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Thread: Mid-section noise

  1. #1

    Mid-section noise

    Hi all,

    I have a Mariner 50hp from 1995 and I have trouble finding why I have got this noise coming through the midsection. It's been like that for quite some time but has been quite noticeable for the past couple months. it sounds like bearing going off.

    What I did:
    . Removed the leg and ran the engine without the leg (plugged water inlet so that I could get water run into the cooling system) - No significant noise of bearings.
    . Bought a second hand gearbox, serviced it - thinking that it could have been the bearing from the gearbox. Still the same.
    . Bought a stethoscope, The noise only comes from the midsection. Checked around the crankshaft/ gearbox, I don't have bearing noise (apart from engine noise).

    My hypothesis:
    . Corroded exhaust tube around the midsection - No more soundproof of the driveshaft due to the corrosion.
    . Exhaust tube vibrating onto the midsection.

    Here is a video of the noise I am talking about: (check at 6 seconds)

  2. #2

    Re: Mid-section noise

    Sounds like bearing noise to me but were you have looked everywhere I thought of ,there's not a bearing on the shaft some were in the mid section try and find some schematics for the leg.

  3. #3

    Re: Mid-section noise

    Nothing to do with the impellor or housing?

  4. #4

    Re: Mid-section noise

    Maybe a crook engine mount?
    I have a similar type of noise, but on a smaller outboard. My theory is it's the bottom crankshaft bearing, as it's a bit quieter without the gearbox attached, which I put down to the lack of load from the gearbox!

  5. #5

    Re: Mid-section noise

    Thanks for the replies

    I thought of the bottom crank shaft beating but it does not make much noise with or without the leg. I used the stethoscope for investigating. I really do hope it's not the crankshaft bearing....

    I dont believe it would be the impellor or housing as it clearly is a bearing noise.

    There is no bushing or bearing in the midsection.

  6. #6

    Re: Mid-section noise

    It definitely sounds like a ball bearing race wearing out but there is no way of testing the lower crankshaft bearing unless u remove the power head, You may be able to place the stethoscope down inside the lower cowling right up against the base powerhead gasket seal and see if u can hear the bearing but it's likely u wont be able to hear the bearing as its centralized on the block the way the stethoscopes work is the resonating sound that travels from a item like a bearing thru the housing holding the bearing and u have the stethoscope on the outside of the housing you just dont have that access

    there is only one way to fix it and that is to remove the powerhead and disassemble it removing the crankshaft u need to press the bearing off if its a ball bearing as i suspect it to be, Such a shame a $25 bearing can cause catastrophic failure if u keep running it

  7. #7

    Re: Mid-section noise

    1995...Carlton won the last of its current 16 premiership cups....Koota played well ...but Williams and some blow in Centre half forward from the Demons...awesome..So that is history and frankly once you start taking apart a motor from that era.........Its probably going to get to the stage where you do a lot more than fix one while your in there..personally no problem going that way but be prepared...


    you make an ass out of U and me...

  8. #8

    Re: Mid-section noise

    So you guys reckon I continue like this until failure? Or take the challenge of changing the bearings. I have the service manual and it seems not too bad. just lots of elbow grease.

    I have planned to re power for summer to be honest.

  9. #9

    Re: Mid-section noise

    Quote Originally Posted by Tyfab14 View Post
    So you guys reckon I continue like this until failure? Or take the challenge of changing the bearings. I have the service manual and it seems not too bad. just lots of elbow grease.

    I have planned to re power for summer to be honest.
    If it's not a new noise, or getting worse, then just keep using it till you get the new one. Unless your happy to spend a few hundred dollars for the bits to fix this one, not sure if you'll get that money back when you try to sell the old one!

  10. #10

    Re: Mid-section noise

    I would only repair it if u plan on keeping the engine or if u need more money when u sell it to buy the new engine, if u do sell it as is be honest to the new buyer and tell him/her of the suspected bearing racing noise

  11. #11

    Re: Mid-section noise

    Thanks for the reply. I am keen to go ahead to change the bearings. So Gazza, do you believe itís the bearings crankshaft? (Top/bottom). I found new genuine parts for $150 top and bottom bearings (+$40 for the bearing press tool).

    I also bought new bolts for the power head they are so rusty ... fist surprise by only removing the bottom cover ... wish me luck!

  12. #12

    Re: Mid-section noise

    Trade it in mate.

  13. #13

    Re: Mid-section noise

    Ty u need a hydraulic press u need to put a plate between the last crank web up against the shaft to press the new bearing onto the shaft similar to my picture i had to press this bearing onto a shaft the other day for a project, u should be able to pay a shop to change the bearing it should only cost about $50
    Attached Images Attached Images

  14. #14

    Re: Mid-section noise

    At least pull it apart first before you order any new parts. As well as a new base gasket etc., if you do end up with say, a rotten exhaust tube, your going to be spending whole lot more than it's worth!

  15. #15

    Re: Mid-section noise

    Thanks guys for the tips. I think itís a good idea to first pull appart the power head to the midsection and see what is happening. I still believe itís the exhaust tube. But if not, Iíll pull appart the power head and see the bearings condition.

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