HMC is the
car company most people have never heard of. Back in the late 90s a group of
car enthusiasts in Stroud came up with the cracking idea of bringing the 1960s
Austin Healey a new lease of life.
This was
in an era when retro cars and styling were in vogue and their plans were to
create a 'continuation car' - one that borrowed a lot of the style and
character of the original, but updated for a modern audience.
The result
was the HMC MkIV, a brilliant factory-built sports car that is eons away from
the kit car copies that try to breathe new life into the Austin Healey style.
Developed with input from the Healey family, less than 200 were built before
parts dried up. It would even have been called a Healey if a last-minute
trademark dispute didn't scupper those plans.
What makes
the HMC so good is its spaceframe chassis - just like a TVR - and its thumping
3.9 litre Land Rover V8 engine. This was one of the last developments of the
original 1960s Rover V8, a power plant that was dropped into many, many
brilliant cars from the Rover P5B and SD1 to various TVRs and MGs. Light,
compact and torquey, this V8 is also durable and reliable.
Things
that go bang
Until, at
least for this car, one day late last year. In fairness to the engine, it
wasn't it's fault that an oil pressure switch let go, probably a symptom of age
or cheap replacement parts somewhere down the line. The car is run by our
sister company Great Escape Cars and was out with a customer - although they
stopped quickly the car lost oil faster and cooked the heads.
We took on
the job of identifying the problem and proposing a solution. it quicky became
clear that a rebuild would be a risky proposition - it wasn't clear whether the
engine had gone porous. Rebuilding it wouldn't necessarily create a reliable
engine.
We
recommended sourcing a good second hand unit. Removing and replacing the HMC
engine is not easy but for us it is a known quantity - we've taken this one out
several times over the years to check it over and replace various parts.
4
goes into 3.9
The car's
owner, who leases the HMC to Great Escape Cars, found a good, rebuilt 4 litre
Rover V8 and arranged delivery to us. Unfortunately - and probably surprisingly
to many - there is a huge difference between the 3.9 Land Rover engine and the
4 litre. This gave us some problems when it came to stripping the old engine,
building up the new one and fitting it to the car.
The 4
litre Land Rover 'Gems' engine differs from the 3.9 in some fundamental ways.
Unlike the smaller engine it doesn't run off a distributor fed by the
camshafts. Instead it has eight individual coil packs to create the spark for
each cylinder. The crankshaft main bearing caps are crossed bolted for extra
strengh and the crankshaft has larger journals, making it larger overall.
If this
wasn't enough the inlet and outlet manifolds are also different, as is the
injection system, timing cover and sump.
Overcome
differences
These
differences meant that we could only use the cylinder block, crankshaft,
pistons and cylinder heads from the 4 litre Gems engine.
To
overcome the problems we installed a new camshaft with distributor drive and
hydraulic followers as well as a new timing chain. These changes enabled us to
fit our original front timing cover, distributor and water pump. To avoid the
risks associated with using potentially worn parts, we sourced new rather than
use the existing parts from the old 3.9 litre engine.
To build
the 4 litre engine up we fitted our original sump and inlet manifold with
injection system and installed the old exhaust manifolds. These needed slight
modification because the holes did not align with the new engine.
We then
converted the rear of the crankshaft to accept the manual transmission flywheel
and clutch assembly for the HMC, which we also replaced. This required a spacer
for the front of the crankshaft to accommodate the front pulley because the
Gems engine has a slightly longer nosed crankshaft. New gaskets, oils and
filters were used throughout.
The
Result
The work
to convert the 4 litre engine to suit the HMC demonstrates the value of
experience with a particular car. The HMC is a very low volume sports car, and
each one has its own quirks, but we have maintained this particular car for 7
years. So we were able to shortcut some of the head-scratching and confusion
that might have confronted other workshops when faced with this problem.
Once
fitted the car developed a radiator leak, which was repaired locally by one of
our specialists. And initially the car was overheating. This was a simple fix
requiring a new thermostat.
The new
engine is running well and gives the HMC a little extra performance over the
3.9 litre V8. Although using the 4 litre created some additional problems, our
knowledge of this car and engine meant we could plough through and give the
owner a cost-effective solution and, above all, give Great Escape Cars a
reliable hire car for the new season.
Classic
Fixers maintains the Great Escape Cars' classic hire fleet, which is the
largest in the UK. You can find out more about them at www.greatescapecars.co.uk
or call 01527 893733.
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