It’s that time of year when the engine needs a bit of attention for, hopefully, trouble-free cruising – obviously you can get your boatyard or mobile tech to do it or you can save money and do it yourself
If you want trouble-free cruising this spring and summer, give your engine some love
If you are going to go down the DIY route on engine servicing for the first time, get hold of the engine manual because most engines have their own particular little quirks. Have a hunt online, there are plenty out there for most engines.
Not only will you know what the engine company thinks should be done and at what time interval, you’ll also get the technical information and settings you need. You will also normally find that ‘extra’ items are listed for longer service intervals and some things that good practice dictates are rarely listed.
Perhaps the most important task is the oil system, although with the risk of diesel bug some would say that the fuel system should come first – but we’ll stick with the oily bits this issue and deal with the fuel side next month.
Look in the manual to find the viscosity of the engine oil required; on modern engines it’s likely to be something like SAE 15W40 or 10W40. Older engines may use 20W50 or even SAE 30.
Also check the quality of the oil required. This is critical for inland boats because apart from how hard you use the engine, getting the quality right is about all an owner can do to avoid cylinder bore glazing. Typically you will find a range given, for example CC to CE. This means API specification C (for compression ignition engines – diesels), performance C to performance E.
For inland use with much light and no-load running use, that’s the letter closest to A (in this case CC), for estuary and offshore use choose the higher letter for better lubricating performance (CE). The correct oil may take a bit of
searching for but it’s well worth it. Some engine manufacturers market suitable oil under their own name, while smaller producers such as Morris Oils also produce it, especially for older engines.
Petrol engines follow the same scheme but the prefix letter is S (spark ignition).
If you have a separate gearbox and reduction box, check the viscosity and/or type of oil required. Modern boxes use engine oil and have a built in reduction, but older ones could use anything from engine oil or automatic transmission fluid to EP80 gear oil.
Before starting, place old rags or an oil absorbent bilge blanket in the engine tray to catch drips and spills. If any engine mounts are positioned where oil can be spilled onto them, cover them in rag or something like plastic wrap.
Run the engine to raise the oil temperature. Feel the sump and when it starts to feel hot, stop the engine and pump out the oil using whatever method is easiest. A well marinised engine will have a drain pump fitted, otherwise use a vacuum oil extractor or manual pump with a tube down the dipstick hole.
A pump fitted onto the engine should either have a ‘bung’ fitted into its outlet and/or a tap. This pump might also drain the gearbox, in which case the tap should be switchable between ENGINE, OFF and GEARBOX. If the tap is not turned off or the bung refitted after use oil might drip from the outlet whenever the engine is running.
Modern engines use a ‘spin-on’ filter that’s a throwaway unit, while older engines tend to use a throwaway element inside a metal housing. In the case of the latter look to see if it there is easy access to the bolt head that holds the bowl onto the filter head. If not it might be easier to take the whole assembly off the engine. If this is the case you will need a gasket for the filter to engine joint.
Remove and replace the oil filter and clean all the old oil away from the filter etc. Then have another go at the draining
to remove any oil that has dripped down inside the engine.
Fill the engine with fresh oil to a point anywhere between the maximum and minimum level on the dipstick, then start the engine on idle and let it tickover until the oil light goes out, checking around the filter for leaks.
Stop the engine, leave it for a short while and top the oil up to a fraction below the maximum, then run the engine at a higher speed and recheck for leaks.
Changing the oil in the gearbox and reduction box oil is very similar. If you have a PRM box it might be better to drain it via the drain plug because using an extractor via the dipstick hole on some of these boxes will not extract all the oil.
If there is any sign of a whitish tinge to the oil, the colour indicates the presence of water and requires further investigation; engine oil tends to look greyish and gearbox oil goes to a cloudy, creamy colour.
VALVE CLEARANCES (THE TAPPETS)
Check in the manual to find out whether the valve clearances are adjustable (most are, but a few are not or use oil pressure to do it automatically), whether the engine has to be hot or cold; if both valves (inlet and exhaust) are set the same or to different gaps.
On most modern engines the tappets are adjusted cold and both valves are set to the same gap – but do double check. Some older Listers, for example, used radically different gaps on the inlet and exhaust valves.
You can inspect them for wear and cracking, but in some respects it’s easier simply to replace them every two or three years and keep the old ones as spares.
The correct tension for a ‘normal’ V belt is about 1cm deflection in the centre of the longest run between the pulleys under moderate finger pressure. While over tightening is likely to strain the water pump bearings, the fashion for retro-fitting high output alternators might demand a tighter belt.
If your engine has wide poly-V belts with lots of small Vs running around the inside face of the belt it needs to be adjusted more tightly. Unless you have a belt tension gauge tighten the belt until you can twist it through just 90 degrees in the centre of its longest run.
Older filters usually have a metal housing
A well marinised engine will have an oil drain pump fitted
The dipstick and filler hole on a gearbox
Using ring spanner, screwdriver and feeler gauge to adjust the valve clearances
Checking the drive belt tension