4500-092 |
| 90 mm | 2.34 mm | 14.89 | MLS left bank | Cometic | C4501-092 |
| 90 mm | 2.49 mm | 15.84 | MLS right bank | Cometic | C4500-098 |
| 90 mm | 2.49 mm | 15.84 | MLS left bank | Cometic | C4501-098 |
| 90 mm | 3.05 mm | 19.40 | MLS right bank | Cometic | C4500-120 |
| 90 mm | 3.05 mm | 19.40 | MLS left bank | Cometic | C4501-120 |
| 90 mm | 3.56 mm | 22.65 | MLS right bank | Cometic | C4500-140 |
| 90 mm | 3.56 mm | 22.65 | MLS left bank | Cometic | C4501-140 |
Gasket volume is the space left free above each cylinder. It adds to the combustion chamber and lowers the compression ratio by the same amount. Restrict the comparison to gaskets of the same bore.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts | M120.980, M120.981, M120.982, M120.983, M297 | not published by the manufacturer |
Before refitting, run a straight edge over the head and the block to check their flatness, and have the surface that needs it resurfaced. Add no sealing paste: Cometic gaskets are supplied already coated.
 | Cometic MLS Stamped stainless steel plates, stacked on one another and riveted. The outer plates show active beads around each cylinder and each liquid passage. The gasket seals with a moderate clamping load and barely distorts the bore. It is the do-it-all solution, from the tuned naturally aspirated engine to sensible boost. |
Gasket bore. The Cometic MLS comes in 90 mm for the right bank (C4500) and for the left bank (C4501). The part numbers cover the M120 of 6.0 litres and the M297 of 6.9 and 7.0 litres.
Thickness. No figure is supplied by the manufacturer for the standard gasket: only the reading of the gasket you remove counts. 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 | Standard thickness not on record: measure the gasket you remove, then use the closest figure between 0.686 and 3.556 mm |
| Skimmed cylinder head, make up the lost height | From 0.686 to 3.556 mm, use the thickness of the removed gasket plus the material the resurfacing took off |
| Forced induction build, lower the ratio | 3.556 mm, if the removed gasket is thinner |
| Naturally aspirated build, raise the ratio | 0.686 mm, if the removed gasket is thicker |
When no original thickness is published, use a dial gauge to measure how far the pistons protrude above the block deck: that gives the clearance remaining between piston and head, particularly with the thinnest gasket.
 | Cometic Gasket, Inc., a company from the United States founded in 1989 in Concord, Ohio, designs engine gaskets and sealing solutions. It has made a speciality of the custom gasket, at the bore and thickness requested, built entirely in the United States from American materials. |
| Criterion | Original gasket 120 016 20 20 | Reinforced gaskets |
| Construction | Not specified by the manufacturer | Multi-layer stainless steel, or steel and aramid fibre with a stainless ring |
| Gasket bore | not published by the manufacturer | 90 mm |
| Thicknesses available | not published by the manufacturer | 0.686 to 3.556 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 | CLASSE S (W140) 600 SE, SEL, S 600 (140.056, 140.057) | M120.980, M120.982 | 394 and 408 hp | 04.1991 - 10.1998 |
| Mercedes-Benz | CLASSE S Coupé (C140) SEC, CL 600 (140.076) | M120.980, M120.982 | 367, 394 and 408 hp | 07.1992 - 02.1999 |
| Mercedes-Benz | SL (R129) 600, 600 SL (129.076) | M120.981, M120.983 | 394 and 408 hp | 02.1992 - 10.2001 |
OEM part number: 120 016 20 20.
Important: the gaskets on this page are listed for the M120.980, M120.981, M120.982 and M120.983 engines in the survey below and, according to the manufacturer, for the M297 too. For any other vehicle, find the engine code first before placing an order.
When the standard gasket is no longer enough, the reinforced one takes over: at higher combustion pressure it holds its geometry rather than sagging.
Ask an engine for still more, with extra boost, a higher compression ratio or a thorough build, and the head gasket is the first part in the top end to give up. A reinforced gasket spares you the leak and the cylinder head removal that goes with it, a job that costs far more than the part itself.
