How does this thing work then?
AIUI, it's basically a two-cylinder opposed-piston cylinder-ported
petrol two-stroke, with a third cylinder used separately for
compression. There are two crankshafts, geared in the Jumo 205 style.
The question is, what's in that middle cylinder? If it has a piston
rod and gland, that suggests it's double acting? if it's double
acting, then surely that's a single piston, not opposed pistons? So
is this a 5 piston engine, with two working cylinders? Or three holes
and six pistons?
Kim's pics, for convenient linking:
Talking of separate pumping cylinders, has anyone heard of Lamplough
from around 1905?
According to Phil Irving in "Two-Stroke Power Units" (and he ought to
know!) it has two power cylinders with a pumping cylinder between. The
pumping pistons are double acting with the space between them feeding
No. 1 power cylinder and the two spaces behind them feeding No.2.
The unlikely looking Lamplough illustrated works on the 'twingle' or
folded uniflow principle with each pair of parallel cylinders sharing a
common combustion chamber. Later examples include DKW, Puch and EMC.
Here's what I know about them. ............
The Vincent Marine Engine
J. Kim Siddorn
A classic example of being conceived in good time but born too late, the
Vincent Marine Engine was originally made for an air/sea rescue role and
fitted to airborne lifeboats, a complete aluminium shell which could be
dropped to men in the water from an aircraft.
Vincents gave up motorcycle production during the war, concentrating on
making specialist components at their Stevenage factory, one of which - for
instance - was rocket fuses. Phil Vincent's agile mind was never far from a
novel solution to a perceived problem and he found an Air Ministry brief for
an engine in which frugality of fuel consumption was vital - and the other
parameters were tough, too. It had to be capable of being started by hand,
fully radio screened, waterproof (sic!), light in weight and smooth running
and able to run for long periods with little maintenance. The construction
had to be compact so that the hull of the lifeboat would fit cleanly against
the fuselage of the aircraft that carried it and be able to withstand a 5G
deceleration as it hit the water. The specification called for 15 b.h.p. at
3,000 r.p.m. from an engine that had to be able to run satisfactorily on any
petrol, from 70 octane "pool" to highly leaded 120 octane aviation spirit.
Worked up from an original concept by Phil Irving in 1942, the 500cc
Lifeboat Engine (as it became known) was produced with Pacific rescue
missions in mind. For a fuel consumption of 50 gallons, the boat seemed to
be capable of a total mileage of over 1,000 sea miles at an average speed of
5 knots compared to an Austin marine engine's best performance of 500 miles
at 4 knots on the same quantity of petrol and the prototype passed its AID
inspection out of the box.. However, over 800 hours of development,
designing a reverse gear, electric starter etc and a vacillating Air
Ministry kept Vincents busy until 1949 and that was too late, only fifty
being made. Of this single batch, there are around a dozen left, this
example having the s/n 44.
For the technically minded, the device weighs just 256 lbs (116 kilos) and
has a watercooled inlet manifold and exhaust. It is a two-stroke cycle, twin
crankshaft opposed six, the pistons moving inwards to form a common
combustion space, thus, this six has three bores. The centre bore of the
three provides compressed mixture for the outer two cylinders, the mixture
not being compressed in the crankcase as in normal two strokes. The pumping
cylinders have cross heads like a steam engine, allowing straight, round
section connecting rods to be sealed from the crankcase with gland seals.
The mixture is circulated both "above" and "below" the pumping pistons,
transferring to one set of power pistons on the inward stroke and to the
other set on the outward stroke, thus making best use of the capacity
available. The inlet charge must be well and truly mixed by the time it gets
squashed and ignited!
A great advantage of this layout is that the port timings of the pistons on
one crankshaft can be varied in relation to those on the other crankshaft.
One pair of pistons control the transfer ports and the other the inlet
ports, so the port timing can be readily varied to give the best results. As
the gas moves in only one direction, it is called a Uniflow engine. In a
conventional two-stroke, the same piston has to control both transfer and
exhaust. This system may be simple, but port timings will always be a poor
compromise compared to that on a two crank system and very wasteful of fuel,
especially at full load or idle, ask any Petter M type owner! The
development of the Lifeboat Engine progressed to a stage where the fuel
consumption became extremely good even by four-stroke standards.
Looking nothing like an engine, the lumpy rectangular thing might be
anything at all. Only the two spark plugs sticking up out of the block and
the brass-bodied Amal carb give it away.
Wearing its original coat of Admiralty grey paint, the author's unit in
these pictures is in pretty good condition, somewhat chipped and worn as one
might expect in something which has been around for over fifty years. The
only things that are missing are the ancillaries cover that covers the
starter, generator and magneto and the recoil starter that mounts at one end
and contains a huge clock spring. No-one has these items out there, I
At the time of writing in August 2002, the engine has only been run briefly
in order to check it out, prior to being fitted with tanks and a cooling
The marine engine was doubled up into a flat six twelve piston engine
intended to drive a 10Kva generator after the war. It was unsuccessful due
to the impossibility of maintaining square faces during the machining of the
huge and complex crankcase casting. It went through very considerable
development, but it was just too complicated for its own good. There was a
description of this in issue No: 156 of Stationary Engine Magazine for
Irving again:- "the difference in displacement caused by the presence of
the half-inch diameter piston rods was disregarded."
BTW Kim, Irving also states that he spent "over two years' intensive
work" on the engine based on Vincent's patents, rather than the other