ENGINE REVIEW - NANNI DIESEL N1.7

Way back in the early eighties Western Fuel Pump and Injector Services, at the time a distributor for Yanmar marine diesel engines, also imported a little petrol inboard from Finland.

Made by the industrial conglomerate Valmet and known as the Vire 7, this single-cylinder two-stroke engine was fitted to yachts such as Sonata 8, S80, Folkboat, Vandestaat 24 and J24 keelboats.

Trouble was, whereas the Pup had a removable magneto to prevent dampness affecting the ignition system during periods of disuse, the Vire 7 had a magneto located in the flywheel that not only was affected by dampness but a pain when it came to servicing the breaker points. I had seriously considered fitting one to my 6.7m Bluebird keeler but owner reliability reports soon axed that idea. I could just imagine bilge water in the plywood hull corroding out the points, and at the time retailing for $1700 excluding stern gear, it made outboard auxiliaries look very attractive!

The Vire 7 has long gone but what can owners fit should their investment need a repower? One answer is the Nanni Diesel N1.7, a watercooled industrial marine engine.

Nanni Diesel N1.7

The N1.7 is the only small Nanni Diesel not having a Kubota base. The base engine is made by German lifeboat-engine specialist Farymann and has direct injection with automatic decompression for hand starting. Unusually, although the cylinder head and block are cast iron the crankcase is aluminium. Other quirks are a flywheel-mounted alternator that pumps out a puny 13amp and a starter motor mounted aft of the flywheel. The seawater pump for the thermostatically-controlled cooling system appears to be driven by the camshaft that operates pushrods for the overhead valve arrangement. There are no belt drives on this engine.

Unfortunately Farymann doesn’t fit a raised hand-crank system that free wheels when the engine fires up. A simple hand-crank is fitted to the crankshaft and the engine spun. If it flips back during cranking a broken wrist awaits. This is one reason why Henry Ford fitted an electric starter to his Model T. Farymann really should have looked at the raised crank design of the old Lister lifeboat diesels, especially as the compression ratio is a relatively high 20:1 compared to around 16:1 for the Listers.

One reason why the CR is so high for a direct injection engine is the big-bore/short-stroke design. Longer stroke engines can get away with lower CRs, but this is not a bad thing. Regular visitors here know how I’ve knocked single-cylinder diesels for boats, because of the high vibration compared to twins. However, recent engine reviews I’ve done on a range of single-cylinder engines, petrol and diesel, have shown that the less the piston travels in relation to cylinder bore width, the less vibration occurs.

The Nanni Diesel N1.7’s piston stroke is only 67 per cent of the bore dimension, in line with a lot of industrial diesels, petrol engines from Briggs & Stratton and even small four-stroke outboards such as Mercury’s F2.5 which has a stroke of only 65 per cent and transmits virtually no vibration through a hull. So unlike the more traditional single-cylinder diesels where bore and stroke dimensions are the same or the stroke is longer and which try to shake your teeth out (God help those with dentures), this shouldn't happen with the N1.7.

The oil sump capacity isn’t bad either. At 1.2lt it’s big enough to absorb oil dilution that occurs from piston ring blow-by between oil changes, though I still recommend changing the oil and side-mounted canister oil filter every six months or 100 hours of operation as the N1/7 runs cold compared to a heat exchanger-cooled diesel. The deep sump allows for a maximum continuous hull heeling of 27 degrees, so a yacht can be effectively motorsailed without fear of oil starvation. Nanni Diesel doesn’t mention the type of oil required but I recommend either diesel-specific SAE 30 or SAE 15W40 oils.

The Vire 7 measured 480mm long, 450mm wide and 405mm high, whereas the N1.7 is 578 x 428 x 413mm, so apart from a little extra length encroaching on accommodation space the width and height won’t create too many issues. The Vire dimensions included a muffler, while the Nanni Diesel N1.7 needs an external unit.

The ZF10 mechanical gearbox is available with ratios from 2.1:1 to 2.7:1 and choosing the right one will depend on the maximum size of prop that can be fitted. But whichever ratio is chosen, the prop can free wheel if a folding prop is not fitted as the box doesn’t need engine-driven lubrication.

The Trade-a-Boat verdict

The Nanni Diesel N1.7 marine diesel engine can be used in small keelboats that simply can’t handle the weight of even a twin-cylinder diesel, yachts such as the ones mentioned and the old Endeavour 24 and 26. It’s a way safer proposition than a carburetted petrol inboard such as Simplex 5 and in any case Aussie yachties prefer diesel inboards, so resale value will be higher too. It also suits inboard launches to 5.5m. The hand-starting facility is great, but please Nanni Diesel fit raised hand cranking!

More information: nannidiesel.com.au

Nanni Diesel N1.7 performance

For such a small engine the Nanni Diesel N1.7 has good torque output and an almost flat torque curve. As it has fixed fuel injection timing I recommend not running it continuously below 2000rpm or above 3000rpm.

* Sea-trial data supplied by the author.

Nanni Diesel N1.7 specs

TYPE Single-cylinder direct injection marine diesel engine

RATED BHP/MHP* 7.0/7.1 at 3600rpm

MAX TORQUE 15.3Nm at 2500rpm

DISPLACEMENT 290cc

BORE X STROKE 82 x 55mm

WEIGHT 64kg (dry, w/ gearbox)

* Brake horsepower/metric horsepower or PS