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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 CFM-20, for the Colombo V12 of the Ferrari 250 Europa, 250 GT and 250 LM.
The Ferrari Colombo V12, identified by the code "F250", powers the Ferrari 250 Europa, 250 GT and 250 LM detailed below.
The maker of the Colombo V12 publishes neither the part number, nor the bore, nor the construction, nor the thickness of the original gasket. This gasket is sized for standard combustion pressure: when that pressure rises, the head loses clamping force, lifts and lets coolant reach a cylinder.
The gasket does not guarantee the seal on its own: the fasteners that clamp the head onto the block weigh just as much. CFM-20 combines a galvanized steel core with a soft asbestos-free compound that makes up for small irregularities in the gasket faces. On these Ferraris, torquing in several passes keeps the pressure even.
This page offers the part numbers from the American maker Cometic, a specialist in racing gaskets, in a single construction: CFM-20. Their bore is 75.5 mm or 75 mm and their thickness 1.09 mm or 1.50 mm. Each part number is sold individually.
| Gasket bore | Thickness | Gasket volume | Gasket type OEM not specified | Brand | Part number |
| 75 mm | 1.50 mm | 6.63 | CFM-20 | Cometic | C14109-059 |
| 75.5 mm | 1.09 mm | 4.88 | CFM-20 | Cometic | C14101-043 |
A gasket's volume is the space it leaves free above each cylinder. That space adds to the combustion chamber and lowers the compression ratio; only gaskets of the same bore are comparable. Here, the two gaskets have close bores, 75.5 mm and 75 mm.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts | F250 | not published by the manufacturer |
Before fitting, run a straight edge over the head and the block to check their flatness, and have either one resurfaced if necessary. Cometic checks the flatness of each of its CFM-20 gaskets. This check holds for the Colombo V12 as for any other engine.
| CFM-20 Cometic A galvanized steel core, lined on each face with a soft asbestos-free compound blending aramid fibres, mineral fillers and elastomer binders. This layered structure, between metal and fibre, joins the stiffness of steel to the give of the compound. It is offered here as two part numbers: 75.5 mm with a 1.09 mm thickness, 75 mm with 1.50 mm. |
Gasket bore. The Cometic CFM-20 gasket is offered in 75.5 mm (C14101-043) and in 75 mm (C14109-059).
Thickness. For the original gasket of the Colombo V12, the manufacturer gives no thickness. 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: measure the removed gasket and compare its size with the two part numbers offered, 1.09 mm and 1.50 mm |
| Skimmed cylinder head, make up the lost height | Two thicknesses exist, 1.09 mm and 1.50 mm: take the one nearest to that of the removed gasket, plus the material taken off in resurfacing |
| Forced induction build, lower the ratio | 1.09 mm, if the thickness measured on the original gasket at removal is lower |
| Naturally aspirated build, raise the ratio | 1.50 mm, if the thickness measured on the original gasket at removal is higher |
With no published original thickness, use a dial gauge to measure how far the pistons stand proud of the block's gasket face, above all if the removed gasket is thinner than 1.09 mm: this reading gives the clearance left between piston and head.
 | Cometic Gasket, Inc. is an American manufacturer of gaskets and sealing solutions for engines, founded in 1989 in Concord, Ohio. Its reputation rests on the made-to-measure gasket, cut to the bore and thickness requested; all production takes place in the United States, from American raw materials. The part numbers C14101-043 and C14109-059 are its own. |
| Criterion | Original gasket, part number not published | Reinforced gaskets |
| Construction | Construction not stated by the manufacturer | Galvanized steel core and asbestos-free compound (CFM-20) |
| Gasket bore | not published by the manufacturer | 75,5 / 75 mm |
| Thicknesses available | thickness not published by the manufacturer | 1.09 to 1.50 mm |
| Compression ratio adjustment | None | Through the thickness chosen |
| Resistance to overpressure | Limited to standard output | Designed for forced induction |
| Model | Engine code | Power | Years |
| Ferrari 250 Europa | F250 | not published | 1954-1955 |
| Ferrari 250 GT | F250 | not published | 1954-1959 |
| Ferrari 250 LM | F250 | not published | 1963 |
OEM part number: not published by the manufacturer.
Important: the part numbers on this page suit the manufacturer's Ferrari 250 Europa, 250 GT and 250 LM: the cylinder bank is not specified, and a V12 has two, so check before ordering, along with your engine's bore, 75.5 mm for C14101-043 and 75 mm for C14109-059.
When the original gasket reaches its limits, this CFM-20 gasket takes over: the steel core keeps its shape under combustion pressure, while the soft compound on both faces follows the small flaws of the head and block. The Colombo V12 finds here two gaskets, one at 75.5 mm, the other at 75 mm.
On an engine driven to its limit, the head gasket is the first part to fail, the weak point of the top end. A reinforced gasket prevents the leak, whereas the head removal that follows, a long and delicate job, costs much more than the gasket. This holds for the Colombo V12 as for any hard-driven engine.
