From: hotrod@dixie.com (The Hotrod List)
Subject: Engines of Yore #2
Date: Sat, 09 Jan 93 05:13:48 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.
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Posted-Date: Saturday, Jan 09 00:13:28
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                         Engines of Yore:  Part 2.
                Ariel Square-4.      created 26 April 1992
             by Dave Williams   dave.williams@chaos.lrk.ar.us

 Much of the Ariel's mystique may have come from its relatively enormous
997cc displacement.  In many ways, the Square-4 was two 500cc twins
mounted one behind the other, with all the usual weirdities of preWWII
British engineering.  We'll be discussing the second generation "light
alloy" Square-4.

 The crankcase followed normal practice, being vertically split aluminum
halves.  Unlike many of its contemporaries, the Ariel provided a wide
flange at each half to minimize oil leakage.  The crankshafts are
assembled from a Z-shaped cranked section, a circular flywheel bolted
to a central flange, and two bolt-on counterweights.  The British were
really into flywheels.  The front and rear cranks were different, the
rear having extended end shafts for clutch and magneto drives.  The
single camshaft sat in the middle of the crankcase and above the
crankshafts.  It was held by a plain bearing on the right (driven) end
and a plain bearing on the left.

 The engine used pressure lubrication.  The left side of the cranks ran
in ball bearings, the right side and rods in plain bearings.  There were
no center bearings, which was normal practice for the time.  Oiling was
via low volume plunger pump.  A gauze filter about the size of a 35mm
film can was provided for cleanliness.

 The crankshafts were arranged 180 degrees out of phase to minimize
vibration (which worked quite well, incidentally) and were phased by
large gears on the left side.  The engineers evidently didn't quite
trust plain bearings, as this was the side they put the ball bearings
in.  Modern designers would have cut teeth in the flywheels since they
nearly touched anyway, or used a full-circle flange on one of the rod
throws and toothed that.  The phasing gears were covered by another side
plate, the rear of which mounted yet another ball bearing to stiffen the
crank before the primary drive sprocket went on.

 Connecting rods were aluminum with replaceable bearing shells.  The
rod bolts were quite modern looking with reduced shank diameters and
precision-ground outside diameters to locate the big end caps.  The
British have never quite trusted screw threads, however.  These fine
bolts were finished off with castellated nuts and cotter pins.  Pistons
were conventional aluminum, dish top, 5.8:1 CR.

 The Ariel's cylinders were all cast as one 4-cylinder block also
providing the pushrod tubes.  This was much different from usual
practice, which provided individual cylinders on twins.  The cylinder
block was cast iron, as was the main head casting, which provided the
four combustion chambers, fins, and the bottom half of the intake
manifold.  The aluminum rocker box set atop this, with a final aluminum
rocker cover.

 The overall design of the cylinder block and top end is difficult to
justify by any rational means.  It was surely expensive to build, and
it is difficult to imagine a worse way of arranging a square four.

 The main head casting was held down by only three bolts around each
cylinder.  The combustion chambers had no quench area.  The intake air
came straight down from above with an X shaped runner set cast right
into the head, which surely warmed the inlet air more than necessary.
The Ariel's engineers made the intake and exhaust valves the same size
and mounted them straight up in the center of the chamber.  The eight
pushrods came up from between the cylinders, through the bottom head
casting, and up into the light alloy rocker box.  The rocker box also
contained part of the intake tract, turning an abrupt 90 degrees and
leading back to a single carburetor flange.  Incoming air had to turn
three 90 degree bends before it could get to a valve.

 The valve gear is fairly ordinary shaft mounted rockers, except the
Ariel designers designed the rockers for a 1:1 lift ratio.  Pushrods
were aluminum.  The intake and exhaust lobes are identical, with lift
at the valve was only 5/16".  The cam timing was quite modest.  Dual
concentric valve springs were used with a 90 pound seat pressure,
which is about the same pressure a 350 Chevy uses to control its much
heavier valvetrain.  I can't imagine why such stiff springs were used
with such a mild cam profile, and I'd bet money the long, slender
camshaft (unsupported in the middle, remember) would have flexed quite
a lot.

 Since the Square-4 couldn't suck any great amount of air in, its
designers didn't worry unduly about getting air out.  Grotty iron
exhaust manifolds bolted to each side, and both cylinders shared a
common exhaust pipe.

 The Ariel Square Four produced 38 horsepower at 5,500 RPM from 997cc,
not exactly sizzling even by the standards of its day.  The square
layout probably never caught on due to carburetion problems; the only
other square fours I'm aware of are two strokes, which found the square
layout to be an efficient means of using space.  Yamaha and Honda have
found the V-four to be easier to carburet and free of the hassles of
double crankshafts and their phasing gears.

-30-
                           

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Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
Newsgroups: alt.hotrod,wiz.hotrod