an AC Engine?
Blocks, Studs & Water
Spare Parts List One - Attaching Parts, Seals
Parts List Two - Crankshaft & Cross-shaft
Assemblies and Chains
Spare Parts List Three -
Pistons & Liners
Spare Parts List Four - Sump Assembly
Spare Parts List Five - Cylinder Head
Spare Parts List Six -
Spare Parts List Seven -
Engines for Sale and Used Parts
Parts List Five - Cylinder Head Assembly......
New Rockers at
bottom of page *
A complete and newly restored
and assembled Vintage cylinder head assembly,
incorporating new guides, valves, springs,
rocker shaft, collets, caps, mousetrap
springs, pedestal studs and reprofiled
most from a brilliant design
cylinder head assembly is a vital part of any
engine, especially with the AC as the overhead
camshaft design means that all the valves,
rockers and the driven timing gear are carried
in the head. This not only makes for an
efficient engine but also simplifies maintenance
as access is so easy. There are quite a
few moving parts however, - although rather less
than in some overhead cam layouts - and they do
wear. Replacing worn parts and taking care
in their assembly can pay dividends in engine
performance and reliability. And we can
supply the parts you will need.
types of head
generations of AC cylinder head have less
difference between them than the cylinder blocks
have and are, to a large degree,
interchangeable. The distinguishing
Water pump mounted on the front of the head
on three studs at rectangular water passage
in head and driven by the camshaft.
Longitudinal recesses on lower face.
Narrow rollers; inverted tooth timing wheel.
Early with cam driven water pump as above;
later by belt with pump mounted on four
unequally spaced studs. Narrow
rollers, inverted tooth timing wheel later
changed to Duplex type.
early UMB: Thermostat
housing mounted on front of head on two
studs at circular water passage.
Narrow rollers. Water pump now mounted
on side of block and not on head.
late UMB/UMC: As
above. Wide rollers.
As above but lacking the narrow hot-spot
water passage between and beneath the centre
pair of Carburettor studs. Equal
length head studs.
are the most often replaced items in the
cylinder head and we keep good stocks on the
valves are made from best quality materials and
are Stellite coated for use with hardened
seats. Please note that at engine or
cylinder head overhaul it is advisable to fit
hardened seat inserts for use with new valves.
valves with semi-tulip heads, large diameter
heads, waisted stems etc are all available to
Many of the camshafts that
we see in AC engines are in very poor condition,
whether rust pitted, worn on the cam lobes or
bearing journals or even bent! While it is
sometimes possible to find a replacement used
shaft in good condition, the supply is finite.
Our new and reprofiled camshafts fill the
growing gap in supply and provide enhanced
Fast Road Camshaft
Designed to our
specification by a leading expert in the field,
our fast road camshaft not only provides much
better performance but actually makes the engine
feel smoother and allows it to go on revving
when it would normally run out of breath.
This camshaft has been raced on the Continent
where one owner said, 'It made the difference
between night and day!'
For those seeking even
higher performance we can also supply a sports
camshaft. Early ordering for these items is
Camshafts for racing may
be supplied to bespoke profiles according to
alternative to a new camshaft is an exchange,
re-profiled one. Reprofiling is a good way
of recycling well-used camshafts for further
active life and, at the same time, providing
some extra performance. We keep several in
stock to various configurations or, if you
prefer, we can re-profile yours to your own
requirement (within its wear characteristics).
Journals and Bearings
When significant wear has
taken place in either or both the camshaft
journals and the bearings in the cylinder head
the situation can often be retrieved by
machining both bearings and camshaft and fitting
shell bearings., as illustrated below.
guides can suffer from serious wear and
replacing them is an essential part of any
overhaul. Our guides are precision
machined from cast iron and the bores finely
honed for smooth valve operation.
Valve springs inevitably
become tired after long use and can no longer
perform their task of closing the valve quickly
and of maintaining the required seal between
valve and head. We always keep plenty of
inner and outer spring pairs in stock.
For use with uprated,
higher performance camshafts we also stock
springs with higher closing pressures and fewer
coils to prevent coil binding that could occur
with cam profiles providing increased valve
Sometimes it is necessary
to adjust the fitted height of valve springs to
ensure consistent valve closing pressures on all
valves. We are currently developing a
range of different thickness spacer shims for
this purpose. At the moment we have 0.020"
shims in stock; these may be used in
multiples to achieve consistent spring height.
