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:Tech Tips:
Gasket Installation Tips
With today's modern engines, it is extremely important that gaskets are fitted correctly.
The following
information will help to ensure a quality and lasting result.
GENERAL
The two most important factors in successful gasket installation are that both surfaces
are clean and flat. Gasket failure will most probably occur if this is not the case. It is
extremely rare to have a faulty gasket, especially a cylinder head gasket, so if there is
a gasket failure, look for the cause before fitting a new one.
A distorted head or block, overheating caused by a partially blocked radiator or block
containing sludge, a faulty thermostat, incorrect ignition timing, are some of the common
causes.
Always use a quality coolant in the cooling system (not just water) to reduce internal
corrosion. Some vehicle manufacturers insist on a particular brand and grade of coolant
for certain models.
CYLINDER HEADS
The head and block must be undamaged and flat to within 0.05mm (0.002") along and
across the sealing surfaces. The head and/or block MUST be re-surfaced if distortion
exceeds this measurement. This is even more critical with aluminium heads and blocks. The
recommended surface finish is between 1 and 2.5 micrometres (40 - 100 microinches) Ra.
Check the thickness of the head after machining to ensure the head bolts are not too long
so that the threads bottom out before the head is tight. If this is the case, use a shim
with the head gasket or add an extra washer under the head of the bolt. Do not machine
heads more than manufacturers specifications as excessive machining may cause
gasket/engine failure.
Alloy heads must be checked for hardness as constant heating and cooling causes the
material to soften, particularly if the engine has overheated. Heads with a Brinnell
hardness of less than 75 should be discarded The result of using a soft head is a leaking
head gasket as it is impossible to keep the head bolts at the correct tension as they sink
into the top of the head.
Where surfaces with threaded holes have been machined, the holes must be chamfered to
prevent the
being drawn up above the surface when the bolts are tightened. All bolts and studs must be
undamaged and assembled with a light film of oil under the bolt heads and washers and on
the threads of the bolts. If the bolts penetrate the water jacket, use a non hardening
sealant. Oil on the bolt heads and threads can increase the clamping load on the cylinder
head by 2 - 3 times. If torque to yield bolts are specified,
they MUST be replaced. If you do not know if your engine has torwue to yield head bolts
fitted ask our staff.
No sealants should be used when assembling non coated and beaded head gaskets. Non
retorque head gaskets such as Gasmiser Superseal are made from pre-tensioned material with
a special coating and a silicone bead to assist in the sealing process. Standard
non-coated head gaskets may be coated before assembly with a suitable sealant if required.
A silicone bead alone does not signify a non retorque head gasket. Most engine
reconditioners recommend that ALL head gaskets, even the non retorque type, be retensioned
after 500 - 800 km to ensure a good and lasting seal. This is especially important on
later model high compression engines where the correct tensions are critical. Retighten
cast iron heads at operating temperature and aluminium heads when the engine is cold.
Cylinder heads must be tightened in the correct sequence in stages in accordance with the
manufacturers specifications with a good quality tension wrench. In the absence of this
information, tighten in 3 stages, working outwards from the centre in a radial pattern.
MANIFOLDS
Some manifolds, including inlet manifolds, are prone to distortion and may have to be
resurfaced before fitting new gaskets. Always retighten after 500 km.
OIL SEALS
Oil seals and valve stem seals should be assembled with a light film of oil. Oil seals
should be fitted with a proper tool otherwise distortion and/or damage to the sealing lip
can take place resulting in a leak. Never fit a seal to a shaft that has been marked by
the old seal otherwise a leak will re-occur. Have the shaft machined first.
MISCELLANEOUS
Paper and cork gaskets may be coated with a sealant before installation to create a better
seal. All
components of pressed metal e.g. some valve covers must be checked for distortion,
especially around the bolt holes, and be flattened where necessary as unequal pressure on
the gasket will result in oil leakage and gasket damage. This particularly applies to cork
gaskets which should not be over tightened.
This information was supplied by Gasmiser Gaskets,
suppliers of Gasmiser Superseal.
