No announcement yet.

An education on air compressors

  • Filter
  • Time
  • Show
Clear All
new posts

  • An education on air compressors

    While I try to know, or at least educate myself, on everything motorized, I have a long way to go and learn something new everyday. I really did not know what the function of an air compressor (on an outboard) was, only that it infused air into the fuel and made the engine run mo

    That said, between Charlie at Beavers Marine, our very own Jim Whittman, and a few other website's, I have learned more and more about what it does, maintenance, issues, etc. My 225 Pro XS had a chirping noise (452 hrs.), last Friday that should have told something was about to happen and I took the most easy, economical route of just greasing a fitting. Had I stopped and researched the noise, I probably would not have fished on Sunday, thus saving me a few bucks. So I am posting this to "maybe" save some of you the headache, time and money in the future. Here are the things I have found:

    The Optimax Air Compressor is the "secret" to the Optimax's excellent performance.
    The Air Compressor builds about 80 PSI of air pressure in the fuel rails.
    This is balanced by an air pressure regulator to be 10 PSI less than the fuel pressure.

    Any drop in air pressure will dramatically reduce engine performance.

    The Air Compressor is belt driven. The belt is held tight by use of a Belt Tensioner.
    The belt and tensioner should be inspected on a regular basis for wear or looseness.

    We recommend the belt be replaced every 100 to 200 hours or sooner if required.
    If the belt breaks or if the compressor fails the engine will NOT RUN.

    Most Optimax engines have two small oil lines exiting the air pump (see the yellow covered fitting in the image below).
    There are two small white inline oil filters in these lines.
    These lines allow oil to pass through the pump and to the top and bottom crank bearings.
    These oil line filters should be changed every 100 hours or whenever there is a compressor failure.

    Oil is fed to the compressor from the electric oil injection pump located down on the front starboard side of the motor.
    (see the black fitting cover in the image above).

    The Air Compressor is water cooled. The compressor has it's own alarm temp sender in the compressor head.
    If the compressor overheats it will send off an alarm and put the motor into Guardian Mode.

    Compressors can fail.
    When a compressor fails the engine runs bad or does not run at all.
    In many cases debris from the compressor passes through the air lines into the fuel rails.
    In some cases the debris will contaminate the Air Injectors.
    All lines, rails and air injectors must be meticulously cleaned and/or replaced after a compressor failure.

    Different model Optimax motors use different Air Compressors.

    The air compressor will typically fail prematurely if the pee-hole gets clogged. Understand that when the engine is not peeing, your air compressor is not being cooled. The compressor will last a little while running hot, but the life is shortened.

    It has also been estimated that the air compressor fails around 1000 hours. The bearing is usually what goes. I recommend changing the bearing and cleaning the oil injection screens every 500 hours. You can buy the rod and bearing for about $50. And it takes about 1 hour to replace.

    If you are out in the boat and your start to here the bearing squeeling than its a good idea to shut it down and replace the bearing b/c if you let it fail. Then you have to replace the end cap assembly and bearing at minimum. If the piston fails then you have to replace the whole air compressor to tune of $500-$750.

    The compressor itself can be replaced in about 15 minutes. I think its 4 or 5 bolts. Check the belt and the air filter inside the airbox.
    There are a couple very very small oil filters in the oil supply lines that run to and from the compressor. Replace those and clean out the line between the compressor and filter to remove and metal fragments. Its very easy once you see it.
    You will want to prime the oiling system and put it into "break-in" mode after replacing the compressor. There is a procedure that involves the key switch and moving the shifter in and out of gear a number of times.
    Lastly, a common cause of failure is a blockage of a filter/screen in the cooling line that runs from the port side of the block to the port fuel rail and then to the compressor. Where that line attaches to the block on the lower port side, the fitting contains a screen. Remove that fitting and clean the screen. Its a PITA to get to but dont skip this as it may be why you toasted your bearings. I have talked to Merc techs who had no idea about cleaning out that screen!

    Air compressor failures are most prevalent in the Spring/Fall, when the following factors can/do contribute:

    -Widely varying temperatures
    -Increased moisture and humidity (inconsistent)
    -Boat/Engine has been SITTING (promoting corrosion inside the compressor)

    Since found out that Mercury has gone from a single bearing on their a/compressors to a dual bearing which I will now have.
    2013 Frog Only Tournament Winner
    2010 Tie for VA-Outdoors Angler of the Year
    2009 Caroline County Rotary Club Tournament Winner
    2007 Tuesday Night Classic Champions
    "Many men go fishing all of their lives without knowing that it is not fish they are after."

  • #2
    Alot of dang great info right there. Thanks for posting Larry, and to all who helped ya out. 50.00 vs 500-750...Damn man. Sorry again bud
    Crank That Jank!


    • #3
      Thanks Larry, great info, I printed it out and put it in my Service Manual. FYI, the Mercury Service Manual recommends replacing the compressor air intake filter every 100 hours or yearly and replacing the two oil line filters and the drive belt every 300 hours or three years.

      A friend is a present you give to yourself


      • #4
        Wow - I more along the lines of 'runs mo betta' when it comes to this stuff.

        Still glad sometimes I got the 'old fashioned' carbed XR6

        Glad you got it worked out pretty quick Larry.
        Wishin' I was fishin'...



        • #5
          Thank you California! Nice read Larry.
          2010 VAO Polar Bear Overall Winner
          2010 VAO Polar Bear Big Striper



          • #6
            Where can you buy the parts to rebuild the compressor can not find


            • #7
              Where can you buy the rebuild parts can not find