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  1. #1
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    Question 175 EFI no prop movement & loud metallic engine noise.

    2000 Mercury 175 EFI: had been running all day up to WOT without issue and engine shifting smoothly. I dropped my partner off at ramp and took off to give her one last final run before her winter nap. Hit 5600 RPM & 61 mph with a 23 pitch Trophy 4 (not Trophy plus) and suddenly heard loud bang and thought engine blew, but RPM stayed at/near same and engine did not die and idled fine.

    A very loud metallic clang began coming from engine in gear but again RPM range was fine. I trimmed the outboard up and to see the prop and prop did spin slowly in gear for a moment and then stopped spinning after about 5 seconds when submerged. Motor did the exact same thing in reverse too, just spun just a few seconds and the stopped when submerged and then spun no further in either direction in gear.

    Trolled to ramp and checked gear oil; there were some metal shavings on magnetic drain plug but not excessive, no water flowed out when plug was removed but lower unit oil level was low about 1/3 full and oil looked more aerated then having water intrusion and no additional metal shavings were drained out.

    The motor seems to be running fine except it will not spin the prop and it's making one heck of a noise in gear. I thought if you grenaded your lower unit, your motor would die but it never did? I've never spun a hub before so I have no idea if that would clang loudly? The prop itself is fine it's not hitting anything. I didn't think to put it in gear and try to turn it or check for spun hub.

    Questions, did I blow it up, break a drive shaft, or simply spin a hub (flo torque) if so would it make such a loud metallic clanging noise? Any other causes it may be? I put it away for winter after putting in new gear oil in and put it in the storage locker. It's some 200+ miles from my home and there it sits. If I go down in a couple of weeks, what & how should I check to determine the issues?

    Thanks!

  2. Member Bass AHolic's Avatar
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    #2
    I'd take it off LU and bring it home, and if needs fixed have it done during down time. with That said is all I can contribute, I despise assuming..

  3. Member
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    #3
    normaly when you spin a hub no noise is heard /I would have bearing carrier removed for inspect of pinion gear and internals
    .................................................. ...the scariest thing in life is the unknown ...................................

  4. Member dwtaylor's Avatar
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    #4
    If it is only making the noise in gear, I would bet that your driveshaft is fine. Could be a few things:

    -Clutch dog teeth worn/missing on either the clutch and/or the forward and reverse gears. These teeth translate torque from the gears to the clutch to the propshaft.
    -Broken propshaft inside the gearcase.
    -Broken cross hole pin on the clutch.

    The driveshaft, pinion, forward and reverse gears are always rotating in the gearcase regardless of being in gear or not. I don't think that you have a bearing seizing up either because that could bug down your powerhead and nothing with move. Running that gear oil that low could cause issues with premature wear inside the gearcase. 1/3 full is too low and if it was running like that for some time, it could be the root cause of this failure.

    Definitely inspect inside the gearcase by removing the bearing carrier.

  5. Member
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    #5
    It does sound like you might have broken the drive shaft.
    The description of the lower unit oil does not point to a cataclysmic internal failure, though the oil level is of concern. Not sure how you lose oil without seeing it.
    The upper bearing at the top of the gear case would likely be the one that starved for oil, seized, and took the drive shaft with it.
    Michael Martin
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  6. Member
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    #6
    Thanks everyone for the excellent observations; I'm going to try and diagnose it further in the weeks to come prior to engaging the shop. I recently bought this motor rebuilt from a reputable person and when I asked of the lower unit condition I was told it was only one year old and in great condition. I made a foolish assumption the gear oil was OK and never personally checked it. The irony is, although I observed no leaks in my storage area I had still intended to put brand new gear oil in prior to my trip, but forgot to grab the items when I left home.

  7. Member
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    #7
    I'm betting on clutch dogs. Why? prop slowly spins but stops when submerged. If the clutch dog ears get ripped off, you simply have metal-to-metal contact trying to spin the prop. Be interesting to hear what the final outcome is.

    You could try to carefully shift into forward (not cranked, boat on trailer). If it shifts easily, you are into clutch dog failure area (the only way it will allow this normally is if the clutch dog teeth happen to be in alignment, not so common). with it in gear, spin prop by hand. You should not be able to do so. If you can, certainly something in the lower unit has failed catastrophically. Remove bearing carrier and prop shaft and the problem will most likely be obvious.

    Unfortunately, I have no idea of how the clutch dog gets the teeth sheared off if you didn't either hit something, or else put it in gear at 5000 RPM.
    Last edited by OldTimer57; 01-04-2017 at 09:05 PM.

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    #8
    Thanks for the suggestions: I'll follow up in the weeks to come.

  9. Member straffordengineer's Avatar
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    #9
    Sounds like something internal to the lower unit. If the input shaft broke before entering the lower unit the water pump would not be running and the engine would overheat. This is not a simple fix. Remove the lower unit and take it to a repair center.

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    #10
    Thanks, the boat is in storage near you at: Stockton Lake. If you have any lower unit repair shops you may recommend in your area, please shoot me a PM.

  11. Member
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    #11
    Quote Originally Posted by straffordengineer View Post
    Sounds like something internal to the lower unit. If the input shaft broke before entering the lower unit the water pump would not be running and the engine would overheat. This is not a simple fix. Remove the lower unit and take it to a repair center.
    good advice indeed
    .................................................. ...the scariest thing in life is the unknown ...................................