The jobs — With your hands
Reading notes · The diesel engine
Eleven jobs, done with your hands: the oil and its filter, both fuel filters, bleeding her, the strainer, the impeller, the belt, the stern gland, a battery that will not turn her over, and starting her by hand.
Open the interactive chapter →The same material with the chart, the drawings and the exercises.
The jobs · Clean the raw-water strainer
The basket in that clear bowl is the only thing between the sea and your impeller. It fills with weed, and it fills fastest on the days you are working hardest.
Close the seacock. That bowl is below the waterline and there is an open valve under it. Take the lid off with the sea connected and the sea comes up into the boat — and the valve you need is now underneath it.
Undo the lid. A knurled ring on most, a clamp on some. It will be full of water: have somewhere for it to go.
Lift the basket out. Straight up, and look at what is in it before you empty it — weed says one thing, a shredded plastic bag says another, and black rubber crumbs say your impeller has already failed.
Empty it and rinse it. Overboard or in a bucket, not into the bilge. Check the mesh for splits while it is in your hand.
Basket back, lid on, and OPEN THE SEACOCK. Then start her and look over the stern for water within half a minute. An engine started with the seacock shut is an engine whose pump is running dry, and that is seconds, not minutes.
The jobs · Change the raw-water impeller
The first spare on everybody's list, and a lump of rubber. It is cooled and lubricated by the water it pumps and by nothing else, so it fails from running dry — and when it fails, the pieces go somewhere.
Close the seacock. Same reason as the strainer, and the same consequence if you forget to open it afterwards.
Undo the cover screws. Usually six, and they are small: a bowl or a rag under the pump before you start, because one in the bilge is one you are not going to find.
Pull the old impeller out. Two screwdrivers levering gently on opposite sides, or a proper extractor. It will be stiff and it will come.
Count the vanes. Count what came out against what should be there — the new one in your hand tells you the number. Two are missing.
So go and find them. They went downstream with the water, and the first thing narrow enough to stop them is the tube bundle in the heat exchanger. Until they are out of it, the job is not finished and she will still overheat with a brand-new impeller in her.
New impeller in, cover on, seacock OPEN. Smear the new one with washing-up liquid or glycerine — never grease, which attacks the rubber — and turn it the right way as it goes in. Then start her and look astern.
The jobs · Take the impeller out before you crank
She will not start and you are about to spend a while finding out why. Every turn of the starter turns the seawater pump — it does not know whether the engine has fired — and every turn puts more sea into an exhaust with no gas to blow it out. It collects in the waterlock at the low point, and when that drum fills it backs up to the mixing elbow and runs down towards an exhaust valve standing open. Water does not compress.
Close the seacock. That alone stops any more sea coming in, and on most boats it is all you need for a few more attempts.
If you are going to crank for long, take the impeller out. Cover off, impeller out, and now the pump cannot move anything even if the seacock is opened by somebody helpful.
Tie a note to the ignition key. «NO IMPELLER». You have just made it possible to start the engine with nothing cooling it, and an impeller run dry is finished in seconds — you swapped one way of wrecking her for another, and the note is what closes it.
The jobs · Check the stern gland
A turning steel bar through a hole in the bottom of the boat, and a box of greased packing squeezed around it. This is the check, and it is one you do with the engine running and again with it stopped.
Look at it stopped, before you go anywhere. A packed gland at rest should be still — a drip now and then is fine, a steady run is not. Dry crusty salt around it says it has been leaking and drying for a while.
Now with the shaft turning: it should drip. A few drops a minute, and that is not a fault — it is the cooling and the lubrication. Those drops are the only thing carrying heat out of packing being rubbed at cruising revs.
Feel it after a run. Warm is right. Too hot to keep your hand on is too tight, and a gland that has been run hot has hardened packing that will score the shaft — a five-pound job turned into a haul-out.
And this is what too loose looks like. A run rather than a drip, filling the bilge slowly all passage. It needs the nut nipping down a flat at a time, running her between each, until it drips again — not until it stops.
Leave it dripping, and turn the greaser down a couple of turns. That is the state you want to walk away from: a few drops a minute with the shaft turning, and nothing at rest.
The jobs · Check the engine oil
The dipstick is the only window into the whole lubrication circuit, and it is a stick. It has two marks on it and both of them are limits — and it is read cold, before you start, with the boat sitting level.
