Fuel filters and bleeding on a Perkins 6.354

Changing the fuel filters on an old marine diesel is twenty minutes’ work. Getting the engine running again afterwards is another matter: you have to get the air out of the system, and that is when you find you can pump for a very long time without anything happening. Here is what we did on CQS Evidence’s Perkins, and above all what the manual says that we wish we had read first.

The engine is a Perkins of the 6.354 family, a six-cylinder diesel, the standard fit on sailboats of this size in the seventies. The procedures below come from the Perkins user’s handbook and apply across the family; torque figures and part numbers should be checked against your own engine plate.

What we did, and what is left

• Done: replaced the fuel filter element
• Done: replaced the pre-filter/water separator, the one that takes the water out of the diesel
• Done: bled the system completely — the long part
• To do: the oil change and the oil filter. The filter is bought, it is waiting.

The fuel system, in order

Understanding the order of the components is what makes bleeding obvious. Fuel leaves the tank, goes through the pre-filter/water separator (where water falls to the bottom), reaches the lift pump — the one with the little priming lever — passes through the main filter, then joins the injection pump, which sends fuel at high pressure to the injectors.

Everything before the injection pump is low pressure. That is where air gets in, and that is where you get it out.

Changing the fuel filter element

The manual is categorical on one point: use the genuine element. An unsuitable element can damage the injection pump, which costs infinitely more than the filter.

1. Clean the outside of the bowl before opening it, so no dirt falls into the system. Drain the bowl through the tap if there is one.
2. Hold the bowl in one hand and slacken the centre bolt that runs through the filter head.
3. Lower the bowl, take the element out, throw it away.
4. Clean the inside of the head and the bowl.
5. Replace the seals and lightly oil them with clean diesel. This is the step people skip and regret: a tired seal lets air in.
6. Offer the new element up square against the filter head, then tighten the centre bolt.

If the filter has two elements, change both at the same time.

The pre-filter/water separator

It sits between the tank and the engine. On a boat it does not just filter: it traps water, and water in a sailboat’s diesel is not a hypothesis, it is a question of time. The manual asks you to check the bowl for water every day or every eight running hours, and to drain it as soon as there is any.

We replaced ours with a Racor FG500-type water separator. It is a good moment to take the opportunity: a separator with a clear bowl lets you see the water without dismantling anything.

Bleeding, or why you pump for so long

This is the part that cost us the most sweat. We pumped, and pumped, and pumped again. The manual explains why, and gives two pieces of information that change everything.

The second piece of information is that bleeding is done in stages, following the order of the system. You never try to push the air from one end to the other: you open one point, pump until the fuel comes out free of bubbles, close it, and move on to the next point further along. Each stage only moves the air as far as the next screw. That is why pumping for a long time at one point gets you nowhere.

1. The fuel filter head. Slacken the bleed screw or the banjo bolt. Pump the lever until fuel comes out free of air. Tighten up.
2. The injection pump inlet. Slacken the inlet union, pump, tighten as soon as the fuel runs clear.
3. Put the stop control to “run” before going on — key to “R” if the stop is electric. Without that, the rest is pointless.
4. The injection pump bleed screws. On a CAV pump there are two: the hydraulic head one, then the governor cover one. On a Bosch, just the one, slackened half a turn at most.
5. The starting aid, if the engine has one: slacken the union, pump, tighten.
6. The injectors. Slacken the high-pressure unions on two injectors, then turn the engine on the starter — not the lever, at this stage — until fuel comes out free of air. Tighten up.

The engine is ready to start.

Watch out too for high-pressure fuel when you slacken the injector unions: it comes out as a fine jet and goes through skin. Never put your hand in front of it.

The parts and what they cost

• Perkins fuel filter element 26561117 — about €10. Outside diameter 88 mm, inside 18 mm, height 72 mm.
• Racor FG500-type water separator, part number 482720 — the complete separator, clear bowl.
• Perkins oil filter 2654407 — bought, to go on at the next oil change.

On the scale of a refit it is trivial: a few tens of euros for the component that decides whether the engine starts on the day you need it. It is the best peace-of-mind per euro on the whole boat. The final total will come once the oil change is done.

The oil change, still to do

We note it here because it is already prepared, and because the manual gives two pieces of advice that save you from a blunder.

• Drain the oil warm, it carries the deposits out better. Sump plug to 34 N·m on reassembly, with its O-ring in good condition.
• Fill the new cartridge with clean oil before fitting it, and let the oil work through the element. Oil the seal. Tighten by hand only — never with a strap wrench.
• Build oil pressure on the starter before firing the engine up, then check the level and look for leaks once it has cooled.

For oil, the manual asks for API CC/SE or CD/SE depending on the version, and a viscosity chosen for the ambient temperature — a 15W40 covers our latitudes comfortably. For fuel: cetane number 45 minimum, density 0.835 to 0.855 kg/l, sulphur content 0.5% maximum by mass.

Service intervals

As Perkins gives them. On a boat it is almost always the interval in months that falls due first, not the one in hours.

What we would do differently

• Read the page about the cam before starting. Three lines in the manual would have spared us a good share of the pumping.
• Bleed point by point from the outset, instead of hoping the air would eventually find its own way out at the far end.
• Change all the seals in one go, not just the ones that look tired. They cost a few euros and they are the first cause of air ingress.
• Have something to mop up with. Everyone underestimates how much diesel ends up in the bilge during a bleed — and in a boat, what goes into the bilge does not evaporate.

The documentation

Everything above comes from three publications. We cite them by their exact reference, because that is what lets you find the right one:

• Perkins 6.3544 Series — User’s Handbook, publication TPD 1289E, 2nd edition, 1994. The owner’s manual: maintenance, bleeding, fluid specifications, fault finding.
• Perkins Service Data Booklet, Part 1, publication TPD 1357E, 1st edition, 1997. The numbers: torque figures, clearances, intervals.
• Massey-Ferguson spare parts catalogue, Perkins A 6.354 engine (MB 500 / MB 510), reference 957 060 M2, 1965. The exploded views and part numbers.

Going further

The engine is only one piece of the refit. The other guides cover replacing the skin fittings, rewiring in 24 V lithium and what to check before buying a second-hand sailboat. The logbook follows the refit month by month, and the budget is public.