Running in Inboards

It could be argued that the first hours of an engine's life are its most important. Only by running in (or breaking in) a new powerplant correctly will you ensure that it performs at its best, avoiding potential problems such as glazed cylinder bores down the track.

There are a number of theories on running in. Some boaties subscribe to the flat out from day one routine, others insist on babying new powerplants. In their own way both approaches are wrong.

So how do you run in a marine powerplant?

This depends on the type and size of the powerplant in question diesel and petrol powerplants require differing procedures.

Following are some pointers, but I'll begin with a quick word on oils...

Whether you run a petrol or diesel inboard, it's imperative that you do not use friction-modified oils during the run-in period. No ifs, no buts...

Indeed, once you've settled on a specific oil for the break-in period, it's a good idea not to change the type or brand of oil at the first service, either. Put simply, oils ain't oils and all have slightly different chemical compositions that can create different bearing and piston ring wear in your motor.

SPARK IT UP
The running in of petrol engines is, in reality, a simple process with some easily drawn parallels across a range of powerplant size and types. Hylton Hamilton of Hamilton's Marine in Newcastle (NSW) sells MerCruisers and his years of experience in the marine industry have given him a thorough knowledge of how engines should be broken in.

Hamilton recommends avoiding Wide Open Throttle (WOT) and extended low speed operation with new MerCruiser inboards and sterndrives for the first 10 hours.

Motors should be warmed up in gear at low revs for a few minutes before opening up and similarly cooled down in gear for a few more before switching off. Ensure that you vary throttle openings during the initial 10 hour period.

These are sound practices that can be applied to almost all four-stroke petrol engines and are close to those recommended by most manufacturers.

Of course, if you have any doubt you should check with your dealer and/or engine supplier. Hamilton suggests using a heavy duty SAE 15W40 oil (never an automotive 20W50 oil). Like the writer, he favours Valvoline oil in his petrol four-stroke motors.

After the first 20 hours the oil and oil filter should be changed. Hamilton emphasises that you shouldn't swap brands of oil once you've broken in your motor on a particular brand.

OILERS AIN'T OILERS
Despite their seemingly robust nature, diesels can easily be damaged if the following aspects are not considered. First, will the propeller fitted allow the motor to reach its recommended WOT rev range?

There are few things worse than an overpropping to reduce diesel engine life. If the motor blows black smoke anywhere across its rev range, it is a good indication that a prop with too big a pitch is fitted and the engine overloaded. In theory diesels should produce only a heat haze from their exhausts (those with dry exhausts) or water only for those with wet exhausts.

If your boat has a planing hull and a good power to weight ratio, slight overpropping will not be too detrimental, providing that no black smoke appears during the transition from displacement to planing speeds.

This is where modern design powerplants like Volvo's Kompressor series and Yanmar's 6LPs score because the forced induction systems are designed to supply boost from very low in the rev range (the Volvo system via a combination of super and turbocharging). However, if you have a single-cylinder 10 hp diesel in your 9.0 metre yacht, it must rev right out to its designed WOT rev range.

For example, small Yanmar diesels are designed to reach 3600rpm, so for yacht auxiliary usage they should be slightly underpropped to reach about 3700rpm in calm water. This will allow for headwinds and strong tidal currents which rapidly load up a small engine.

Secondly, how frequently will the motor be used and under what load conditions?

According to Richard Minard, who for years has sold both recreational and commercial Yanmar diesels throughout the Hunter (NSW) region and more recently to other parts of the world, the break-in period will vary according to how frequently the motor is used and how it is loaded.

For example, with frequently used motors about 20 hours of break-in will suffice. In the above example, the motor should be idled for only a few minutes then slipped into gear and run at about 1800-2000rpm for at least five minutes to fully distribute lubricating oil. Never run the motor for very short periods such as motoring out from a mooring to raise the sails until it is fully run in.

Once fully warmed (five minutes for naturally aspirated motors, 10 for turbos) the motor can be gradually opened out to within about 200 revs of WOT for short periods of time, returning to 3000rpm or less for a cooling period. This will ensure the bearings and piston rings bed in correctly.

After a long run, cool down the engine at 2000 revs in gear for about five minutes, then idle it for less than a minute before switching off. Turbocharged diesels should be cooled down for at least 10 minutes.

Finally, choose a good quality oil and stick with it. Minard recommends 15W40 Shell Rimula X (a heavy duty truck oil) or Shell Nautilus diesel oil, which essentially is Rimula X with corrosion inhibitors added. And he advises against using low viscosity 'break-in' oils that are sold by some oil companies for four-stroke engines.

According to Hylton Hamilton, who also sells diesel Volvo and Mercruiser inboards and sterndrives, diesels must be kept at least 200 revs below WOT for the first eight hours. He believes that Volvo's running recommendations to operate the powerplant normally but avoid full load during the first 10 hours of operation are a good guide to follow no matter what the brand of engine.

After the initial period recreational-rated motors should not be operated at WOT for more than one hour in any 12. For light duty commercial rated motors (such as those in charterboats), he suggests an eight hour period of run in, followed by no more than two hours of WOT in any 12.

When not operated at WOT the engine must be run at no more than 90% of maximum output. And like Minard, Hamilton says no diesel likes idling for extended periods, even when run in. If used this way any diesel, even a naturally aspirated unit, can suffer glazed bores.

The bottom line is that when you're in doubt about the correct break-in procedure for your petrol or diesel engine, you should contact your dealer or engine supplier.

And our top tips? Take your engine supplier's advice especially regarding first and regular service intervals and above all use your commonsense. If you have not already done so, fit an accurate hour meter. That way you'll know when it's time to change the oil and filter and open her up.

Modern marine powerplants are not inexpensive and guesstimating service intervals, even your running-in period, is far from wise.