Review: Sole Mini 29 Marine Diesel Engine
It’s amazing how adding another cylinder can significantly increase maximum torque and power outputs for very little weight gain.
The Mini-29 is a fine example. A three-cylinder version of the Sole Mini-17, it develops 47 per cent more torque and 71 per cent more power at the same revs, yet is only 11 per cent heavier. Admittedly, peak torque output takes 500 extra revs but considering the torque and power gains for the additional weight this isn’t a major problem.
What is important is that the small weight gain means the 29 is a viable repower option for a long-keel cruising yacht such as a Clansman 30. Unlike the old single-cylinder diesels originally fitted to this model – which actually weighed more – the auxiliary can be way more than just power to get the yacht out of a marina. The 29 opens up the possibilities of motor sailing, especially as it can handle heeling up to 25 degrees without suffering lubricating oil starvation and has the torque to push the yacht against tide races or maintain control over bars.
Having been a yachtie since my teens (a long time ago now) I firmly believe that a powerful auxiliary really makes a cruising yacht. And this 29 would offer a complete transformation without affecting fore and aft hull trim.
THE NITTY GRITTY
Like all Sole marine diesels up to the silky smooth straight-six SM 105, the 29 is marinised in Barcelona from a Mitsubishi tractor engine base. It’s all cast iron, with a gear-driven camshaft operating overhead valves via pushrods, so it’s virtually bulletproof. Longevity is enhanced by the oversquare bore/stroke dimensions that reduce piston speeds. Heat exchanger cooling is standard, and with indirect injection and efficient air/fuel combustion the 29 meets most Euro and US exhaust emission regulations.
The one drawback of using a tractor base is having no provision for hand starting. However, with a 22:1 compression ratio and no de-compression levers this would be virtually impossible anyway.
The voltage-regulated alternator pumps out up to 40amps, so providing a starter battery is fitted in addition to the house battery and all electrical connections to the 1.2kW starter motor are kept clean, this shouldn’t be an issue.
The starter motor is mounted well above the engine bearers, while the alternator – driven by a V-belt that also runs the freshwater circulating pump – is mounted high and just forward of the heat exchanger.
The sump oil dipstick is located on the starboard side, just ahead of the canister oil filter that’s mounted on its side to reduce the risk of oil dribbles down the cylinder block when replacing it. The gearbox has a separate dipstick that – like the sump dipstick and oil and heat exchanger filler caps – is bright yellow to contrast the dark blue of the engine. Very nautical!
Sole doesn’t mention suitable lubricating oil viscosities in its engine literature so I’d suggest using diesel-specific SAE 10W30 oil in colder climates and an SAE 15W40 in tropical conditions. If the engine is used frequently the oil and filter should be changed every 200 running hours or annually; if infrequently, every 100 hours or six months. From information supplied by Mitsubishi industrial engine agents I suggest warming a cold engine for five minutes before applying load but no more than 10 minutes to prevent cylinder bore glazing that would result in power loss and higher oil consumption down the track. A sump extraction pump is standard.
For the additional torque and power compared with the Mini-17, the 29 is only slightly bulkier. Its 650mm length is only 35mm more than the 17, while at 446mm there’s only a 10mm width increase. However, 532mm tall is a 29mm increase, though overall still comparable with the old 12hp single likely to have been originally fitted to a yacht like a Clansman 30. The engine bearers will have to be lengthened but even so the 29 shouldn’t adversely encroach on cabin space.
Sole offers a choice of Italian-made Twin Disc/Technodrive or Japanese Kanzaki mechanical gearboxes. The latter has a seven-degree down angle at the gearbox output flange and this may create installation issues as the old engine bearers would have likely been designed for straight-output flanges. The box also adds 4.0kg to the overall weight. The standard TMC-40 ’box has ratios of 1.96:1 to 2.61:1 – the higher ratio may enable an existing prop to be used, though the prop shaft may need enlarging to cope with the additional engine torque.
Sole offers a standard instrument panel including analogue tachometer, temperature gauge with digital engine hours and the usual low oil pressure and high coolant temperature warning lights/alarms; it measures 200 x 150mm. The deluxe panel gains a voltmeter and oil pressure gauge but measures 250 x 150mm, perhaps a bit large for the cockpit of a relatively small cruising yacht.
THE WRAP
Vibration transmitted through a hull may massage the flab away but on long voyages under power or motor-sailing it’s tiring and for peace of mind less vibration is better. What’s the point in investing in a classic yacht if the engine is going to shake it apart?
The Mini-29 provides a good blend of torque and power in a compact package that can only value-add to a classic cruising yacht. And it’s well priced compared to the competition.
SEA TRIALS
750rpm produced 33nm of torque, 3.0bhp absorbed by prop for a fuel burn of 0.2L/hr
2000rpm produced 53nm of torque, 8.7bhp absorbed by prop for a fuel burn of 0.9L/hr
3600rpm produced 47nm of torque, 26.8bhp absorbed by prop for a fuel burn of 4.7L/hr
Note the rapid torque rise from idle and how much torque is still available at maximum output. Because this engine has mechanical injection I recommend not running it continuously below 1500rpm or above 3000rpm.
Quick specs
Engine type Three-cylinder indirect injection diesel
Rated BHP/MHP* 26.8/27.2 at 3600rpm
Max. torque (Nm) 53 at 2000-2500rpm
Piston displacement 952cc
Bore x stroke 76 x 70mm
Weight (dry w/gearbox) 105kg
*Brake horsepower/metric horsepower or PS