Loud tapping noise after water ingress

Discussion in 'Technical' started by Chev28, Jan 5, 2015.

  1. Chev28

    Chev28 Member

    Bad news.

    I recently had the balance tube off and accidentally knocked some water into the plenum (don't ask how). I thought I had got it all out and refitted the balance tube.

    I then started the engine and it blew a bit of steam out and black muck out the exhaust and then ran OK.

    However, the engine then developed a loud tapping sound at the rear of the plenum (ie at the top of the engine). The noise rises and falls with the revs. The engine seems to run OK just with this really loud tapping/ticking noise.

    I put the stethoscope onto each injector and heard them all OK except for No 6 which seems much quieter. Again, though, the engine is not running rough.

    What could be causing this loud tapping noise? Could one injector be affected by water? I don't want to drive it until I know it won't cause further damage.

    I don't believe it is lifter noise as I can't see how any water would have gotten across to the oil.

    Please help!
  2. mungyz

    mungyz Well-Known Member

    Post a vid of the noise for a better chance of a good diagnosis BUT sounds like a bent rod or cracked piston due to hydraulic lock.
  3. Chev28

    Chev28 Member

    Will do but how could it hydrolock if the engine didn't actually stop?
  4. Chrispy

    Chrispy Pretentious Upstart

    Can still bend a rod without stopping the engine...
  5. pmac

    pmac Z,, IT'S COMPLICATED!!!!!


    How much water are we talking about?
  6. kickerzx

    kickerzx Member

    Not much help now, but for future reference. If you ever suspect water or any fluid in the plenum again, take out the plugs before you cranck it. This way you would have blown any fluid out the plugholes...
  7. Chev28

    Chev28 Member

    Thanks. I thought I got it all out of the plenum but in hindsight should have pulled all the plugs too.
  8. Chev28

    Chev28 Member

    Can't seem to get a good recording of the noise.

    Another way to describe it is a bit like the loud timing chain rattle of an old Magna (for those who remember)
  9. Chev28

    Chev28 Member

    Just been to the local mechanic. It's stuffed.

    Time for a new engine.

    I just spent most of the weekend replacing the driveshaft and replacing the injector and plug connectors. Not sure I have anything left for an engine R&R right now (plus I just can't get my head around the job itself).

    Does anyone know an experienced Z mechanic in Western Sydney who can do an R&R in reasonable time? Seems like the general mechanic hasn't done one.
  10. SRB-2NV


    If your mechanic cant fit a new engine for you i wouldn't go back there. I did my tt conversion at home with limited tools. Man a zed is piss easy to work on once you've had to do everything yourself :p
  11. Fists

    Fists Well-Known Member

    I think he was talking about engine building which is reasonable for a general mechanic to not do. If we take your comment as recommending just fitting another working engine then I agree.
  12. Chev28

    Chev28 Member

    It's not that complicated. I normally do everything myself but I just can't find the time and need this fixed soon.

    I went to the local mechanic to confirm the noise. He was OK for that help but admitted he hadn't done a 300zx engine pull before so I just don't want to go down that path.
  13. Madcow

    Madcow Active Member

    Keep looking. You dont wanna pay for them to learn.
  14. East Coast Z

    East Coast Z Well-Known Member

    What did the mechanic say the problem was?
    Have you performed a compression test?
    You're not going to get a great deal of water into the plenum via the holes with the balance tube off.
    Are you sure you didn't drop something into the plenum like a nut or bolt?
    There's no point listening to injectors clicking, that'll tell you sfa.
    If you really want assistance with this problem, it would be in your best interest to answer the questions people are asking.
    For instance an unanswered question that may have the most relevance to your issue is, "how much water went into the plenum?"
  15. Chev28

    Chev28 Member

    Thanks but I think we have it diagnosed. Sound is in time with piston, not cams so looks like hydrolock scenario and bottom end damage.

    Debating the quantity of water seems pointless. Probably half a cup or less of water went in but can see no alternative unless you can suggest another tapping noise that develops from only a small quantity of water?

    Really just focussed on finding a decent NA engine at the moment to get back on the road.
    Last edited: Jan 7, 2015
  16. Martin Williams

    Martin Williams Well-Known Member

    I am sure you have done some damage with the water ingress, but from what you have told us its limited to 1 piston or valve/bearing. Probably , piston, rings, bearing or conrod, none of which are expensive on their own. I would repair the engine you have.
    $2k in my limited workshop. Then you would have a known good engine.

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