Piaggio Ape diesel leak

The familiar and unpleasant smell of diesel was coming from the engine bay on this 2014 Piaggio Ape Classic 400, so I started looking for the leak.

Picture of the front left view of a 2014 Piaggio Ape Classic 400

Finding the Piaggio Ape diesel leak

Thankfully it didn’t take long to find! The leak was coming from the fuel return hose, which has solid and flexible sections. The leak was coming from the small flexible section between the 2 solid banjo bolt connections. If you’ve ever watched one of these single cylinder Greaves diesel engines running, you’ll appreciate the hard life that a flexible line might have, due to vibration.

Picture of the flexible section of the return line that caused the Piaggio Ape diesel leak

The Ape had covered less than 1000 km, but alas that was enough for this diesel pipe.

Luckily a new genuine Piaggio replacement pipe was available and not too expensive.

Tools used for the Piaggio Ape diesel leak repair

  • 12 mm flare nut spanner. Not essential, you could use a socket but try to make it a 6 point if possible rather than 12. If you’re in the market for a nice flare nut spanner, these ones are excellent.
  • 7 mm and 12 mm socket with 1/4″ ratchet and extension
  • Torch
  • Compressed air and blow gun (not essential)
  • Rags

Removing the Ape diesel pipe

Removing the cause of the Piaggio Ape diesel leak was fairly simple.

I made sure the tank wasn’t full to the brim before starting. This is because if it was really full (i.e. up into the filler neck), then fuel could come out of the return line spigot when the pipe was removed.

Starting at the tank end, I removed the hose clip from the return line. These usually need a 7 mm socket. I prefer to use a socket than a screwdriver as there’s much less chance of chewing up the head of the hose clip. Let’s just say some of the parts used on the Ape aren’t of the highest quality!

With the hose disconnected from the fuel tank I threaded it back into the engine bay.

Next are the 2 banjo bolts connecting the return pipe to the rest of the fuel system.

Before tackling these, I used some compressed air and rags to ensure the area was as clean as possible, to reduce the risk of introducing contamination to the fuel system.

I used a 12 mm flare nut spanner to undo the top banjo bolt and I made sure I had a rag in place to catch any leaking fuel. There wasn’t enough clearance for the spanner on the lower bolt so I used a 12 mm socket with 1/4 inch ratchet and extension.

With the 2 banjo bolts loosened, the offending fuel hose could be removed.

Fitting the new diesel return line

After a quick check that the replacement line was the same, I started to thread it into place.

I installed the lower banjo bolt first, just a couple of turns to start with. This helped hold the pipe in roughly the right place, which made the upper bolt a lot easier to install.

New aluminium washers were used on both sides of each banjo bolt.

Picture of the banjo bolt on the Piaggio Ape diesel return line.

Finally the end of the hose was reconnected to the tank. I used a new hose clip as the threads on the old one seemed to be slipping as I tightened it.

Priming and starting after the Ape diesel leak repair

The last step was to pump the manual priming lever on the diesel pump a few times. I’m not convinced that this was completely necessary as we’re dealing with a return line rather than a feed line, but I did it all the same.

If you ever manage to get loads of air in the fuel system, there is an air bleed bolt on top of the diesel filter housing, that can be used along with the manual priming lever to remove air from the fuel system.

Picture of the Piaggio Ape diesel fuel priming lever

With the fuel system primed it was time to fire up the beast and check for leaks. I gave it a good inspection whilst idling in the garage, then took it out for a road test and checked it again for leaks after that.

There weren’t any leaks and the diesel smell had gone, so that was the Piaggio Ape diesel leak fixed!

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One comment

  1. Wow, what a detailed and clear report!!! I have a leck in the fuel return hose. So it helps me a lot … ! Thank you so much!!

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