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Simplex Marine Motor

Pompei’s Marine Agent for Simplex Marine Motors and Parts. Jack Pompei only used simplex marine engines in his rescue boats with some 2000 lives saved, and many more sunken boats pulled in form the depths with his trusty simplex twin marine motors. And after some 50years of service still going strong today. Contact  “I work on alot of old marine motors and it gets harder and harder to get good parts for them. With the Simplex, parts are stilled made here in Australia since 1930 for the motors. No having to replace a good motor in the future.” I’m looking at doing a swap service on the carby and we will have some more new magneto’s in stock in 2011. As well as a full range of ORIGINAL Magneto parts in stock. read here for info on the simplex. For simplex starter motor / alternator contact us $1000.00, make life easy.

Simplex four-stroke petrol inboards that, in essence, were unchanged since the 1930s. They have a beautiful classic note. Fitting a Simplex in older timber launches and cruising yachts (such as an H28) is far more in keeping with the boats’ original designs than a diesel. And although Simplex engines are from another era, one far less complex, they are pure marine engines that still have a standard of engineering not found in many small diesels that are marinised from industrial units.


An example of this engineering is the flywheels located forward of the engine blocks, enabling the engines to be mounted deep in the bilges of full-keel yachts. The flywheel location also biases engine weight further forward in launches where traditionally passengers sit aft of the engine, which can seriously affect hull trim in relatively fine-sterned displacement hulls.

Every Simplex engine is hand-built by a qualified fitter and turner and has a delivery time of about six weeks. Apart from the alloy piston(s), the entire engine is cast iron with all reciprocating components such as the crankshaft dynamically balanced to reduce vibration. All engines have replaceable hardened valve seats enabling them to run on standard 91 RON unleaded petrol.

Because the side valve location requires only short pushrods from the gear-driven camshaft, there’s no need for pressure lubrication, eliminating the possibility of an oil pump failure. And as the maximum engine revs are only 1200, reduction gearboxes are not required. The standard 1:1 ratio ahead/astern boxes have cast iron cone clutches with the boxes sharing lubrication from the engines.

An SAE10W30 oil suffices for year round operation.

Unlike the rubber-impeller waterpumps of most engines, Simplex engines use a combination of oval bronze rollers to pump water to the cooling passages. The rollers are far more reliable than rubber impellers and are capable of passing small solids without jamming. No thermostats are fitted, but according to Geoff Hall, son of Hardman & Hall’s co-founder, overcooling of the engines has never caused rapid engine wear.

In keeping with the theme of simplicity, the 6/7 and 10/12 have WICO impulse magnetos that are easily removed from the engines when not in use. The points can then be adjusted or replaced at home without the headache of the dampness that affects traditional battery-powered mechanical ignition when a boat is left afloat. The spark plugs are standard Champion units The low compression ratios of about 7:1 make for easy hand starting, although both engines are available with electric starting with belt-driven Hitachi starter motors that automatically switch to DC charging when the engine starts. The 12V system has a maximum output of 20amp.

Although only one carburettor jet is fitted, it is fully adjustable and because of the large flywheels the engines will idle down to around 200-300rpm.

Horsepower outputs for both models are rated on the old RAC (Royal Automobile Club) system, and in reality the brake horsepower figures are substantially higher. And as I’ve stated many times in Engine Talk, when choosing an engine, the maximum torque output is more important than maximum power.

In many ways the 6/7 model is like the Albin Cadet (5hp at 1600rpm), which was even fitted to fibreglass yachts in the 1970s. In a Contessa 25 , the Cadet provided more than adequate auxiliary power.

Developing 6hp continuous at 1000rpm or 7hp intermittent at 1200, the single-cylinder 6/7 weighs 130kg complete with a gearbox. The piston displacement is a whopping 774cc with a 98.4mm bore and 101.6mm stroke.

The maximum torque output is 43 Newton metres (Nm) at 1000rpm, 19% greater than Yanmar’s 636cc 2GM20 diesel, which develops 18.0hp at 3600rpm and its maximum torque at 3000rpm.

Measuring 743mm long, 467mm wide and 578mm high, the 6/7 is a fair lump of an engine and somewhat bulkier than the 2GM20, which is also 19% lighter.

Based on a standard displacement hull powering formula, the 6/7 model would suit timber launches up to 7.5m or full-keel yachts up to 9m. In my opinion this motor would be perfect for an H28.

A substantially heavier-duty motor than the 6/7, the twin cylinder 10/12 develops 10hp continuous at 1000rpm and 12hp intermittent at 1200. It displaces 1740cc, has a bore of 98.4mm and stroke of 114.3 and complete with gearbox weighs 300kg.

The 10/12 produces 86Nm of torque at 1000rpm, but measures 914mm long, 518mm wide and 673mm high, making it much bulkier than Yanmar’s 1496cc 3JH3E, which develops 39.4hp at 3800rpm and 100Nm at 2000. It also weighs 61% more despite having saltwater cooling compared to the Yanmar’s heat exchanger system.

Again using a standard formula, the 10/12 would suit timber launches up to 9m and full-keel yachts up to 11m.

According to Geoff Hall, the only problem with both engines has been corrosion of the cooling water passages due to owners not keeping these full of water. But in a yacht where most of the engine will be mounted below the static waterline, this is unlikely to occur. And with regular maintenance the engines should last 50 years!

As of August 2002 the manual start 6/7 retailed for $5800 and electric start $8150. The 10/12 retailed for $7600, although the additional $2350 for electric starting would be well worth the extra.

For more information, contact Leon Pompei 0419571788.