Iveco 4021M20 and 4021M30

The smallest marine diesel engines from Iveco are designated the 4021M20 and 4031M30. These lightweight heat-exchanger-cooled diesels are based on industrial engines built by Lombardini and share the same 75mm bore and 77.6mm stroke, the former having two cylinders and the latter three.

Engine outputs are 'pleasure duty' or 'A' rated with Wide Open Throttle (WOT) operation restricted to ten per cent of any one period and total operating hours of no more than 300 per year, unlikely to occur when the engines are used as yacht auxiliaries. Iveco rates these engines after 50 hours of 'running in' have been completed.

LET'S TORQUE OUTPUT
While the torque curves are not as flat as Yanmar's TNV industrial-base diesels, the Iveco engines develop more torque at lower revs than Yanmar's 2GM20 and 3GM30, which were specifically developed as marine engines.

For example, the 636cc 2GM20 developed 17.4hp at 3600 revs and produced a peak torque output of 37.5 Newton metres (Nm) at 2800 revs. Complete with heat exchanger cooling the 2GM20 weighed 114kg.

But the 686cc 4021M20 develops 19.7hp at the same revs and 44.5Nm at a low 2200 revs, making it better suited to pushing yachts than the Yanmar.

Replacing the 2GM20F and already reviewed in Trade-A-Boat, the 854cc three cylinder 3YM20 develops 20.5hp at 3600 revs and 50.5Nm from 2200 to 2500 revs, but weighs 120kg.

Reviewed a while ago in Trade-A-Boat, Beta Marine's Kubota-based 719cc three cylinder BD722 develops 22.7hp at 3600 revs and 43.2Nm at 2600 and with heat exchanger cooling weighs 106kg.

The 1028cc 4031M30 develops 29.6hp at 3600 revs and 69Nm at 2400 revs, whereas Yanmar's 954cc three cylinder 3GM30F developed 26.8hp at the same revs and 55Nm from 3000 to 3200 revs but weighed 137kg.

Again, this engine has been replaced by the 1115cc 3YM30 (reviewed by both Geoff Middleton and myself), which develops 28.6hp at 3600 revs and 69.5Nm at 2000 to 2500 revs and weighs 133kg.

GOOD FUEL ECONOMY
The Beta and Yanmar engines mentioned above all have indirect fuel injection to provide a 'clean' air/fuel burn and reduce exhaust emissions and the baby Ivecos are no exception.

Based on a standard prop power curve (not supplied by Iveco), at 2400 revs the 4021M20's prop can absorb 9.4hp while the fuelflow is 2.1lt/h (compared to 6.0hp and 1.8lt/h for the 3YM20 and 8.1hp and 1.9lt/h for the BD722). At 3000 revs the Iveco engine handles 12.6hp of prop demand and uses 3.0lt/h, whereas the 3YM20's figures at these revs are 11.8/3.0 and the BD722's 13.7hp and 3.1lt/h. At 3600 revs the 4021M20 uses 5.1lt/h compared to 5.2 for both the Yanmar and Beta engines.

Although now discontinued, at 2400 revs the 2GM20's prop demand was 5.4hp and fuelflow 1.5lt/h, at 3000 revs 10.6hp and 2.6lt/h and at WOT the engine used 4.5lt/h.

Again using a standard prop power curve not supplied by Iveco, at 2000 revs the 4031M30 can absorb 10.7hp at the prop using 2.4lt/h whereas at these revs the 3YM30's prop demand power is 5.1hp and fuelflow 1.1lt/h. At 2500 revs the figures are 15.4hp and 3.4lt/hcompared to 9.2/2.2 for the Yanmar and at 3000 revs 21.7/4.9 and 16.1/3.9 respectively. At WOT the Iveco uses 7.3lt/h and the Yanmar 6.7.

Compare these figures to the now-discontinued 3GM30F, which had a prop demand of 4.5hp at 2000 revs and fuel usage of 1.3lt/h, at 2500 revs 9.1hp and 2.3lt/h and at 3000 revs 16.1 and 3.7. At WOT the 3GM30F used 6.5lt/h.

COMPACT BUT WELL-EQUIPPED
Both Iveco engines have the same 488mm width and 522mm height and complete with TCM40A gearbox the twin cylinder engine is 568mm long and the three cylinder engine 643mm, with respective weights of 98 and 111kg. The twin cylinder unit would make an ideal re-power engine for older yachts such as the Compass 28, which in its day was commonly fitted with single cylinder Yanmar YSE12.

Complete with gearbox, the BD722 measures 630mm long, 438 wide and 526mm high, while the 3YM20 is 693 x 463 x 528mm. The 3TM30 is 715 x 438 x 526, so the 4031M30 is a compact engine for its output.

To ensure lube oil pressure does not diminish when a hull is pitching in heavy headseas, both engines are designed to handle up to 25º continuous inclination fore and aft and 25º of tilt while motorsailing. The 14 volt 60 amp voltage-regulated alternators are mounted high on the engine blocks and as far away as practicable from any bilgewater, while a front power take-off pulley and a lube oil sump evacuation pump are standard. An easily-removed plastic shroud covers the fuel pump and seawater cooling pump (which has a sacrificial anode) drives and unusually for engines this small the camshafts are belt-driven.

Although I would prefer chain-driven camshafts for reliability there's no denying belt drives are a lot quieter and generally troublefree providing they are changed at the manufacturers' specified intervals.

The heat exchanger header (expansion) tanks are no higher than the rocker covers resulting in relatively low engine heights and have dry element air cleaners, while air intake silencers are standard. The exhaust manifolds are freshwater cooled with saltwater injection into the stainless steel exhaust elbows.

For more details on the Iveco 4021M20 and 4031M30 contact Stewart Butler at Lees Industries, tel (07) 3390 5522 or email leesinda-sales@powerup.com.au