Thursday, 17 December 2015

How to bleed a Perkins 4108 marine diesel engine ?

The owners manual gives a good account of the process and really that should be all you require?

Bleeding is the term used to remove air from the high pressure side of a diesel engines high pressure injection pipes, as with air in the system the diesel will not flow and the engine will not run.

The picture shows the engine and in the lower left hand corner is the diesel oil filter, start by opening the top fitting and pumping diesel through with the diesel pumps finger lever, when no air is seen you can close the vent plug off.

There is a catch though, the pictures shown in the manual are without the exhaust manifold and a mass of related pipes and fittings.

This spare Perkins 4108 engine has the exhaust manifold removed and for that reason the bleed screws or bolts are more accessable and easier to see.

The picture below shows the actual vents you need to open.

Look for the three spanners, which are two 5/16" and one 1/2" in size. In practice you will only require one of each size.

Click on the images to enlarge them.

The system should be vented by opening the lower bleed plug first, pump with the finger lever untill there is no sign of air, leave the plug open then move onto the top plug, vent that too until there is no air, leave that one open also.

Then open the nut to the fitting on the right, there will be a pipe exiting there, when no air escapes open the nuts at the base of the four injectors.

Next move the engine throttle control to fully open, with the key crank the engine until diesel comes out of the four injector pipes and with no air.

Then close all the open unions up and the engine is ready for starting.

The manual does not show you what the vent plugs look like when removed, this picture is the upper plug.

This upper fitting is actually a spring loaded piston valve, cracking off the lower 1/2 " nut did not achieve a result. After removal of this spare set of bleed bolts,  I could better understand why?

In practice you will only need to slacken the smaller top bolt to bleed the air out, the bottom one is the one lying loose, it goes into the top of the main fitting and then compresses the spring we can see.

You Do Not Remove The Entire Assembly!  as that was done so that I could better explain what is inside the unit.

Note, you may have to use a 7/16" spanner to hold the center nut in place as you loosen the upper plug with a 5/16" spanner, ring spanners are better than the open spanners for this work.

This is the lower vent plug, check the flat side, that allows the air to vent out when the plug is opened.

All of the above pictures were taken with a Canon G12 digital camera set to Auto.

The Perkins 4104 marine engine shown is due for a full rebuild in 2016, new liners, pistons, crank bearings etc, it has a brand new cylinder head, contact me for pricing.


1 comment:

  1. I’m having a helluva time getting my 4108 bled so I can back in the water.
    Thanks for the better pictures than what’s in the manual.
    After you open the three bleed screws and no air comes out, do you close them before bleeding the injectors?