Rebuilding marine diesel engines

Yanmar's T-series are a good example. Discontinued a couple of years ago after a 50-year run, these relatively slow-running (1800-2200 revs) naturally-aspirated and raw-water cooled diesels developed 20-25hp in twin-cylinder form, 35-38hp in three-cylinder form and around 45hp with four cylinders.

The engines had traditional engineering features, such as large diameter bearings and wet cylinder liners, which eliminated the need to re-bore the cylinders. In fact, so reliable was this series that my local Yanmar dealer, Minards Marine, recently told me it was not uncommon for it to rebuild commercial fishing motors from Tonga and other Pacific Island nations that had been handed down from father to son, etc.

Some of these motors had survived 20 years of constant use and with regular maintenance could survive another 20 years.

But providing the cooling water passage zinc anodes have been replaced when needed and oil and filter changes performed at recommended intervals, there's no reason why modern engines with their integral dry cylinder liners can't be rebuilt. For example, even the smallest Yanmars can be bored 0.25 and 0.5mm oversize without affecting the integrity of the cylinder wall.

When I interviewed various engine reconditioning companies as to which brands of diesels were the cheapest to rebuild, the consensus was US. Although non-genuine or aftermarket parts could be used in some brands of Japanese diesels (such as Hino and Toyota industrial units which can make very good marine engines when keel-cooled and running dry exhausts), other manufacturers specified only genuine parts.

According to some of the reconditioners this made the engines almost as expensive to rebuild as to buy new and these brands included Kubota and Yanmar. Kubotas are used as base engines in brands such as Nannidiesel, but Yanmar markets its own motors - so I asked Con Mammides of Power Equipment (Aussie distributor for Yanmar) why this was so.

According to Con, Yanmar parts are made by wholly-owned subsidiaries of Yanmar itself, not companies contracted to make components. Con said that Yanmar spare parts are no more expensive than any other manufacturer and that the spare parts needed in rebuilding a diesel fall into three categories.

The cheapest are 'pirate' parts, those appearing like the genuine component but made of substandard materials. Next cheapest are 'genuine rejects', where parts which fail to make a manufacturer's quality control standards are rejected and bought up by some reconditioning companies. These parts appear genuine but are really no better than the pirate parts, and apparently one US diesel manufacturer has recently created immense dissatisfaction among owners of its diesels by unfortunately including some of these parts in overhaul kits.

But the fact remains that reconditioning parts for diesels designed specifically for marine usage are more expensive than diesels also used in road transport. According to Detroit Diesel Allison, incredibly only about one in 10,000 of its diesels ends up in a marine application, so that if a manufacturer's larger diesel range is not used in road transport the economies of scale dictate the parts will be more expensive. Add the fact that with the fluctuating yen spare parts prices are going to be more expensive than diesels imported from Europe and you begin to understand why the genuine Yanmar reconditioning parts cost what they do!

Boat-owners should remember that with the marginal retail price mark-up on marine diesels over 'cost price' the distributors must make their money somehow and sales of spares helps make the engine distribution business viable. It's the same in the automotive industry, so why shouldn't the marine engine distributors make a decent living?

Graeme Avers of Eastern Engine (Aussie distributor of Volvo marine engines) told me that Volvo didn't become a market leader in marine diesel sales by offering substandard parts for reconditioning. All the parts were backed by a factory warranty and if boat-owners still regarded the parts as too expensive, Volvo offered an extensive range of exchange components, such as cylinder heads, turbochargers, etc, which have been checked for quality and are guaranteed.

Another option is the range of Volvo overhaul kits, which are substantially cheaper than buying individual components.

Using these kits as a guide, Graeme kindly supplied overhaul costs of three popular Volvo diesels. To overhaul a 10-year-old 20hp 2002, the cost is only 25% of new replacement cost - not bad at all for a marine-only diesel. This also applies to a 20hp 2020 up to 10 years old.

And for a 5-10 year old 200hp AD41, the overhaul cost is 27.5% of the new price - still very reasonable in my opinion.

Overhauling US diesels works out quite cheap. There are about a dozen different ways of sourcing Caterpillar diesel spares and according to Peter Teterin of Newcastle reconditioning company Teterin Engineering, a new Cat 3408 diesel costs around $40,000 to buy in bobtail form (sans gearbox). But to fully rebuild this motor using genuine new Cat Marine parts costs about $20,000, making a rebuild an excellent alternative to buying a new motor.

Regardless of the brand, the one common comment made by reconditioners and the engine manufacturers alike was that a large percentage (99.9% according to Con Mammides) of engine failure necessitating a rebuild is due to operator negligence. For example, one reconditioner told me that a perfectly good diesel was ruined by the operator ignoring an overheat warning light. The operator kept the engine working until it seized, then complained about the standard of the manufacturer's engineering!

Other factors that cause a diesel to wear out faster than it should are not changing the oil and filter at the manufacturer's recommended interval and not warming up or cooling down turbocharged engines after a long, hard run. Alternatively (and a common problem with diesel planing hulled cruisers) the turbocharged engine isn't worked hard enough, causing the cylinder bores to glaze and necessitating a re-bore.

According to Minards Marine, the worst offenders for lack of maintenance are yachties who generally leave the motor alone until it breaks down. Minards says that only one in four or five of these engines can be rebuilt due to the neglect they suffer.