Review: Solé SM105 Marine Diesel Engine

Some time ago I reviewed a seven-tonne Mitsubishi Grendia FD70N forklift truck for Australasian Transport News, the same publishers as Trade A Boat and TradeBoats.com.au. That truck had clever features such as a two-speed power shift in forward and reverse. But what really grabbed my attention was the naturally aspirated S6S straight-six diesel powering it. From idle to well up in the rev range there was absolutely no vibration – I’ve tested plenty of six-cylinder diesels but frankly none as smooth as this engine. My flab sure remained intact that day!

After that engine review I searched online for more on the engine. I uncovered a wealth of operating info but couldn’t find a company that sold the S6S as a loose unit – until I came across Solé’s website. Solé is a Barcelona company that has been marinising Mitsubishi, Nissan and Deutz industrial diesels for as long as any old fart like me can remember. And there it was – the SM105, a marinised version of the beaut S6S.

In its industrial form the S6S develops 90.8bhp at 2300rpm, with 290Nm at 1600rpm. Like most industrial diesels designed to meet strict exhaust emission regulations (even for forklifts in the US) it has indirect injection and glowplugs for easier cold starting; these are needed as the compression ratio is a fairly high 22:1. But incredibly for a diesel of only five litres it has a 9000-hour overhaul interval and user reports have claimed twice that without rebuilding the engine. In recreational repowers I’d be pushing up daises long before this engine was worn out!

In marine diesel engine form with heat-exchanger cooling the S6S develops 93.7bhp at 2500rpm with a continuous rating of 85.7bhp at the same rpm. So it’s strictly for displacement hulls, where bottom-end torque output is way more important than top-end power.

Solé has done a good job of marinising the S6S. All regularly maintained components are easily reached and there’s a 95-amp alternator as standard. The oil sump is deep enough to allow for 25-degree intermittent heel port and starboard, so the engine would also suit larger motorsailers in addition to displacement cruisers.

A choice of hydraulic gearboxes is available but the default unit is the TM93A that has a choice of 2.09:1 to 2.4:1 reduction ratios and an eight degree-down angle at the output flange. This is important as most displacement cruisers have shaft angles of around eight degrees, so the engine can be mounted parallel to the waterline. This makes accessing the aft end of the engine easier and you’re more likely to be able to completely drain the sump when changing the oil and filter.

Solé doesn’t mention suitable oil viscosities but I suggest a diesel-specific SAE 30 mono grade for temperate climates and SAE 15W40 for tropical conditions. I also suggest changing the oil and filter every 200 running hours or annually.

With the TM93A ’box the SM105 is 1302mm long, 660mm wide and 770mm high. Suitable repower hulls would be the Island Gypsy 32 and Grand Banks 32. These were originally available with either the four-cylinder Ford 80 or six-cylinder Ford 120. I made coastal delivery trips of Island Gypsy 32s for Harvey Halvorsen in the early 80s and found the 120 was overkill while the 80 was a tad underpowered for offshore cruising.

What hulls are most suitable?

Developing maximum power at 2500rpm from around 3.9 litres, the 80 weighed almost as much as the SM105 with slightly less torque, so the SM105 would be a nice compromise between the 80 and 120, although the engine bearers would need lengthening to accommodate the additional 200mm or so engine length over the four-cylinder unit. Frankly, the surgery would be worth it to swap substantial vibration through the entire hull to virtually no vibration.

Alternatively, if the boat had the Perkins 4-236 – which develops 76bhp at 2250rpm and 250Nm at 1600rpm and weighs almost as much – the SM105 would provide that extra bit of performance without opting for a Perkins 6-354 which is a substantially heavier engine.

Another suitable hull for the SM105 is the Halvorsen 30 where the engine would neatly replace the old Chrysler Crown petrol inboard, though that side-valve unit has a relatively low height so the engine compartment height would need to be raised, plus you need keel cooling with a dry exhaust instead of the standard heat exchanger. Still, the SM105 is about the only diesel that would replicate the almost vibration-free running of the Crown.

As the engine has mechanical fuel injection, Mitsubishi agents recommend five minutes of no-load warming from cold but no more than 10 minutes or the cylinder bores could glaze. The lubricating oil needs to be circulated then the engine worked, the way most diesels should be treated. The SM105 develops maximum torque at 1400rpm so I recommend not running it continuously below 1200rpm, while 2200 would be my maximum continuous cruising revs.

The Trade-a-Boat verdict

Not only is the Sole S6S marine diesel incredibly smooth but it’s way cleaner running than the old direct-injection Ford and Perkins engines. While testing the Grendia forklift I noticed there was no smoke on cold start-up or when the engine came under load such as quickly raising a stacked pallet or accelerating with a load on the forks.

In boat terms, this means your passengers can sit on the aft deck in following seas without you needing a bucket and mop handy to clean up the vomiting from inhaling exhaust fumes that occurred with the old engines. I know this personally from charter-skippering an Island Gypsy 36 powered by twin 120s on Sydney Harbour.

For more on the SM105 visit Australian agents Headland Engineering or call (02) 9939 1966.

Solé SM105 sea trials and statistics

1000rpm produces 290Nm of torque with 6.7bhp absorbed by prop and with fuel burn of 2.0L/hr 

1800rpm produces 290Nm of torque with 40.2bhp absorbed by prop and with fuel burn of 8.0L/hr

2500rpm produces 260Nm of torque with 93.6bhp absorbed by prop and with fuel burn of 19.8L/hr

Solé SM105 marine diesel specs

Solé SM105 price: $27,600 + GST

Engine type Six-cylinder indirect injection marinised diesel

Rated BHP/MHP* 93.7/95.0 at 2500rpm

Max torque 300Nm at 1400rpm

Displacement 4996cc

Bore x stroke 94x120mm

Weight 474kg (dry w/ gearbox)

* Brake horsepower/metric horsepower