Yanmar 6LY2-STE

Following the successful introduction of its 6LP range of engines in both shaft and sterndrive versions, Yanmar could have been forgiven for taking a breather this year. That's not been the case, however. Indeed, the Japanese marine diesel expert has kept its hi-po ball rolling into 1999 with a bored-out version of the popular 5184cc turbo-intercooled 6LYA-STE model.

The new powerplant, known as the 6LY2-STE, not only retains the smaller counterpart's compact external dimensions but also develops another 70hp, taking the total to 420hp. The piston displacement is 5813cc (bore 105.9mm and stroke 110mm) and like the 6LYA-STE model it has direct injection and 24 valves with reliable pushrod actuation.

Though lacking the precise electronic engine management of diesels such as Volvo's TAMD72P/EDC, which develops 430 crankshaft horsepower at 2600 revs from 6.7lt, the 6LY2-STE scores by having a bobtail (no gearbox) weight of only 515kg incredibly light for a 420hp diesel!

According to the manufacturer, compared to the TAMD72P/EDC the Yanmar is a whopping 42% lighter. And even against the conventional TAMD63P, which develops 370 crankshaft horsepower at 2800 revs from 5.5lt, the Yanmar weighs 31% less.

Initially, I thought that the Yanmar's light weight might come at the expense of midrange output. But according to Yanmar's performance graphs, the 6LY2-STE still develops 410hp at 2700 revs and a healthy 1110nm of torque at 2500 revs.

Boatbuilders who used to fit US-origin powerplants in the smaller models of their planing hull cruiser range have found the new and much lighter Yanmars an excellent alternative to the heavier OEtraditional' brands. Locally, Stebercraft of Taree (NSW) is one such company and believes it has made the right move offering Yanmars as standard equipment in its 1050 cruiser released a couple of years ago. Caribbean and Black Watch also offer Yanmars as OEM fitment.

Though midrange fuel consumption does tend to work out higher than electronically-managed diesels, where the fuel injection timing is always correct for a given set of revs and load, the Yanmars' lighter weight more than compensates for the additional fuel needed to be carried. And with much simpler component layout around the engine it has a much lower profile than electronically-managed diesels.

For example, without gearbox the 6LY2-STE measures 1275mm long (1316 with box), 708mm wide and 709mm high from sump to heat exchanger. In comparison, a Volvo TAMD63P measures 1085mm x 612mm x 892 mm, while the TAMD72P/EDC measures 1260mm long and 765mm wide, but stands an imposing 962mm high! That's a big difference...

One of the major attractions of the engine (especially in the US market) is its suitability as a replacement for petrol V-eights. The nearest petrol engine in power, the 400hp MerCruiser 8.2lt MPI Inboard, measures 1219mm long including gearbox, 813 wide and 559 high.

So, with a twin Yanmar installation there'll actually be more room between the engines for regular maintenance, though the diesels are a little higher. When it comes to diesel engines of similar output, the Yanmars are considerably smaller than their opposition. In fact, one oft quoted statistic is that three 6LY2s can be installed in the same space as a pair of some of their larger-sized competitors!

With its lack of plug-in diagnostic facilities the 6LY2-STE would probably be no cheaper to service than an electronically-managed diesel, but repair costs will likely be lower down the track. The inline design has great servicing and repair access, with components such as the injectors easily reached, and the starter motor sited above engine bearer level and away from bilgewater.

Compared to big block petrol V-eights, fuel economy is in another class. For example, at maximum torque the specific fuel consumption is around 70lt/hr, while at maximum revs (3300) it's 90lt/hr. But the nearest petrol competition, again the 8.2lt MPI Inboard, consumes more than 120lt/hr at Wide Open Throttle. Yanmar is confident the new powerplant will offer fuel consumption gains when compared to its existing diesel competitors.

The 6LY2-STE features a massive 80 amp alternator and freshwater (heat exchanger) cooling. It comes with the option of three gear ratios: 1.58:1, 1.92:1 and 2.26:1. The 1.58:1 ratio is ideal for planing hulls previously petrol-engined and at 3300 revs these ratios give prop revs of 2090, 1720 and 1330.

When I questioned the Australian distributors of Yanmar diesels, Power Equipment Pty Ltd, about why Yanmar chose not to opt for electronic engine management, the answer was reliability.

Considering Yanmar's long-running involvement with the commercial fishing and small ship industries, reliability has always been number one with the company. And from my testing of marine engines for the commercial fishing industry, that emphasis has paid off over the years. Most pro fishos I've interviewed said that Yanmars were the most reliable diesels they'd ever operated, an experience also common among yachties and owners of displacement cruisers.

For commercial operators, who clock up thousands of hours on a motor, the midrange savings made by opting for electronic engine management would probably pay off. But for most recreational boat owners, the Yanmar 6LY2-STE is an excellent compromise between a thirstier petrol V-eight and the more expensive electronically-managed diesel.

Despite its fixed injection timing the 6LY, through careful combustion chamber design, complies with the IMO Bodensee (Lake Constance, Germany) exhaust emission regulations, and like all Yanmars it has the benefit of eight decades of marine engineering.

Yanmar also manufactures all components that go into its diesels, right down to the fuel injectors, resulting in total quality control over the way its motors are built.

There's no doubt this Yanmar slots perfectly into the market for which it was designed.