Which standard engine came in the Arcona 340, and what common weaknesses should I check?

The Arcona 340's standard engine was the Yanmar 3YM20, advertised as 20 hp in the February 2010 specification. Check the engine and drive identification plates first, then inspect cooling, the exhaust mixing elbow, engine mounts and drive seals; these are priorities on an ageing installation, rather than evidence of a particular Arcona defect.

Confirm engine and drive

The 3YM20 is a three-cylinder, freshwater-cooled marine diesel. Its closed coolant circuit transfers heat to seawater through a heat exchanger, giving you two separate cooling circuits to inspect.

The original specification identifies the engine, but not the drive model. Record both identification plates and compare them with service invoices, as either unit may have been replaced. The later Arcona 345's published 3YM20/SD25 combination does not establish what an earlier 340 carries.

Ask for a cold start without anyone running the engine beforehand. Feel the engine before starting, check oil and coolant levels, and watch how quickly it fires. Brief smoke can occur at startup. Persistent white smoke, blue smoke once warm or heavy black smoke under load needs investigation. Engine hours help, but regular servicing and a convincing sea trial matter more than a low counter reading.

Cooling and exhaust elbow

Inspect the seawater path first. An engine can appear healthy alongside yet overheat under load. Follow the seawater path from the inlet and strainer through the raw-water pump, heat exchanger and exhaust injection point.

• Look for salt tracks, green corrosion, loose hose clips and hardened or cracked hoses.
• Check the raw-water pump for leaks and ask when its rubber impeller was changed. If an old impeller lost blades, establish whether the missing pieces were recovered downstream.
• Inspect the heat exchanger end caps and joints for leaks. A new impeller will not cure a restricted exchanger.
• Examine the exhaust mixing elbow, where seawater enters the exhaust. Internal carbon and corrosion can restrict it even when the outside looks sound.

A restricted elbow can contribute to poor power, black smoke and overheating. Removing it gives a much better assessment than an external glance. Inspect the exhaust hose and waterlock too, particularly for leaks, deterioration or signs of excessive heat.

Never remove the coolant pressure cap while hot. Keep hands, clothing and tools clear of belts and rotating machinery during running checks.

Mounts, fuel and sea trial

Check the flexible engine mounts for split rubber, corrosion, loose fasteners and oil contamination. Excessive movement when engaging gear, or vibration through a particular speed range, calls for checking the mounts, propeller and drive installation together.