Yanmar 4JH4

A four-cylinder version of the Yanmar 3JH4 reviewed recently in Trade-A-Boat, the 4JH4 uses a Netherlands-built TNV industrial base engine to provide significantly more torque and similar power (but at 800 fewer rpm) than its reliable 4JH3 counterpart. As with this engine, the 4JH4 has direct injection compared to indirect injection for the 3JH4, but at 88 x 90mm the bore and stroke remain unchanged.

Displacing 2190cc, the 4JH4 develops 53.1hp (at 1.0hp = 746W) at 3000rpm compared to 55.0hp at 3800rpm for the 1995cc 4JH3. However, the biggest improvement over the 4JH3 is the maximum torque output and the rpm at which this is produced. Whereas the 4JH3 produces a peak of 122Nm at 2000rpm, dropping to 102 at 3800, the 4JH4 produces 155Nm at 1900rpm diminishing to 126 at 3000.

Through the rev range there's a similar torque output difference. At 2000rpm the 4JH4 produces 153Nm, and at 2500rpm 141, compared to 119 at the same rpm for the 4JH3, which produces 113 at 3000rpm. By 3500rpm the 4JH3's torque has dropped to 104Nm.

HORSEPOWER VERSUS FUEL CONSUMPTION
Based on a standard displacement hull prop power curve, at 2000rpm the 4JH4's prop absorbs 14.7hp and the fuel consumption is 3.5lt/h, whereas at the same rpm the 4JH3's horsepower is 8.0 and consumption 2.2lt/h. So at these revs, the 4JH4 develops 84 per cent more power for 59 per cent greater fuel usage.

At 2500rpm the 4JH4's figures are 28.2hp and 6.3lt/h compared to 16.8 and 3.9 - percentage differences of 68 and 62 - while at 3000rpm the prop absorptionhp is 51 and usage 11.9 compared to 26.1 and 6.0 - percentage differences of 95 and 98.

At 3800rpm and 52.9hp the 4JH3 uses 12.2lt/h, giving percentage differences of four and two per cent. So from 3000–3800rpm the 4JH3 is slightly more fuel efficient - a different story to the 3JH4 versus its 3JH3 counterpart.

Released locally in 2001, Volvo Penta's D2-55 is based on a Japanese Shiibaura industrial diesel and develops 55.0hp at 3000rpm from its four-cylinder 2217cc powerhead. As with the 4JH4, it has pushrod-actuated overhead valves and freshwater (heat exchanger) cooling, but indirect injection and cold-start glow plugs. The starter motor output is 2.0kW compared to 1.4 for the 4JH4, but the additional power is needed to overcome the much higher compression ratio (23.3:1 compared to 17.7:1) of the indirect injection engine. Were decompression levers and a raised hand-crank fitted, the Yanmar could be started by hand, whereas handstarting the Volvo Penta would be way too much of an effort!

Unlike the 4JH4 the D2-55 has more of a conventional naturally aspirated diesel torque curve, peaking at 135Nm at 2350rpm with 133Nm being produced at 2000rpm and 129 at 3000rpm.

Although a direct horsepower-to-fuel usage comparison is not possible from the specs supplied by Volvo Penta, at 2600rpm where the prop absorbs 34hp, the D2-55 uses 8.0lt/h; and at 3000rpm and 52.8hp 12.5lt/h - so the D2-55 develops 21 per cent more usable power for a 27 per cent increase in fuel flow at cruising rpm and four and five per cent respectively at Wide Open Throttle.

Although "cleaner", indirect injection does not provide the power per litre of fuel of direct injection, and these percentage differences are to be expected.

Yanmar's 4JH4 is lighter and smaller than both its 4JH3 counterpart and D2-55 competition. To compare the engines directly, all are listed here with down-angle output flange mechanical gearboxes, which in most displacement hulls allow for a zero-degree fore and aft installation angle for a longer engine lifespan.

Whereas the 4JH3 is 890mm long, 563 wide and 619mm high, with the same KM35A box the 4JH4 measures 864 x 539 x 617mm. The standard cover for the seawater cooling pump and alternator drive belt adds 21mm to the overall width. In comparison, with an MS25A box the D2-55 is 917mm long, 544 wide and 691mm high.

At 213kg with the KM35A, the 4JH4 is four per cent lighter than the 4JH3 and 12 per cent lighter than the D2-55. And Yanmar says the 4JH4 is also eight per cent lighter than the Kubota-based 2197cc indirect injection Nanni 4.220HE, which develops 49.3hp at 2800rpm and measures 947 x 562 x 627mm.

BETTER GEARBOX CHOICE
The 3JH4 is available with two mechanical boxes (mentioned in the 3JH4 review) and the SD40 saildrive, but the 4JH4 goes two better with the optional KM4A1 and ZF30M boxes.

Although still a mechanical box with cone clutch, the KM4A1 is a heavier-duty unit and has a choice of four ratios from 1.47:1 ahead and astern to 3.30:1, while the ZF30M is a mechanical multiplate clutch box designed more for displacement-hulled cruisers and heavy-displacement cruising yachts and has ratios of 2.15:1 ahead and 2.64:1 astern.

These boxes add 15kg to the 4JH4 weight with KM35A box, and the dog-clutch SD40 saildrive with 2.32:1 ratio ahead and astern adds 16kg.

All other aspects of the 4JH4 are the same as its 3JH4 counterpart, with the engine components such as the engine-oil dipstick, canister-oil filter, water-separating fuel filter, starter motor and alternator in the same location. The voltage-regulated 60amp alternator may be swapped for an 80amp unit, or alternatively a second alternator can be fitted opposite the standard unit.

For cruising yachts with a hull speed of 8kt at WOT, Yanmar recommends using a 19.7 x 11.8in prop for the KM35A's 2.33:1 ratio and a 19.7 x 13-incher for the 2.64:1 ratio, both props having three blades and blade area ratios of 0.43. The ZF30M box needs a 19.7 x 11-incher.

Yanmar's switch to industrial-base engines in its smaller diesels has certainly proved beneficial for marine applications. The TNV-based engines are compact, light, torquey and fuel efficient for their outputs, and correctly propped should provide years of motoring pleasure in yachts and cruisers alike.

For more information on the 4JH4, contact Michael Blair at Power Equipment, tel (03) 9764 0711 or email power.equipment@yanmar.com.au