Renovating sterndrives

In past instalments of Engine Talk we have discussed the viability of re-powering older cruisers, which for some local diesel distributors accounts for 50% of their sales.

For example, a popular choice among Bertram 28 owners has been to swap the existing petrol V8 inboards for twin four-cylinder turbo-intercooled Yanmar diesels, which provide comparable performance for much lower fuel costs.

But buying a sound 28 for around $50,000 then spending another $60,000 on the engines can result in over-capitalisation of the boat and the need to "run it into the ground" to recoup the outlay. So when a regular Trade-A-Boat reader, Scott Fuller, told me about his experiences when renovating the Volvo AQD40A turbo-diesel sterndrives in his Riviera 30 without resorting to engine overhauls, I was particularly interested to hear how it had been achieved.

Scott is the Managing Director of a marine website that supplies engine parts and accessories. When I talked with him last August, he was in the process of putting the Riv into survey for charter work on Sydney Harbour.

THE ENGINES
According to Scott, the existing engines had been "unloved" since 1989. As expected, the first problem was to overcome glazed cylinder bores, a common problem with turbocharged diesels that have mechanical injection and fixed timing.

Many boaters buy planing-hulled cruisers with the idea of sprinting out to their favourite anchorage. They opt for diesel engines to save fuel, reduce insurance costs and eliminate the perceived explosion risk of petrol inboards, which in reality are safer than most gas stove installations.

Unfortunately, most cruiser owners find their diesels are too thirsty to run for extended periods at planing speeds and tend to cruise at displacement speeds with the engines at fast idle, below where the turbochargers start to come on boost.

Running any straight turbo or turbo-intercooled diesel this way for extended periods creates no end of problems, such as rapid combustion chamber carboning-up and cylinder bore glazing.

Because mechanically controlled diesels have fixed injection spray timing, which is normally designed for maximum effectiveness in the middle of the engine's torque band, at low speeds the fuel is sprayed too early into the combustion chambers. It's like running a petrol engine with the choke valve left partially closed. Not only does the excess fuel dilute the film of lubricating oil left on the cylinder walls, but it also produces excessive carbon, particularly in indirect-injection diesels.

Normally, the only way to overcome cylinder wall glazing is to re-hone the bores to retain the film of oil needed to reduce metal-to-metal contact. However, Scott overcame the glazing by using a Nulon PTFE (Teflon) additive in the engine oil.

To improve engine performance by reducing exhaust back pressure, Scott cleaned out the exhaust elbows, which were full of gunk from excessive carboning-up of the cylinders. The oil coolers were acid rinsed and all aluminium components sandblasted back to the original finish. All oil seals were checked and replaced where needed.

THE FUEL SYSTEM
Scott used a combination of Algae X magnetic fuel conditioner and Algae X fuel catalyst to treat the fuel system.

The conditioner is installed in the fuel line and, according to Scott, works by passing the fuel through a magnetic flux to improve the chemical stability and combustibility of the fuel. Apparently, the device can also reduce the degradation of oils and hydraulic fluid. It comes in a range of sizes from 75mm wide, 75mm deep and 30mm high to 178 x 178 x 330mm, depending on the fuel flow.

The catalyst is added to the fuel tank and contains a combustion catalyst, surfactant, dispersant, corrosion inhibitor and lubricity enhancer to restore contaminated fuel back to straight diesel. It assists the inductive effects of the conditioner to remove combustion chamber carbon deposits, which in turn improves engine fuel efficiency.

Using these two systems, Scott was able to clean the Volvos' injectors without having to remove them, saving a significant amount of time and cost. And according to Scott, no black exhaust smoke occurs and the transom is now clean.

THE COOLING SYSTEM
To put the Riv into survey, the existing cooling water intakes through the sterndrive legs had to be bypassed and a separate through-hull intake with seacock fitted for each engine. The existing plastic water hoses were replaced with reinforced rubber hoses.

Waterpump impellers in both the seawater and heat exchanger systems were replaced after acid rinsing the heat exchangers and flushing the freshwater circuit three times with coolant.

THE LEGS
Drive legs are normally the bane of older sterndrive cruisers left on moorings and can cost a fortune to rebuild. This is why all current-model Riviera cruisers have shaftdrives.

But on Scott's Riv, the Volvo 280 units were in good condition and required very little work to put them back into running order.

All that was needed was to replace all the oil seals in the gearbox housing and lower units (a job he did himself without too much effort) and fit new zinc anodes and universal joints. Apparently, there was no need to renew the rubber diaphragms between the legs and transom.

CONTROLS, INSTRUMENTATION AND ELECTRICAL
For the upper and lower helmstations, the Riv had twin lever (heaven help the charter skipper!) Morse Teleflex throttle and gear controls, which were disconnected and internally oiled for hassle-free operation.

Scott installed a second set of VDO instrumentation on the flybridge to duplicate the lower helm and fitted dual senders on the engines as a back-up against failure.

The engine alternators were still serviceable, but the battery cables, earthing straps and battery retain straps were replaced. Two starter batteries and one deep cycle unit were installed with the house battery being charged by the starboard engine.

A NEW OPERATING PROCEDURE
Although the Riv will be operated mainly at displacement speeds while on charter, Scott says the skipper will be instructed to operate the boat at planing speeds for at least 15 minutes prior to the end of each charter.

This procedure should overcome any glazing problems and will also help burnish the antifouling for a longer lifespan between re-coats.

For more details on Scott's Riv 30 renovation, contact him on (02) 9223 3199 or visit his website, www.marinedirect.com.au for information on the Algae X conditioner and catalyst.