Pull it out. Cold engine, boat level. Oil that has been running is up in the galleries and not in the tray, so a stick read after a passage reads low and sends you looking for a leak that is not there.
Wipe it clean. The first reading is worthless: oil has run down the stick and smeared it. This is the step people skip, and skipping it is how a full engine reads over the top mark.
Push it all the way home, and pull it out again. All the way — a stick that stops on its seal reads short. That is the reading.
Read it between the marks, and put it back. Between, not at the top: too much oil is as bad as too little, because the crankshaft whips it into foam and a pump cannot pump foam. And the gearbox has its own stick, its own oil and its own rules — that one is a different job.
The jobs · Change the oil and its filter
Most marine engines have no drain plug you can reach, so the oil comes out the way the stick goes in. Run her until she is warm first — warm oil is thin oil and it all comes out, where cold oil leaves a third of itself on the walls. Warm, not hot: you are about to have it running down your arm.
Pump the old oil out through the dipstick tube. A hand pump or a drill pump down the tube. Get it all — what you leave behind is the dirtiest of it, sitting in the bottom.
Unscrew the old filter. It will be full and it will run down your arm. A bag or a tray under it first, and a filter wrench if it will not start by hand.
Check the old sealing ring came off with it. Look at the engine face. If the old rubber ring is still stuck there and you screw a new filter onto it, you have two seals where there should be one — and it will pump the sump out through the gap the first time you start her.
Smear the new ring with clean oil and fit it by hand. Screw it on until the ring touches the face, and then however much further the side of the can tells you — it differs between makes. By hand, whatever it says: a wrench belongs on the old one, not on the new one.
Fill through the filler cap, and stop short. A little less than the book says, because the new filter is empty and will take some.
Run her thirty seconds, stop, and wait a minute. That fills the filter and lets it drain back. And look underneath while she runs: a filter that is going to leak leaks now.
Now read the stick and top up to between the marks. This is the reading that counts — the one after the filter has taken its share.
The jobs · Change the fuel filters
Two filters, and they are not the same job. The first is the pre-filter with the clear bowl — it catches water and the big dirt, and you can see into it. The second is the fine filter on the engine, and it is the last thing between your tank and an injection pump built to a thousandth of a millimetre.
Close the valve at the tank. Everything downstream is now a closed system with a bowl you are about to open, and diesel finds its way to the bilge faster than you can find a tray.
Open the pre-filter bowl and take the element out. Look at what comes out with it: water sits under the diesel in the bottom of that bowl, and a black slime on the element is diesel bug rather than dirt.
New element, new seals, bowl back on. The seals come in the box and they are the part people leave in it. A hardened old O-ring is an air leak on the suction side, and an air leak there does not drip — it sucks.
Now the fine filter: unscrew it. Spin-on, like the oil one, and it comes off full of diesel. Tray underneath.
The new one on, by hand. Smear the ring with clean diesel and screw it until the ring touches, then as far as the can says. Some people fill the new one with clean diesel first — it makes the bleeding shorter and it is not possible on every engine.
Open the tank valve again. Same trap as the seacock: you closed it in step one and nothing on the boat reminds you.
And now bleed her, because you have just filled the system with air. That is the next job and it is not optional — a diesel with air in the line will not start, and changing filters always puts air in the line.
The jobs · Bleed the fuel system
A diesel has no spark: it lights the fuel by squeezing air until it is hot enough. Air in the fuel line squashes instead of pushing, so the injection pump cannot build pressure and she will not start. Any time you open the fuel system, you put air in it.
Find the priming lever on the lift pump. A little hand lever on the side of the pump, and on some engines a plunger on top instead. If it feels dead, turn the engine over a few degrees by hand: the cam under it may be at the top of its lift.
Open the bleed screw on the fine filter — the first bleed point in the order of the circuit. Rag underneath: what comes out is diesel and it goes in the bilge otherwise.
Pump the lever until what comes out has no bubbles in it. Bubbles mean there is still air behind them. Watch the froth, not the clock — it takes as long as it takes.
Clean diesel, no bubbles: close that screw and move to the next one. The order is the order of the circuit — from the tank towards the injectors, never backwards, or you push the air you just chased back where it came from.
