BETA JD3 DIESEL ENGINE REVIEW

Back in the 1950s pleasureboat diesel engine were considered high-revving if they reached 1800rpm. British diesel engines such as the twin cylinder Ailsa Craig developed 20bhp at only 1200rpm, while the Thornycroft ‘Handybilly’ RJD2 developed 12.5 to 16bhp at 1500 to 1800rpm.

Unlike the current mhp (or metric horsepower) favoured by European and Japanese engine manufacturers, which equals 735.5 Watts per horsepower, bhp is the traditional 746 Watts per horsepower and a true indication of what an engine can develop.

Don’t be fooled by the low outputs of the old hand-start Ailsa Craig and Thornycroft engines. These produced torque figures closer to what a 30 to 40bhp diesel develops than their stated outputs. The only drawback was their massive weight relative to output, but then an engine should always be judged on its torque output rather than maximum power.

UK-based Beta Marine has long been manufacturing a range of naturally-aspirated Beta diesel engines, based on Kubota and Iveco engines. These normally develop maximum power from 2600 to 3600rpm depending on the output and are all freshwater (heat exchanger) cooled with conventional fuel injection systems of no more than 140bar (2000psi).

But the Beta JD3 diesel engine is a throwback to the days when torque was way more important than maximum bhp, something that a nerd like me can really appreciate!

BETA DIESEL ENGINES

Based on a three-cylinder 2.9lt John Deere pushrod ohv crossflow engine, the JD3 develops a mere 35bhp (Beta rates all its engines this way) at 1400rpm and is designed to operate over a range of 450 to 1200rpm. Best of all is the torque, a massive 180Nm at 1200rpm.

To put this in perspective, the Kubota-based four-cylinder 2.4lt Beta 60 develops 56bhp at 2700rpm and 172Nm at 1800rpm. Complete with mechanical reduction gearbox the dry weight is 287kg, whereas with a PRM hydraulic box the JD3 is a hefty 490kg, substantially more than the 3.8lt Beta 90 weighs.

So why would a boat owner choose a JD3 over a higher-revving diesel that not only develops way more power but is a lot lighter?

For a start, with its massive flywheel the JD3 produces useful power and torque from only 450rpm, whereas the Beta 60 will idle down to no less than 800rpm. This means that with the standard 1.96:1 reduction, the JD3 has plenty of grunt down low, perfect for towing duties in a yacht club rescue boat.

And even at the maximum continuous rpm of 1200 the noise levels are way lower than the Beta 60 cruising at 2500rpm. In addition to the dynamically balanced crankshaft, the JD3 has a two-stage damper system that is designed to eliminate low-speed gear chatter. An indication of its balance is that the engine has a solid mounting system unlike the individual feet of higher-revving engines.

The JD3 is set up for keel cooling with a dry exhaust stack next to the rocker cover. Keel cooling is perfect for boats that regularly operate in shallow water. And with its engine and gearbox oil coolers, the JD3 is never likely to overheat.

There’s a cyclonic air cleaner and the mechanical fuel lift pump has the traditional hand primer. The voltage regulated alternator produces up to 70amp with provision for mounting a second 100amp unit or a 3.5kVa 230V alternator for domestic fridges etc.

A tachometer and engine running hours meter are included in the standard instrument panel but frankly I’d be ticked off having a tacho showing up to 4000rpm when the engine can reach only 1400. Surely Beta could tailor a specific tacho for this engine!

Back to tradition. There’s a brass oil pressure gauge on the side of the engine, while the rocker cover is a mix of polished copper and gunmetal, complementing the standard green paint – way nicer than than the red of the Kubota-based range.

Like all of the Beta diesel motor range the starter motor and alternator are mounted well above the engine bearers, though the angled-down oil filter will dump oil everywhere when replaced. I’d change the engine oil and filter every 200 hours or annually after the first 20 and use either SAE30 or SAE15W40 oil. The standard hand pump will make draining the sump way easier.

THE VERDICT

The JD3 is a dedicated towboat engine and better suited to yacht club duties than powering a displacement cruiser. Its massive weight dictates that it be mounted in a pure displacement hull up to around eight-metres. Propping would be fun as with maximum prop rpm of 714 a specially-designed coarse-pitch prop is the only way the engine torque can be converted to thrust, so a four-blader may be needed to gain sufficient blade area and reduce prop diameter.

Knowing an engine like the JD3 is still available makes an old fart like me very happy, raised in a era when small marine diesels rarely exceeded 2000rpm.

For more on the JD3 contact Graham at Beta Diesel Australia, phone (02) 9525 1878 or email: sales@betadiesel.com.au

BETA JD3 DIESEL ENGINE PERFORMANCE

The Beta JD3 diesel has torque and bhp figures unlike any other 35bhp diesel currently on the Australian market.

BETA MARINE JD3 DIESEL ENGINE SPECIFICATIONS

TYPE Three-cylinder diesel

RATED HP 35 at 1400rpm

TORQUE 180Nm at 1200rpm

DISPLACEMENT 2900cc

BORE x STROKE N/A

DRY WEIGHT 490kg (with gearbox)