What is an AC Engine?
Blocks, Studs & Water Jackets
Spare Parts List One - Attaching Parts, Seals & Gaskets
Spare Parts List Two -
Crankshaft & Cross-shaft Assemblies
Spare Parts List Three - Pistons & Liners
Spare Parts List Four - Sump Assembly
Spare Parts List
Five - Cylinder Head Assembly
Spare Parts List Six - Ignition,
Spare Parts List Seven - Water Pumps
Engines for Sale and
Parts List Three - Pistons & Liners......
particular aspect of the original liner design that can lead to trouble is
that a thick figure-of-eight gasket is needed beneath the liner in order
to set the required protrusion of the liner above the block in order to
ensure that the head gasket will seal properly. The gaskets were
either thick and squashy copper and asbestos or aluminium sandwiched in
paper (or Hallite). The former had the advantage of being easy
to fit and with a more or less guaranteed seal-by-compression but the
disadvantage that over time the gasket would lose its compliance and the
liner would sink, thus breaking the seal of the head gasket, the latter
often being blamed for failures arising, such as water in the
advantage of the ali and paper sandwich gasket is that the liner height
can be set more accurately but the disadvantage of being very
time-consuming and fiddly to fit, a further drawback being that sealant is
required between each mating face and sealant has thickness that changes
when the head is tightened down. Both types of gasket require
renewal virtually whenever the head is removed in order to regain the
correct liner protrusion and this would mean stripping the engine, even if
the cause were only a blown head gasket! Very often this was/is not
done, a new head head gasket installed which would almost certainly fail
designed our cylinder liners to overcome this weakness as they are longer
in the body than the original liners and require only a thin gasket and
minimal sealant between the liner and the liner bed in the block and once
installed, the protrusion is automatically set (assuming that the block
still conforms to its design dimensions and that its mating surfaces have
not been skimmed).
with a new water jacket fitted and new liners installed.
block new water jacket and installed new liners being checked for
uniformity of protrusion.
new liners, showing different body length
higher compression ratio pistons
Our traditional pistons
closely resemble the flat-domed type originally supplied in AC engines but with
the exception that they are designed with narrower ring grooves to accept
more easily available modern rings made in Germany by Goetze. The
gudgeon pins are made in the West Country by a highly reputed supplier
of precision made components. The pistons are only available
in standard bore size (65mm) and are usually supplied with our new
The pistons have been used successfully in the Mille Miglia on at least
three occasions. We have also sold many sets to customers for less
The claimed compression ratio (CR) for the domed pistons has always been
9.0:1 and they are commonly referred to as such. In fact, the CR
was actually around 7.5:1, which provides
perfectly acceptable power output for most uses.
In addition to our
traditional pistons, we can supply bespoke forged pistons made in the
USA to special order,
with CR and bore size to suit. These can be made to suit a a wide
range of preferences e.g. shape of dome, with valve recesses, normal or
slipper shape for lightness, various ring groove dimensions.
As these pistons are
made to our requirements they come with the same, easily obtainable
rings as the traditional pistons.
Delivery times vary but
a few weeks should be allowed when ordering. We sometimes have a few
sets on the shelf so it is always worth enquiring just in case we have the
ones that you need in stock already.