Now the screw on the injection pump, the same way. Pump, watch, close when it runs clean. On many modern engines this is the last one and the system self-bleeds past it.
And if she still will not start, the last air is at the injectors. Slacken a union, turn her over until fuel comes, tighten it. Ten seconds of cranking at a time — you are spending the battery, and with the seacock open you are also filling the exhaust with water. And that is the one pipe on this engine you treat with respect. The pressure in it is high enough to put diesel through skin, so you slacken it with the engine stopped and you keep your hands clear while somebody turns her over. On an engine with electronic injection you do not slacken it at all — that system holds pressure whether she is running or not, and bleeding it is a job for somebody with the book.
The jobs · Check and tension the drive belt
One belt, three jobs. It turns the alternator, the freshwater pump and the seawater pump off one pulley on the nose of the crankshaft — so when it goes you lose the charging, the cooling and the sea, all at once. That is why it is checked before every trip and why a spare belt is the second spare you carry, behind the impeller.
Engine stopped, isolator off. Your hand is going between two pulleys that turn without warning if the starter gets a stray signal.
Look at it before you touch it. Cracks across the ribs, a glazed shiny face, frayed edges — and black dust on the block underneath, which is the belt wearing away and the clearest sign there is.
Press it with your thumb, midway on the longest run. About a centimetre or two of give is right — much more and it slips, much less and it eats the pump and alternator bearings.
Too slack: tension it by moving the alternator. Slacken its pivot bolt and its adjusting bolt, lever the alternator outwards with a piece of wood —never a screwdriver against the casing— and do the bolts up again. The alternator is the tensioner, and that is why it is the part you take hold of.
Check again, and run her. A new belt beds in and stretches: re-check it after the first hour, which is the step that gets forgotten and the reason new belts fail.
The jobs · The engine will not turn over
You turn the key and nothing happens, or one loud click and nothing turns. Almost always this is a connection rather than a part — and the half of the circuit that nobody checks is the way back.
Start with the switch. Nothing at all — not even a click — is usually the isolator off or the key circuit dead. It costs two seconds and no tools.
Look at the terminals. Green or white powder on a post is resistance, and resistance is where a large current turns into heat instead of turning an engine.
Isolator OFF, then clean them and tighten them. Off first, always: there is no fuse between that battery and the starter, so a spanner across a live post welds itself in place.
Now the half nobody checks: the earth strap. Follow the heavy black cable from the battery to where it bolts to the block. Green powder, a loose bolt, or paint under the terminal will all do it — and the battery will test perfectly on a meter while it does.
Then the heavy positive, both ends. Same treatment: clean, tight, and smeared with petroleum jelly when you put it back.
And if it all checks out, it is the battery or the starter — in that order. A battery that turns cabin lights bright and an engine not at all is still a suspect: lights draw amps, a starter draws hundreds. If you have nothing left, there is one more way to start her, and it is the last job in this part.
The jobs · Hand-start with decompressors
A diesel has far too much compression to turn by hand. The decompressors hold the exhaust valves open so the cylinders cannot build any, and then one person can spin the engine up to speed. Few modern engines have accessible decompressors and few boats carry a handle — but if yours does, this is the only thing that starts her with no electricity at all.
Fuel on, seacock open, gear lever in neutral. The same three as any start, and here they matter more: you are not going to get a second chance at this without a rest.
Lift the decompressors. All of them, and check they have stayed up. With them lifted the engine turns almost freely; with one down you will not get it up to speed.
Fit the handle on the nose of the crankshaft, and make sure it is home before you pull on it.
Grip it with your thumb on the same side as your fingers. Never wrap your thumb round. If the engine fires while the handle is on it, the handle comes back the other way — and a handle that kicks back breaks wrists. A thumb alongside lets it go; a thumb wrapped round does not.
Wind her up to speed. Faster than feels necessary, and keep going — the flywheel is storing what you are putting in, and you need it spinning properly before the next step.
Drop the decompressors while she is still spinning. That is the whole trick: the flywheel's momentum carries her through the first compression, the air gets hot, and she fires. Let go of the handle as you do it.
Take the handle off and stow it. A handle left on a running engine is a thing that spins at engine speed a foot from your knee.
Open the interactive chapter →The same material with the chart, the drawings and the exercises.