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3.0L 12v - M30B30
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3.0L 12v - M30B30
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Reinforced Cometic head gasket, in MLS. Sold individually, one gasket per engine.
The BMW M30B30 and M30B32 are naturally aspirated twelve-valve inline-six petrol engines, of 3.0 litres for the M30B30 and 3.2 litres for the M30B32. The bore is 89 mm on both, with a stroke of 80 mm for the M30B30 and 86 mm for the M30B32. They are fitted to the BMW E3, E9, E12, E23, E24, E28, E32 and E34 models listed below.
This original gasket carries the part number 11 12 9 065 638, replaced by 11 12 9 065 648. BMW lists it as an asbestos-free cylinder head gasket without specifying its construction; its bore is 91 mm and its thickness 1.80 mm in the standard size, 2.10 mm in the repair size (+0.30 mm). The engine takes only one. It is intended for standard combustion pressure: as that pressure rises, clamping load fades, the cylinder head lifts and coolant passes into a cylinder.
A head gasket does not seal by itself: it holds thanks to the fasteners, which press the head onto the block. A composite gasket ends up crushed for good beyond 100 N/mm² of admissible stress, whereas the 301 stainless steel of MLS gaskets withstands 517 N/mm², 5 times more, and regains its shape at every combustion.
This page gathers the part numbers of Cometic, an American maker of racing gaskets, in a single construction: the multi-layer steel MLS. Every gasket has a 90 mm bore, 1 mm more than the 89 mm engine bore, and 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 OEM 91 mm | Thickness OEM 1.80 mm | Gasket volume OEM 11.71 cm³ | Gasket type OEM not specified | Brand | Part number OEM 11 12 9 065 638 |
| 90 mm | 0.69 mm | 4.39 | MLS | Cometic | C4476-027 |
| 90 mm | 0.76 mm | 4.83 | MLS | Cometic | C4476-030 |
| 90 mm | 0.91 mm | 5.79 | MLS | Cometic | C4476-036 |
| 90 mm | 1.02 mm | 6.49 | MLS | Cometic | C4476-040 |
| 90 mm | 1.14 mm | 7.25 | MLS | Cometic | C4476-045 |
| 90 mm | 1.30 mm | 8.27 | MLS | Cometic | C4476-051 |
| 90 mm | 1.42 mm | 9.03 | MLS | Cometic | C4476-056 |
| 90 mm | 1.52 mm | 9.67 | MLS | Cometic | C4476-060 |
| 90 mm | 1.68 mm | 10.69 | MLS | Cometic | C4476-066 |
| 90 mm | 1.78 mm | 11.32 | MLS | Cometic | C4476-070 |
| 90 mm | 1.91 mm | 12.15 | MLS | Cometic | C4476-075 |
| 90 mm | 2.03 mm | 12.91 | MLS | Cometic | C4476-080 |
| 90 mm | 2.18 mm | 13.87 | MLS | Cometic | C4476-086 |
| 90 mm | 2.34 mm | 14.89 | MLS | Cometic | C4476-092 |
| 90 mm | 2.49 mm | 15.84 | MLS | Cometic | C4476-098 |
| 90 mm | 3.05 mm | 19.40 | MLS | Cometic | C4476-120 |
| 90 mm | 3.56 mm | 22.65 | MLS | Cometic | C4476-140 |
Gasket volume is the free space the gasket leaves above each cylinder. It adds to the combustion chamber: the larger it is, the lower the compression ratio. Only compare gaskets of the same bore.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts 11 12 0 621 144, M12 x 156 | M30B30, M30B32 | 60 Nm, wait 20 min, 80 Nm, hot engine 25 min, then 35° (new bolts, washed and oiled; current TIS procedure) |
Before fitting, check the flatness of the cylinder head and the block with a straight edge, and have them machined if necessary. These gaskets are fitted without sealant, as Cometic supplies them already coated.
| Reinforced ARP cylinder head studs BMW M30 → |
 | Cometic MLS A stack of stamped stainless steel layers riveted together. The outer layers carry active beads around each cylinder and each fluid passage. A moderate clamping load is enough to seal, and the bore distorts little. It is the versatile solution, from the tuned naturally aspirated engine to moderate boost. |
Gasket bore. The Cometic MLS comes in 90 mm (C4476), and in that bore only.
Thickness. The original gasket is 1.80 mm thick in the standard size and 2.10 mm in the repair size (+0.30 mm). The 730i of the E32 generation takes an original gasket of 1.72 mm. 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 or 1.91 mm, the two values closest to the original 1.80 mm |
| Skimmed cylinder head, make up the lost height | 1.78 mm or 1.91 mm + what was removed |
| Forced induction build, lower the ratio | A thickness above 1.91 mm |
| Naturally aspirated build, raise the ratio | A thickness below 1.78 mm, down to 0.69 mm, the thinnest offered |
With a thickness below the original, measure with a dial gauge how far your pistons stand above the block: it sets the clearance left between piston and head.
 | Cometic Gasket, Inc. was founded in 1989 in Concord, Ohio. This American manufacturer produces gaskets and sealing solutions for engines, with one speciality: the gasket made to order, in the bore and thickness wanted. All manufacturing stays in the United States, with American materials. |
| Criterion | Original gasket 11 12 9 065 638 | Reinforced gaskets |
| Construction | Construction not stated by the manufacturer | Multi-layer stainless steel (MLS) |
| Gasket bore | 91 mm | 90 mm |
| Thicknesses available | 1.80 mm, 2.10 mm in the repair size | 0.69 to 3.56 mm, 17 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 |
| 3.0 S, 3.0 L, 3.0 Si, 3.0 Bavaria (E3) | M30B30 | 179, 180, 194 and 200 hp | 1971-1977 |
| 3.2 Li (E3) | M30B32 | 200 hp | 1975-1977 |
| 3.0 CS, 3.0 CSi (E9) | M30B30 | 180, 193 and 200 hp | 1970-1976 |
| 530 i (E12) | M30B30 | 178 hp | 1974-1978 |
| 630 CS, 630 CSi (E24) | M30B30 | 178, 184 and 185 hp | 1976-1979 |
| 633 CSi (E24) | M30B32 | 179, 184, 197 and 200 hp | 1975-1984 |
| 730 (E23) | M30B30 | 184 hp | 1977-1979 |
| 732 i, 733 i (E23) | M30B32 | 177, 179, 184 and 197 hp | 1977-1986 |
| 533 i (E28) | M30B32 | 184 hp | 1982-1984 |
| 730 i, 730 iL (E32) | M30B30 | 188 and 197 hp | 1985-1994 |
| 530 i (E34) | M30B30 | 188 hp | 1988-1990 |
OEM part number: 11 12 9 065 638, replaced by 11 12 9 065 648.
Important: the part numbers on this page fit only the M30B30 and M30B32 engines: check your vehicle's engine code before ordering.
When the original gasket reaches its limit, the reinforced one still holds: under higher combustion pressure it keeps its shape instead of being crushed.
When power increases, through a supercharger, a turbo or a raised compression ratio, the head gasket is the first part to give way in the top end. Choosing a reinforced gasket is therefore about reliability rather than comfort: it avoids the breakdown and the cylinder head removal that follows.
