Yanmar 6LY3 series

Yanmar's quick response

It had to happen! With increasingly tough exhaust emission laws and consumers in the recreational boating industry sold on electronically-managed diesels, it was a case of sooner rather than later that Yanmar added them to its popular range of turbo-intercooled in-line sixes.

Electronic management, as seen in the form of the Yanmar 6LY3 Series, offers a whole range of benefits, such as electrically-operated throttle and gearshift controls that eliminate the need for cables (especially important when upper and lower helm stations are fitted), increased fuel efficiency and more power and torque.

The main reason for these increases is that fuel injection spray timing is automatically altered according to engine revs and load, ambient temperature and fuel density. In mechanically-injected diesels the fuel spray timing is usually set for maximum efficiency in the peak torque band and when operating an engine below this band the spray timing is too advanced, while above the band it’s too retarded. This is why black exhaust smoke appears during critical load periods such as when the hull is overcoming its planing hump and excess fuel is being supplied to the cylinders.

While the mechanically-injected 6LY2A-STP is a beautifully responsive and lightweight engine for its output and will continue to be sold in Australia by Power Equipment as long as the current high demand continues, this 434hp (with 1hp equaling 746W) mechanically-injected engine can emit black smoke under certain load conditions.

For example, the first time I tried this engine in a twin-installation in a Fabio Buzzi 38 it ran very cleanly due to the fitting of two-speed ZF gearboxes which allowed the engines to be operated under relatively light loads until the hull was planing. But in a Black Watch 36 running single speed gearboxes where the engines were well loaded right through their rev ranges black smoke appeared when the helmsperson used the one ahead/one astern technique and when the hull reached the planing hump with the throttles well open.

The turbo-intercooled direct injection 6LY2A-STP has an intermittent rating of 434hp at 3300rpm.

The cylinder bore is 105.9mm and the piston stroke 110mm, so the engine is only slightly under-square.

By reducing piston speeds at high revs and in bobtail form (sans gearbox) the dry weight of the engine is only 515kg.

The maximum torque output is 1170Nm at 2500rpm, about 80 per cent greater than an 8.1lt petrol V8 and quite an achievement for an engine displacing only 5813cc.

However, as is common with mechanically-injected engines the torque curve is quite ‘peaky’ and, at 1700rpm, the output is 830Nm and 940Nm at 3300rpm.

Based on a standard prop power curve, at 2500rpm where the prop absorbs 208hp, the 6LY2A-STP consumes 39lt/h, rising to 71lt/h at the maximum continuous revs of 3100 where the prop absorbs 362hp.

The full load consumption at 3300rpm is 90lt/h.

The 6LY3-ETP develops 473hp at the same revs and from the same piston displacement, but the torque curve is much flatter with 1260Nm produced at 2400rpm.

At 1700rpm, the output is 910Nm and 1010Nm at 3300rpm.

Yanmar has also released a de-rated version of the 6LY3-ETP known as the 6LY3-STP, which develops 374hp, two per cent up on the mechanically-injected 6LYA-STP.

The bobtail dimensions of the 6LY2A-STP are 1274mm long, 708 wide and 709 high, whereas the 6LY3-ETP measures 1300 x 801 x 777mm, so it’s significantly bulkier. The weight has risen 24 per cent to 640kg - a hefty increase considering the power and torque gains.

However the weight increase is understandable, especially when you consider the re-engineering.

The engine still has pushrod actuation for the 24 valves, but the flywheel housing has been ‘upgraded’ to support larger gearboxes and the increased power/torque ratings. The crankshaft torsional damper has been upgraded and a new damper has been fitted to the fuel pump drive.

The fuel injectors each have two springs and a hydraulic injection timer and electronic governor are now used. Both the main and bypass lubricating oil filters are mounted up near the injectors and an intake heater is standard.

The cast aluminium intercooler and exhaust manifold are now integrated and, for reliability, the alternator and freshwater circulating pump are now driven by a double vee-belt with a cover over the pullies for safety.

The starter motor has been uprated from 2.5 to 3.0kW, but the standard 12V 80-amp alternator remains unchanged.

The engine management computer box is mounted on the engine almost at rocker cover level and well away from any bilge water.

The system records full run-time engine data including engine revs percentage, hours, battery voltage, coolant temperature, turbocharger boost and oil pressures, and fuel flow.
There are also 16 alarm sensors and any operating problems with the engine may be assessed using the diagnostic facility.

Matched to the engine power and torque characteristics, a Kanzaki KMH hydraulic gearbox adds only 78kg to the bobtail weight and increases overall engine length to 1357mm. The reduction ratios are 1.55:1, 2.04:1 and 2.43:1 in both ahead and astern.

For more details on the new engines, contact Michael Blair at Power Equipment on (03) 9764 0711 or email power.equipment@yanmar.com.au