Yanmar 2GM

Released in the late 70s, the Yanmar 2GM was the forerunner of the 2GM20 and developed 13hp (based on 1.0hp equaling 746W) at 3300rpm with a maximum continuous rating of 11.8hp at 3200rpm.

Displacing 586cc, this twin-cylinder indirect injection diesel with pushrod OHV operation had a 'square' bore/stroke design of 72mm and, complete with mechanical gearbox, weighed 100kg. As the 2GM was designed from the start as a marine engine, it had thermostat-controlled raw (salt) water cooling, which, according to Yanmar agent Richard Minard was very reliable due to its inherent simplicity.

Unusually, the seawater cooling pump was driven by a single vee-belt from the crankshaft and, although electric starting was standard, it was possible to start the 2GM by hand using a handle that slotted onto the forward end of the camshaft. An individual decompression lever was fitted atop each cylinder although, with a 23:1 compression ratio, the 2GM required a very strong person to keep the flywheel spinning when the compression levers were closed.

As Yanmar brought its small engines into line with increasingly tough exhaust emission laws, the 2GM was fitted with heat exchanger cooling, which added about 15kg to the engine's dry weight.

With the development of the 636cc 2GM20, which was essentially a bored-out and stroked version of the 2GM and fitted with a lighter flywheel to allow for higher engine revs, the 2GM was relegated to commercial usage and fitted with a heavy-duty mechanical gearbox, which added about 40kg to the dry weight, or 155kg in total. This model was known as the 2GMFY and last year the 2GM20 was replaced by the three-cylinder 3YM20 reviewed last year in Trade-A-Boat.

For recreational markets, the 2GM was replaced by the twin-cylinder 2YM15, which like the 3YM20 has standard heat exchanger cooling. Unlike the 2GM and 2GMY, these TNV industrial-base engines comply with US EPA and EU exhaust emission regulations

THE 2GM LIVES ON
Last year Yanmar introduced the 2GMY, which is a raw water-cooled version of the 2GMFY and has raised hand starting (in addition to electric starting), enabling a handle to be fitted fore or aft. From my time spent in the Australian Merchant Navy more than three decades ago I can tell you that hand-starting the ubiquitous Lister diesels we used for lifeboats and fire pumps was made much easier with the raised crank handle, which allowed us to put some muscle into spinning the flywheel before closing the decompression levers.

The 2GMY develops 14.8hp at 3600rpm with a continuous rating of 13hp at 3300rpm, and has a dry weight of 140kg. Compare this output to the 2YM15, which develops 13.8hp at 3600rpm from 570cc. With standard heat exchanger cooling but no provision for hand starting, the 2YM15 has a dry weight of 113kg.

Although Yanmar doesn't quote torque figures for the 2GMY, based on the 2YM15 and the 2GM20, which developed 17.4hp at 3600rpm, the peak output should be around 34Nm in the 2000rpm range.

Complete with straight-output mechanical gearbox, the 2GMY is 713mm long, 454mm wide and about 580mm high to the top of the rocker cover. The 2GMFY was 606mm high, including the heat exchanger expansion tank filler cap but, at the time of writing this review, no height measurement was available for the 2GMY. If you're re-powering an existing hull from a Yanmar 1GM10, the 2GMY has its exhaust on the starboard side so the same exhaust hose route can be used, but with larger diameter hosing to accommodate the higher exhaust gas flow.

In comparison, with mechanical box the 2YM15 is 613 x 463 x 528mm, or 600mm high with the optional U-mixing exhaust elbow. Minard says the 2GMY would really suit a small launch and, from my testing of a 2GM in a Spacesailer 24 keelboat, the 2GMY should give hull speed for full displacement launches in the six to seven-metre range.

ON THE WATER
Five years ago my friend Linda was searching for a Spacesailer 24 suitable for coastal cruising and pottering around Lake Macquarie.

Linda looked at several boats but settled on the late 70s model she owns because it had a Yanmar diesel.

Since owning Albatross, Linda has only had to fit a new waterpump impeller, alternator, and exhaust mixing elbow to the original equipment, raw water-cooled 2GM.

She changes the engine oil and filter once a year and uses SAE 15W40 diesel engine oil which is suitable for operation in all ambient temperatures.

We tested the 2GM with a clean hull and, despite its age, the engine was capable of reaching over 3000rpm without blowing any exhaust smoke. The engine started instantly hot or cold and idled in gear at 700rpm. At about 1200rpm, there was some harmonic vibration through the hull but above 1500rpm it ran as smooth as some small three-cylinder diesels I've tested.

Above 2500rpm, the vibration levels were comparable to a four-cylinder diesel, thanks to the large diameter flywheel. And only above these revs was there any diesel smell from the exhaust.

Driving a 13 x 10-inch fixed-pitch three-bladed prop through a 2.21:1 reduction ratio, the 2GM easily pushed our 2.3-tonne total. The best cruising revs were around 2000, where according to the Raymarine paddlewheel log, Albatross averaged 4.7kt with the 2GM consuming just 0.8lt/h. Being raw water cooled with the thermostat opening at about 70 degrees, the 2GM should be operated continuously at or above 2000rpm to prevent glazing the cylinder walls.

For more details on the 2GMY, contact Michael Blair at Power Equipment on (03) 9764 0678 or email power.equipment@yanmar.com.au