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Bruce Robbins

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Posts posted by Bruce Robbins

  1. Hi Glen,

    The ends are pressed in. They can be removed if you are carefull, but I have never attempted to do so, though I have seen it done. I measure all the pushrods lengths before assembly.

     

    Assemble the heads to the barrels and torque down with NO oil in the lifters so you can compress them easily. Take note what length pushrod went you used. Push down on the rocker at the pushrod end and measure the tappet gap with feeler guages.

     

    The lifters have a working range of 3mm from memory, and I can't remember what that translates to at the tappet end. The idea is to get the lifters somewhere near middle of range if possible. From memory on the last one we did I had about 80 thou as the largest tappet gap with the lifter compressed. Others were zero or close to it.

     

    That's when you get to pull a whole lot of heads off again and swap pushrods around till you're happy that all cylinders have reasonable tappet clearances. If you have already filled the lifters or turned the motor over and pumped up oil pressure, you may need to remove the lifters and pump them on the bench to empty the oil. Some of them seem very reluctant to push down by hand once in the engine and full of oil. They probably bleed down under running loads, but unless you make a tool to compress then insitu, they can be hard to do by hand.

     

    Just as an aside, I have seen a Jab engine fire up and the stop after 1-2 seconds with zero compression. The oil pressure was way above spec, and had pumped all the lifters straight up to max length. Took about two hours for them to bleed back down and get the compression back.

    • Informative 2
  2. Glen,

    It is quite a common problem. Don't risk running with little clearance.

     

    Jabiru supply two different length pushrods. Measure yours and contact them.

     

    You can also shorten the pushrods by removing the ball ends and machining the tube.

     

    I've also heard a few "clattery" Jab motors which i think have the opposite problem. Too much gap for the lifter to take up.

     

    On the last engine we did a top end on we ended up with 10 standard pushrods and 2 short pushrods. 

  3. Barry,

     

    Military Airspace when active is still controlled airspace. (see references quoted by ARO)

     

    So RA-AUS RPC only - No Go.

     

    RA-AUS aircraft and current PPL - Maybe.

     

    Aircraft must meet the requirements and PPL must have the airspace endorsements.

     

    R421 usually closes 12:30 Friday through to Monday morning, so is available to RA-AUS aircraft and pilots. Note that R453 is often still active on weekends, even when R421 is de-active.

     

     

  4. What the standard vane?Interested in how you made it so you could rotate

    Hi Jetjr,

     

    The vane is a modified version of the cobra head fitting that attaches the scat hose to the carby mouth on a standard Jab install. They have fitted intersecting plates that run the length of the cobra head, effectively dividing the tube into 4 sections. Normally you would install the cobra head so that the outlet sits nicely in line with the outlet from the air box, keeping the scat hose run nice and straight.Because it clamps to the carby mouth you can rotate it a little either direction.

     

    search?q=jabiru+cobra+head&ie=UTF-8&oe=UTF-8&hl=en-au&client=safari#imgrc=uBylEhSMh6iPKM%3A

     

    jabiru cobra head - Google Search

     

     

    • Informative 1
  5. By in "front of the distribution box" do you mean between immediately after the carby and before the manifold induction chamber?....... I've already got a crossed baffle on the inlet into the carby. But if yours worked on the outlet might try the same.

    Hi Jaba,

     

    We recently installed a cross vane (from Jabiru) in a roller follower J230. We found that rotating the crossvane produced large changes in EGT behaviour between cylinders. After a fair bit of trial and error we finally narrowed in to a position that gave a nice even spread in both climb and cruise.

     

    Regards,

     

    Bruce

     

     

  6. Tried everything but I think it may be the right carby bowl leaking noticed fuel wet on the outside so l guess on full boost it may be loosing some air pressure which I guess would throw the engine way out of balance as those cylinders would be lacking some fuel , previous owner has overtighned the bowl ,apparently a common problem, now I have to figure how to fix it, maybe some sealer any ideas?

    I have seen a Rotax 914 operating quite normally with a leaking carby bowl, but it is still possible depending on whether it's just leaking or the fuel level is too high causing flooding.

     

    I had a problem with similar symptoms on a 912 UL that turned out to be a faulty muffler. Of course that was the last thing checked, after we'd already turned the carbies inside out several times.

     

     

  7. We'll done Ozzie, that's exactly what is was.

     

    The strong winds on the Saturday blew the exploding fuel onto the grass, starting a grass fire that required the attentions of a couple of fire trucks.

     

    Show was very well done, as is usual for all the Kiwi air shows I've seen. Some world class displays, and plenty of " almost close enough to touch" action.

     

    If you like WWI or WWII action, then block out Easter and head for New Zuland.

     

     

  8. G'day Ozzie,

     

    I'm probably getting into semantics, and definitely off topic, and I'm sure you know all this, but the important point to me is that it is the plane moving through the air, not the air moving relative to the ground, that makes the wing work. Quite a few students and enough qualified pilots to be scary still think of wind in respect of the ground and relate that to how the aeroplane is affected. ( " I need to hold rudder to counteract drift", "I get more lift when I turn into wind" etc etc etc)

     

    Relative wind (which I prefer to call relative airflow) is the movement of air relative to the aeroplane only, with no reference to the ground or any other point of reference. In a dead still air mass ( no wind), an aeroplane flys nicely by moving through the air, thus generating what the pilot in his open cockpit feels as relative airflow.

     

    Wind tunnels reverse this, and move the air past a stationary object, so it is easier to study. This must however distort the behaviour being measured to some extent, because the air now has movement and inertia that it does not have in real life. I rarely fly in 120 knot winds, but I often fly in a 120 knot relative wind. :)

     

    That was the point I meant to make in the previous post. The behaviour shown in wind tunnels by streamlines and staccato puffs of smoke may not be the same as in real life. Daffyd and the aerogeek might be able to show the difference is negligible, but it must still be there.

     

    Going back to my feeble joke. If the plane is attached to the ground by a rope in a 50 knot wind, you can sit in the plane and make it fly nearly as high as the rope is long. Cut the rope and the flying soon stops. It is not the wind that makes us fly, it is the movement of the aeroplane through the air.

     

     

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