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2.0L 24v - M50B20
Manufacturers
2.0L 24v - M50B20
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Reinforced Cometic head gasket, in MLS. Sold individually.
The BMW M50B20 is the 2.0 litre 24-valve inline six-cylinder petrol engine fitted to the 320i (E36) saloon, Coupé and Convertible, and to the 520i (E34) saloon and Touring. Its bore is 80 mm with a 66 mm stroke, and its VANOS variable valve timing version, the M50B20TU, is covered by the same Cometic part numbers.
This original gasket carries the part number 11 12 1 726 625, which replaces 11 12 1 726 623. It is an asbestos-free metal and fibre composite, with an 81 mm bore and a thickness of 1.74 mm. BMW offers a single repair size, 11 12 1 726 628 in 2.05 mm, intended for skimmed cylinder heads. It is sized for standard combustion pressure and settles as soon as that pressure rises: clamping load drops, the cylinder head lifts, and coolant enters a cylinder.
Sealing does not come from the head gasket alone: it keeps the seal because the fasteners hold the cylinder head pressed onto the block. Past 100 N/mm² of admissible stress, the original composite is crushed for good, whereas the 301 stainless steel of the MLS gaskets takes 517 N/mm², 5 times more than the original, and recovers its shape at every combustion.
This page brings together the part numbers from Cometic, a racing manufacturer, in MLS multi-layer steel construction. The gasket has an 82 mm bore, against 81 mm for the original, and comes in 16 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, one gasket per engine.
| Gasket bore OEM 81 mm | Thickness OEM 1.74 mm | Gasket volume OEM 8.97 cm³ | Gasket type OEM composite | Brand | Part number OEM 11 12 1 726 625 |
| 82 mm | 0.69 mm | 3.64 | MLS | Cometic | C4332-027 |
| 82 mm | 0.76 mm | 4.01 | MLS | Cometic | C4332-030 |
| 82 mm | 0.91 mm | 4.81 | MLS | Cometic | C4332-036 |
| 82 mm | 1.02 mm | 5.39 | MLS | Cometic | C4332-040 |
| 82 mm | 1.14 mm | 6.02 | MLS | Cometic | C4332-045 |
| 82 mm | 1.30 mm | 6.87 | MLS | Cometic | C4332-051 |
| 82 mm | 1.42 mm | 7.50 | MLS | Cometic | C4332-056 |
| 82 mm | 1.52 mm | 8.03 | MLS | Cometic | C4332-060 |
| 82 mm | 1.68 mm | 8.87 | MLS | Cometic | C4332-066 |
| 82 mm | 1.78 mm | 9.40 | MLS | Cometic | C4332-070 |
| 82 mm | 2.03 mm | 10.72 | MLS | Cometic | C4332-080 |
| 82 mm | 2.18 mm | 11.51 | MLS | Cometic | C4332-086 |
| 82 mm | 2.34 mm | 12.36 | MLS | Cometic | C4332-092 |
| 82 mm | 2.49 mm | 13.15 | MLS | Cometic | C4332-098 |
| 82 mm | 3.05 mm | 16.11 | MLS | Cometic | C4332-120 |
| 82 mm | 3.56 mm | 18.80 | MLS | Cometic | C4332-140 |
Gasket volume: the free volume the gasket creates above each cylinder. It enlarges the combustion chamber, and the higher it is, the further the compression ratio drops. These figures are only compared with one another at an identical gasket bore.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts 11 12 1 721 938, M10 x 95 | M50B20 | 30 Nm, then 90°, then 90° |
Before fitting, check the flatness of the cylinder head and of the block with a straight edge and have them skimmed if necessary. These gaskets require no sealant: Cometic supplies them already coated.
| Reinforced ARP cylinder head studs M50B20 → |
 | Cometic MLS A gasket made of several stainless steel layers, stamped one by one and then riveted together. Each cylinder and each fluid passage is surrounded, on the outer layers, by active beads. It seals under a moderate clamping load while limiting bore distortion. It is the solution that suits the widest range of builds, from a tuned naturally aspirated engine to light forced induction. |
Gasket bore. The Cometic MLS comes in 82 mm.
Thickness. The original gasket is 1.74 mm thick. 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 | 1.78 mm, the value closest to the original 1.74 mm |
| Skimmed cylinder head, make up the lost height | 1.78 mm + what was removed |
| Forced induction build, lower the ratio | A thickness above 1.78 mm |
| Naturally aspirated build, raise the ratio | A thickness below 1.78 mm |
For any thickness below the original, check with a dial gauge how far your pistons rise above the block: that is what sets the remaining clearance between piston and cylinder head once the engine is rebuilt.
 | Cometic Gasket, Inc. is an American company that has been making engine gaskets and sealing solutions since it was founded in 1989 in Concord, Ohio. Its know-how lies in the gasket made on request, to the bore and thickness you want. The whole of its product range is manufactured in the United States, in American materials. |
| Criterion | Original gasket 11 12 1 726 625 | Reinforced gaskets |
| Construction | Asbestos-free metal and fibre composite | Multi-layer stainless steel |
| Gasket bore | 81 mm | 82 mm |
| Thicknesses available | 1.74 mm, 2.05 mm in repair size | 0.69 to 3.56 mm, 16 values |
| Compression ratio adjustment | None | Through the thickness chosen |
| Resistance to overpressure | Limited to standard output | Designed for forced induction |
| Model | Engine code | Power | Years |
| 320i (E36) | M50B20 / M50B20TU | 150 hp | 1991-1995 |
| 320i Coupé (E36) | M50B20 / M50B20TU | 150 hp | 1991-1995 |
| 320i Cabriolet (E36) | M50B20 / M50B20TU | 150 hp | 1993-1995 |
| 520i 24V (E34) | M50B20 / M50B20TU | 150 hp | 1990-1995 |
| 520i Touring (E34) | M50B20 / M50B20TU | 150 hp | 1991-1996 |
OEM part number: 11 12 1 726 625 in standard size, 11 12 1 726 628 in repair size.
Important: the M52B20, fitted to part of the 320i (E36) range, is not covered by this page: 320i E36 models with the M52B20 engine are excluded, as are the M50B25 and M52, which receive another original cylinder head gasket, part numbers 11 12 1 726 619 and 11 12 1 726 622.
The reinforced gasket stands firm where the original one reaches its limits: faced with higher combustion pressure, it keeps its shape and does not crush.
A turbo conversion, a supercharger or a higher compression ratio: each time power goes up, the head gasket becomes the most stressed part of the top end, and so the weakest. Fitting a reinforced gasket is then no luxury but a safety measure, since it prevents the failure and the cylinder head removal that follows.
