Classic Ford – September 2019

PERFORMANCEHEADGASKETS

Therearequitea fewdifferenttypesof

performanceheadgasketavailable.Inthe

FordtuningworldGroupA upratedhead

gasketsareoftenseenasthefirstavailable

upgrade.Thesearebasedheavilyon

thestandarddesign,butaremadefroma

moredurableandmoreresistant

compositematerial.Theycantherefore

copewiththeincreasedstrainsofa higher

performanceenginethanthestandard

gasket,butarealsoa directswapand

operateinexactlythesameway.

Anothermethodofupratingthehead

gasket,whichwasparticularlycommonin

themid-80s,is tofit a setofCoopersrings

(above).Thesereplacethefireringsona

traditionalheadgasketwitha much

heavier-dutysetofO-rings.Theblockneeds

to have a lip machined around the top of

each cylinder to allow the Coopers rings to

be fi tted, and as the head is torqued down

the rings will crush and deform to create a

seal between the cylinder head and block.

The resulting seal is much stronger than

with a traditional head gasket, enabling far

greater cylinder pressures to be reached

without the head gasket failing. This type of

system was commonly used on race

engines, and in particular high-boosting

turbo engines. To accompany the Coopers

rings a Group A-style head gasket without

any fi re rings can be used to seal the oil and

water ways. Alternatively some top-end

motorsport engines didn’t use a head

gasketaswe’dknowit atall.Insteadthey

usedCoopersringstosealagainst

combustion,andtheblockwasalso

machinedtoacceptrubberO-ringsaround

theoilandwatergalleries,thereforenot

needinga single-pieceheadgasket.

However,Coopersringsarenowseenas

oldtechnology,andmanyenginebuilders,

includingtheguysatBurtonPower,agree

thatformostenginesa goodmulti-layer

steel(MLS)headgasketwillofferthesame

levelofperformanceasCoopersrings,but

withouthavingtomachinetheblock.

A MLSgasket(above)is madeupof

multiplesteellayersjoinedtogetherto

forma gasket.BurtonPowerstocksa

complete range of Cometic MLS gaskets,

so we were able to pull one apart to see

exactly how they work.

The outer two layers of an MLS head

gasket are embossed and on Cometic

gaskets are covered in a fl ouroelastomer

rubber-based material called Viton. These

outer layers are what give the gasket its

sealing properties. When the gasket is

installed the embossed edges deform

slightly to create a seal. The gasket’s

strength comes from the centre layer, which

is made from untreated stainless steel. The

centre layer is also what gives the gasket its

thickness, as this centre shim is available in

a range of different sizes. Four layer gaskets

featuretwocentreshimsaswellasthetwo

outerlayers,withtheextracentrelayer

offeringevengreaterclampingpressure.

AccordingtoBurtonPower,Cometic

gasketsareavailableoff-the-shelfinsizes

rangingfrom1 mmto2.5mmthick,

andcanevenbecustommadetoany

thicknessrequired.Thickergasketsarenot

necessarilystronger,butdoofferthe

enginebuilderthechancetotweakthe

compressionratioeasilyaftertheheadhas

beenskimmed,orif a slightlylowercomp

ratiois required.

OnedownsidetoMLSgasketsis that

becausetheydonotcrushandtherefore

moveaboutinthesamefashionasa

compositegasket,theyarebestusedwhen

thetwomatingsurfaceshavebeen

machinedtotallyflat.Fittinga steelgasket

toa slightlyunevenblockorheadsurface

couldresultinfailure,whereasa composite

gaskethasmore‘give’init to

accommodatetheseirregularities.

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The head gasket is probably the most stressed

gasket in the whole engine as it has to seal oil

ways, water ways, fuel/air mixture and exhaust

gases, and has to operate under the extreme

temperatures and pressures of mating the

cylinder head to the block. This is why the head

gasket is amongst the most common gaskets

to fail in a high-performance engine.

Older head gaskets like those used in the

original Lotus twin-cam engine were actually

made from copper and asbestos, but

modern-day standard gaskets are made from

a composite material (which incidentally is

often incorrectly referred to as a fi bre gasket).

The composite material is coated in a wax-like

fi nish, and the head gasket will usually feature

a bead of silicone around the oil and water

ways to help create a better seal.

The way a head gasket seals the oil and

water ways is pretty conventional, but the

most diffi cult job a head gasket has to do is

create a seal between the cylinder head and

block around the combustion chamber. The

immense pressures and heat which are

generated here make it an intrinsically diffi cult

joint to seal.

To overcome this, a head gasket features

steel rings known as ‘fi re rings’ that seal

around the top of the cylinder. The fi re rings are

crushed when the head is tightened onto the

block (which is why torque settings are critical

to ensure optimum gasket thickness is

achieved) and creates a seal capable of dealing

with the pressures and temperatures involved.

However, when you start tuning your engine

these pressures and temperatures are

dramatically increased and frequently lead to

failure of the standard head gasket. Therefore

performance upgrades are needed.

Standard head gaskets

Multi-layer steel head

gaskets are available

in different