Cummins N14-M

Developed from the proven NTA855-M inline six diesel, which first appeared in 1964, the new Cummins N14-M suits workboats to around 16 metres and, in twin installations, cruisers and gameboats from 12-14 metres.

A 14lt turbocharged aftercooled diesel, the N14-M is available in five output ratings and three duty cycles from 360 to 525 hp. Maximum torque is developed in the usefully-low 1400-1500rpm range and the motor is somewhat more compact than its predecessor.

A direct injection motor with 17:1 compression ratio, the N14-M features 'step timing control', which hydraulically alters injection timing for the optimum fuel spray pattern at any given revs. As most owners of diesels know, fixed injection timing is very much a 'hit or miss' situation as the timing is set up for the peak torque range. Above or below these revs the timing is either too retarded or too advanced, creating unburnt fuel problems which appear as white smoke. In this age of rapidly-tightening emission controls, fixed timing is just not acceptable for a large marine diesel.

Apart from the utilisation of STC fuel-injection, the N14-M's turbocharger and injectors have been completely redesigned.

Changes to the engine itself include the new cylinder block and head, cylinder liners, pistons, rings and connecting rods, crankshaft, camshaft and valve guides.

Even the air filter has an inlet restriction indicator. Based on my past experience as a charterboat skipper, a clogged air filter can reduce engine output when you least expect it.

In line with the raised output ratings, the Holset turbocharger has been enlarged and the oil cooler capacity increased and fitted with an integral corrosion resistor. This is externally mounted for ease of field servicing. The lube oil sump holds 57lt to reduce the effects of sludging between oil changes, but I would prefer a cast iron sump instead of the cast aluminium unit. O-ring seals in the cupro-nickel heat exchanger core reduce the need for hoses with clamps and the N14-M is suitable for either heat exchanger or keel cooling (the latter system running a dry exhaust).

The N14-M's cylinder block is now ribbed to reduce transmitted noise and has straight-thread O-ring connectors to reduce possible fluid leakages.

The redesign has seen a move to larger crankshaft and conrod bearings. This has created 25% more bearing surface area good news for high-usage operators.

Micro-finishing on the injector lobes and camshaft followers reduce friction and subsequent component wear.

An alloy cast iron cylinder head with larger exhaust porting is fitted to the N14-M and there are now stellite-faced valves, rotators and cast iron valve guides. According to Cummins, these changes result in better throttle response and fuel efficiency, plus lower exhaust emissions via the use of a ceramic-clad manifold which allows for easier gas flow to the turbocharger.

The N14-M's rocker housing is cast iron with more coolant ports, thus eliminating the need for an external water manifold, Cummins says.

The wet cylinder liners have a new surface finish for better resistance to piston ring scuffing, while the new articulated pistons have alloy steel tops and a revised combustion dish inserted in aluminium skirts. The piston rings have also been relocated further up the piston walls to reduce emissions, but in the long run this could increase the possibility of piston slap.

Larger conrod struts and big end and wrist pin loops complete the makeover in this area.

All internal gears have been made wider with more surface-to surface contact for increased lifespan.

A range of gearboxes are available to suit the N14-M in all duty applications. The Twin Disc models range from 0.93:1 to 6.48:1 while the ZF units offer a range from 1:1 to 6:1. Both gearbox manufacturers can assist with selecting the right ratio box for your boat and application.

Like most diesels in this power range the electrical system is 24 volts and a 60amp belt-driven alternator is standard. Separate alarm panels for low oil pressure and high water temperature are provided for both the engine room and wheelhouse.

Though I've not yet had the opportunity to try this diesel I must confess I like Cummins' approach to engineering. The STC injection allows the N14-M to run much cleaner than a diesel with fixed timing, but is inherently more reliable than electronic engine management systems. I've spoken to many truckies who operate their vehicles under heavy-duty applications such as hauling coal, and most prefer diesels with mechanical injection systems. In highway applications at least, while the fuel efficiency initially appears attractive, the downtime that can result when computerised systems fail can outweigh the fuel savings.

Having experienced how easily marine computer-controlled management systems can fail, I would personally prefer to run a diesel fitted with STC!

Cummins is the world's largest independent manufacturer of diesels over 200 hp and its products have a proven reputation for reliability. Its subsidiary, Cummins Marine, designs and manufactures the marinised versions and provides worldwide aftersales service. To contact its Australian division, tel (03) 9765 3222.