Results 1 to 5 of 5
  1. #1
    Member
    Join Date
    Mar 2005
    Location
    lockport
    Posts
    37

    1999 Merc 90 ELPTO knocking from midsection

    I bought a 99 Merc 90 ELPTO for my pontoon that the previous owner said was blown. I checked and it had 125 psi on all three cylinders so I figured it can't be that bad. After installing it I ran it on the hose and you can hear a knocking sound that seems to be for the midsection. When I put my ear up to the midsection it's loud. Before I drop the lower unit and try to run the engine pressing the hose up to the tube I was wondering if anyone had any suggestions. I guess I need to figure out if it's the powerhead or lower unit that needs work. Is there anything in the midsection that could cause the knocking? Thanks

  2. Member
    Join Date
    Aug 2020
    Location
    Wisconsin
    Posts
    62
    #2
    There's nothing in there that can knock. All you have is a shift shaft, water tube, driveshaft and exhaust housing in there. Unless the driveshaft is bent, which I highly doubt.

    Some things off the top of my head that I can think of - broken tooth on a gear in the lower unit - transferring the sound up to the middle section. Loose zinc annode rattling on there. In the powerhead, maybe transferring the sound down, broken piston skirt, shelled out wrist pin bearing (rollers gone in it), seen one with a broken crank once and it still ran. Although the one with the broken crank, could grab the flywheel and rock it back and forth and it would clunk every it was rocked.

    I'd just pull the lower unit, hook water up to the tube and run it to narrow it down.

  3. Member
    Join Date
    Mar 2005
    Location
    lockport
    Posts
    37
    #3
    I ran the motor without the lower unit today and I couldn't hear the knocking like when the lower unit was on. I am still not positive it's not the powerhead but looks more like the lower unit. I put it all back together and think I'm just going to run it until it breaks.

  4. Member
    Join Date
    Aug 2020
    Location
    Wisconsin
    Posts
    62
    #4
    Why not, as long as you got the lower unit off, pull the screws, bearing and seal housing and prop shaft and see if you got a worn clutch dog or busted gear? No sense to punching a hole in the lower unit housing because of a potential broken gear tooth that gets picked up in the oil and run thru the wringer. At least then you know what you got.

  5. Member
    Join Date
    Jun 2013
    Location
    LONGVIEW TEXAS
    Posts
    13,941
    #5
    pull bearing carrier look inside pretty easy, dont loose 3 balls in prop shaft
    .................................................. ...the scariest thing in life is the unknown ...................................