Review: Solé Mini-55 Marine Diesel Engine
Forty-odd years ago the Perkins 4.108 was the marine engine of choice for displacement cruisers to eight metres and yachts to 11 metres.
An automotive-based diesel, it developed 50.9bhp at a high 4000rpm from 1760cc. The indirect injection engine had a gear-driven camshaft operating pushrods for the eight overhead valves and was designed for heat exchanger cooling, though unusually raw (sea) water cooling for this cast iron engine was an option.
Peak torque was a reasonable 107Nm from 2200 to 2400rpm but unfortunately the Perkins 4.108 was no lightweight, coming in at 220kg dry with mechanical gearbox. That’s as much as some current 2.2-litre naturally aspirated marine diesel engines that develop the same power at only 3000rpm. And at 13.5L/h, the maximum fuel consumption was a tad high for the output.
Perkins 4.108 replacement
So what’s a suitable replacement for the long-discontinued Perkins 4.108? One choice is the Solé Mini-55 that develops comparable power from similar displacement at only 3000rpm thanks to its moderate-boost turbocharger. Indirect injection engines like the Mini-55 can suffer air starvation so slightly increasing the available air can produce not only substantial torque and power gains but also improve fuel efficiency. For example, the Mini-55’s fuel flow at its maximum output of 51.3bhp is a whopping 25 per cent less than the 4.108 yet peak torque is 17 per cent higher. And complete with mechanical gearbox, the dry weight is 14 per cent less.
The Mini-55 has a Mitsubishi-based industrial engine. I must confess a soft spot for Mitsubishi engines, having driven Mitsubishi utes for 33 years and tested plenty of Mitsubishi forklift trucks using petrol and diesel engines. The Spanish marinised Solé Mini-55 uses components from the naturally aspirated Mini-44 and three-cylinder Mini-33 so spares shouldn’t be an issue. Compared to the same-displacement Mini-44, the Solé Mini-55 is only 10 per cent heavier but develops 24 per cent more power and 16 per cent more torque for a 12 per cent increase in fuel flow at wide-open throttle, so Solé’s mild-boost concept is an absolute winner.
Design
The Solé Mini-55 marine diesel has a cast iron cylinder head and block with eight valves actuated by pushrods from a gear-driven camshaft. It has heat exchanger cooling and the compact turbocharger is mounted so that it’s very little higher than the rocker cover.
Sensibly – the Europeans know us yachties ain’t fools – the V-drive belt for the 50-amp voltage-regulated alternator and freshwater circulating pump is exposed, with the seawater pump located at the forward end of the block. The 1.7kW starter motor could be mounted a little higher but it’s still well away from any possible bilge water. The fuel filter/sedimenter is located aft where access isn’t so good but at least it’s mounted high, next to the air intake. The canister oil filter is mounted on its side to give minimal dribbling down the block when replaced.
Solé offers a range of mechanical and hydraulic gearboxes for the Mini-55, with the mechanical units being made by Japanese specialist Kanzaki and available in straight or seven-degree down angle outputs. The ratios range from 1.96:1 to 2.61:1, while the straight-output TM345 hydraulic gearbox has ratios of 1.54:1 to 2.47:1. In my opinion the 1.96:1 ratio is good for yachts and the deeper ratios for displacement cruisers. I would always opt for a mechanical ’box for yachts because the prop can freewheel under sail, reducing drag.
Complete with mechanical gearbox, the Mini-55 measures 871mm long, 537 wide and 607mm high, whereas with a mechanical Hurth ’box the 4.108 measured 893 x 589 x 669mm, so the 55 would take up less accommodation space. Of course with its greater torque output the propshaft may need enlarging and a coarser pitch prop fitted than with the 4.108.
The standard instrument panel has an analogue tachometer (thankfully to no more than 4000rpm) with digital hour meter plus an analogue coolant temperature gauge. An optional panel includes these plus an analogue oil pressure gauge and voltmeter. Warning alarms are included in both panels.
I suggest using an SAE 10W30 oil in cooler climates and SAE 15W40 in tropical conditions and changing the sump oil and filter every 100 running hours or six months as turbocharged engines need fresh oil. I also recommend propping the engine so that under normal running conditions it reaches 3100rpm, as turbocharged engines don’t like being overloaded.
The Trade-a-Boat verdict
Though I haven’t yet tried the Mini-55, 30-odd years ago I tested the Mini-34, a four-cylinder version of the current Mini-17 and Mini-29. Admittedly, at 1270cc it had a way smaller displacement than the Mini-55 but what struck me was just how smooth the engine was from fast idle upwards. Fitted to an Arends 33 cruising yacht it pushed us quietly and smoothly out to wide-open throttle. My substantially less flab than now remained fully intact.
I’m not saying the Mini-55 would be as smooth but it still has a small displacement for four cylinders so it’s unlikely to be significantly rougher. What I really like about the 55 is that is does everything the old 4.108 did but in a smaller, lighter and way more fuel efficient package.
For more on the SM105 visit Australian agents Headland Engineering or call (02) 9939 1966.
As the Solé Mini-55 has mechanical injection timing I recommend not running it continuously below 1800rpm or above 2500rpm. Running below 1800rpm for any length of time may result in cylinder bore glazing due to excessive fuel supply for engine load.
Solé Mini-55 specs
Engine type Four cylinder indirect-injection turbocharged diesel
Rated BHP/MHP* 51.3/52.0 at 3000rpm
Max torque (Nm) 125 at 2000rpm
Displacement 1758cc
Bore x stroke 78 x 92mm
Weight 189kg (dry w/gearbox)
* Brake horsepower/metric horsepower