Common Railing: Talking Torque with Andrew Norton

The original concept of common rail was to inject fuel at high pressure (up to 26,000psi or 1770bar) via electronically controlled fuel injectors. A way finer fuel spray combined with direct injection into the combustion chambers ensured engines would meet current and upcoming exhaust emission regulations without opting for the more expensive electronically-controlled unit injectors favoured by some USA diesel engine manufacturers.

In comparison, mechanically-controlled diesels have injection pressures of around 2000psi or 136bar and provide nowhere near the precise injection control of common rail engines. Back in the sixties, Lister achieved some low-emission results, despite running direct injection, through the use of mechanical unit injectors. However, these were expensive to produce, so since then most manufacturers of mechanically-controlled diesels have used in-line or rotary injection pumps. 

The 6LY440 is the second largest inline six in the recreational engine line-up. It's also available as a 400, which develops 393 brake horsepower at the same rpm.

THE NITTY GRITTY

Unlike Yanmar's mechanically-controlled SOHC Land Cruiser 100-based 4.2-litre 6LPA-STP2, the 6LY440 has traditional marine engineering, with a gear driven camshaft actuating rockers via push rods. Valve clearance adjustment should be simple too, as with most push rod engines where just a feeler gauge and adjusting spanner are needed instead of finicky shims with the Toyota-based 6LPA-STP2 engine. Why Toyota does this is a mystery when other Japanese engine manufacturers use the spanner and feeler gauge system, even with SOHC engines.

The 6LY440 has a relatively deep lubricating oil sump that allows for a maximum operating tilt angle of 30 degrees to port or starboard or 25 degrees nose up, allowing for a wide range of operating conditions. The thermostat starts opening at 71 degrees and is fully opened by 85 degrees ensuring the engine runs efficiently without stressing the cylinder head gasket. 

A sump oil-level dipstick is mounted either side of the engine for better access in twin installations. Yanmar states the maximum oil capacity is 20 litres, so the engine should resist oil dilution and sludging well between oil and filter changes. Twin oil filters are fitted to starboard. Yanmar doesn't mention the recommended oil viscosity, but in line with other common rail engines in its range I suggest using a diesel-specific SAE15W40 oil, and change the oil and filter every 100 to 200 running hours (depending on how frequently the engine is used) or every six months. Clean oil is a cheap price to pay for engine longevity.

As fuel density can vary depending on where it's sourced, Yanmar rates the 6LY440 to run on a fuel density of 835 to 845 grams per litre, so the engine is more than capable of running on the poor-quality fuel Aus has to suffer without needing to de-rate engine output. Way better than when Yanmar, like most European diesel engine manufacturers, rated outputs based on 860 grams per litre. Yanmar recommends fitting a RACOR water separating fuel filter between the fuel tank and fine filter mounted on the starboard side of the forward engine end, the last line of defence before the high-pressure fuel pump. It's also very specific about using FKM (fluorine-contained) rubber fuel hoses to prevent permeation of fuel through the hose.

The 6LY440 has a massive cooling-system capacity of 20 litres to reduce engine overheating in tropical climates.

Standard are a 12-Volt 3kW starter motor and a 120amp voltage regulated alternator, the latter again made by Denso. Either a second 120amp or 24-Volt 45amp alternator may be fitted. Yanmar recommends using 12-Volt 200amp/hour starting batteries with 900 CCA (cold cranking amps) capacity. Alarms are fitted for fuel and water temperature overheat and low engine oil pressure with information displayed on Yanmar's VC10 vessel control system which has menu selection accessed by up, down, left and right arrows. VC10 is interlinked with Yanmar's drive-by-wire throttle and gear shift control for precise boat handling.

Yanmar offers the 6LY440 (and 400) with a choice of eight-degree down angle and 12-degree V-drive hydraulic gearboxes. 

The eight-degree unit has gear ratios of 2.43:1 ahead and astern, up to 1.55:1. The box has a 2.8-litre oil capacity. Overall dimensions for the 440 with this box are 1440mm long, 740mm wide and 873mm high, or 255mm from the gearbox base to engine bearers and a distance of 950mm between fore and aft mounting feet. The COG (centre of gravity) is 368mm aft from the forward feet. 

The V-drive box has ratios of 2.43:1 ahead and astern up to 1.24:1 and a 7.5-litre oil capacity. The overall engine/box combo dimensions are 1440mm long, 829mm wide and 947mm high, with 378mm from the gearbox base to mounting feet. The engine mounting feet are 1018mm apart and COG is 401mm aft of the forward mounts.

Yanmar distributor Power Equipment provided me with two examples of boats powered with the 6LY440. The first was an 11.6m fibreglass planing hull, displacing nine tonnes and powered by a single 440 driving through the eight-degree boat and having a 2.43:1 reduction ratio, that reached 19kts at Wide Open Throttle. Note how deep the gear ratio is, giving maximum prop rpm of 1360 because it's unlikely at 19kts the hull is fully planing. 

The second was an 11m Black Watch 36, which ran twin 440s, 21 x 28-inch four bladed props and 2.04:1 reduction ratios and an efficient maximum prop rpm of 1620. This rpm is an effective compromise between efficient prop thrust without creating excessive drag had the deeper reduction and larger props been used.

The 11-tonne 36 cruised at 25.4kts using 67lt/h per engine and reached 30kts at WOT using 88lt/h. The WOT speed is quite an improvement over the twin 6LY2-STE engines I tried in a Black Watch 36 several years ago, which reached 27kts and did blow some black exhaust smoke coming out of the hole. One thing I do remember was how smooth the engines were, with none of the rumble that emanates from some truck-origin engines in the same power range I've tested. 

THE WRAP

Much as I like the simplicity of mechanically-controlled diesels, I must confess that having real-time fuel flow, range to empty and electronic engine synchronisation are really nice. The drive-by-wire controls also allow for much easier shifting and more precise boat control.

The other aspect of the 6LY440 is that it's a specific marine engine, not a marinised truck engine. The peak torque band is right where needed for planing a hull and returning maximum fuel efficiency, not down below the planing zone as with some of the competition. And of course the 6LY440 meets all current exhaust emission regulations, which although may not be so relevant in Aus does mean the engine is cleaner running and less likely to make passengers sick when trolling offshore in following seas.

Google Yanmar Marine Diesels, enter Dealer Locator, click on the type of dealer (marine) and enter your region and postcode to locate your nearest dealer.

SPECS:

YANMAR 6LY440

Engine type Straight-six turbocharged after-cooled common rail diesel 

Rated BHP/MHP* 246.6/250.2 at 3,800rpm

Max torque 1220nm at 2100 to 2500rpm

displacement 5813cc

Bore x stroke 105.9 × 110mm

Dry weights

8-degree down angle 661kg

12-degree V-drive 693kg

* Brake horsepower/metric horsepower or PS.