Valve Gear Fittings
Valve spring caps, valve
stem caps, adjusters and locknuts and valve
collets all wear but we have good stocks of new
Uprated Rocker Shaft
A weakness of the original
rocker shaft is that it only extends a short way
into the bearing pedestal at the front of the
cylinder head. With time and use the
restricted bearing area can allow the front of
the rocker shaft to fret up down, causing the
bearing to wear oval making correct valve
adjusting impossible (see above).
Our uprated rocker shaft
overcomes this problem as it has been extended
at the front end so that it seats more deeply in
the front pedestal, thus being more firmly held
in place. Additionally, the shaft is
extended at the rear to take advantage of the
considerable amount of unused, extra bearing
space available in the rear pedestal.
These shafts have
been proven in usage on the race track.
Please note that we no
longer supply rocker shafts to the original,
shorter AC design owing to lack of demand.
brass exhaust manifold nuts can smarten an
engine bay enormously. They can be used on
either the cast types of manifold or the tubular
Ace/Aceca type where access can be restricted.
valve adjustment can often become difficult
owing to rocker rollers and pins being very
worn. Our new rollers and pins cure the
problem. We stock the later, wider roller
as well as the earlier, narrower type. In
either case the pin should be ground to suit the
somewhat variable width of the rocker and peened
The spacing of rockers on
their shaft, even on very original engines, can
be somewhat haphazard. With our shims,
much more accurate spacing and alignment
of the rockers with the valve stem and the oil
supply hole in the rocker shaft can be achieved.
Often ignored, the rocker
spring serves a useful purpose in keeping the
rocker roller in contact with the
camshaft. When the spring weakens the
rocker is allowed to 'chatter' against the
cam. This accelerates wear to the
Camshaft Location Bearing
This particular bearing
is another much ignored item whose presence and
function is just taken fro granted. They
do wear however and this allows the camshafts to
move back and forth. They also provide the
oil passage to the camshaft and rocker gear and
if worn, cause oil pressure to drop.
Pedestal Studs and Nuts
pedestal studs often have very poor threads at
the top and it can be difficult to tighten the
rocker cover nuts, particularly if the nuts have
been over-tightened in an attempt to prevent oil
leaks and the stud thread strained and those in
the nuts stripped. Our high-tensile studs
are made a quarter of an inch longer at the top
so that the thread engages much more deeply with
the nut, thus allowing more effective tightening
down and reducing the risk of oil leaks,
especially with fibre washers fitted beneath our
new, very high quality stainless steel domed
and tried in competition, our adjustable timing
sprockets not only provide a full set of new,
unworn teeth but allow much easier assembly and,
once installed, very fine adjustment of the
valve timing without the tiresome and perhaps
risky business of splitting the
Initial setting up becomes much easier than with
a standard sprocket and if you are involved in
motor sport, finding the optimum valve timing
for different events is made very simple.
We see a lot of rocker
boxes that are cracked or otherwise damaged, the
most common cause being over tightening to
prevent oil leaks without renewing the rocker
box gasket. With the PVT and post-war
engines a replacement rocker box can sometimes
be found but with the numerically sparse vintage
models this is seldom the case. Our
recently introduced vintage rocker box removes
this problem completely.
For some reason there are
plenty of bare heads around, their fittings
having been purloined for use elsewhere.
Quite often such plundered heads have a
perfectly repairable fault, perhaps a crack or
corrosion but lacking sufficient parts, just
gather dust. Our new pedestal
castings now make it possible to bring abandoned
heads back into use. The castings are part
machined and pilot bored ready for final
matching to the head in question.
Note: We hold a
substantial stock of cylinder heads and have
begun a programme of restoration to bring them
back into use and to help alleviate the known
shortage of sound heads for the AC engine.
Further details will be announced in due course.
Our new valve
rockers are proving increasingly
popular. Each rocker is a precision
machined investment casting that duplicates
the geometry of the AC rocker original but
which offers approximately twice the
strength of the original. The cam
follower is a roller bearing that is
slightly larger in diameter than the
original to lessen wear on the cam lobe and
which also offers a small increase in valve
lift. These rockers are used to
best advantage with high lift camshafts,
where their increased strength resists the
breakages sometimes seen with the