Shaking at High RPM Running 1955 Evinrude Fleetwin Aquasonic 7.5HP

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This topic contains 37 replies, has 9 voices, and was last updated by fisherman6 fisherman6 1 week ago.

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  • Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183549

    So this summer i was running full throttle and had a log strike with my outboard. Ouch… Ive installed a new prop since I the pulled the weeds out from in/behind shaft bearing . Somehow i’m getting water inside the lower unit now. Where should i start, It still runs great at low rpms however when i go to mid to high rpms it bucks crazy like it wants to jump off the boat and no its not an air pocket. Im thinking pinion shock or warped shaft? Yay. Running 1955 Evinrude Fleetwin Aquasonic 7.5HP

    bobw
    bobw
    US Member - 1 Year
    Replies: 640
    Topics: 28
    #183561

    Since you are now leaking water into the gearcase, it sounds like a bent prop shaft. Prop shaft seal could also have been compromised by fishing line or excessive weeds.

    Bob

    1954 Johnson CD-11
    1956 Johnson RD-18
    1958 Johnson QD-19
    1959 Johnson QD-20

    • This reply was modified 1 month ago by bobw bobw.
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    garry-in-tampa
    Lifetime Member
    Replies: 3204
    Topics: 30
    #183568

    1954 & ’55 were the first Aquasonics and used springs for isolation. In 1956 they switch to rubber mounts, It sounds like a serious mis-alignment issue. Many of these issues are caused by backing into curbs while trailering with the motor down. Minor hits may be straightened. Major crashes will require replacing parts.











    frankr
    frankr
    US Member - 1 Year
    Replies: 4471
    Topics: 43
    #183571

    Bucking like it’s going to jump off the transom sounds like a worn out cutch dog to me..

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183576

    In regards to the spring alignment. I tried this first and went ahead and replaced the springs. Still no improvement. It still shifts smooth. I have the lower unit apart now . Just getting to the gear case. No metal shavings in the oil so that’s a good sign.Just not sure if i have to replace the prop seal or something else.

    Mumbles
    Mumbles
    Canada Member - 2 Years
    Replies: 4200
    Topics: 425
    #183589

    Are you sure the replacement prop isn’t bent to? A bent blade which causes vibration like you describe can be hard or impossible to see visually. A bent propeller shaft should be obvious while turning it with or without the prop on.

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183591

    Just finished pulling the gearcase. Everything looks alright besides the bearing which was obviously letting the water in so i pulled it. The only trouble the bearing gave me coming off was at the end of the shaft where you place the cotter pin it was sticking. Other than that no problems and it looks straight. The prop i bought NOS in original box because the other one was ruined. Since when you use the old one it just spins and you dont move.

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183596

    Just pulled The lower unit shock absober. Its stuck and wont move. Tried moving it in vice and with blocks of wood seems like its locked up pretty good probably going to need a new one im thinking that’s the issue.

    fisherman6
    fisherman6
    US Member - 2 Years
    Replies: 1774
    Topics: 39
    #183597

    Just finished pulling the gearcase. Everything looks alright besides the bearing which was obviously letting the water in so i pulled it. The only trouble the bearing gave me coming off was at the end of the shaft where you place the cotter pin it was sticking. Other than that no problems and it looks straight. The prop i bought NOS in original box because the other one was ruined. Since when you use the old one it just spins and you dont move.

    When you are referring to the bearing I’m assuming you are referring to the prop shaft bearing head which contains the prop shaft seal. Could you tell if the water was getting past the shaft seal or between the bearing head and the gearcase? There is always a burr on the prop shaft where the drive pin and the cotter pin go through. I always file them off first to prevent gouging the shaft bearing and possibly damaging the shaft seal if it is still serviceable.

    When you say the old prop was ruined because it just spins and you don’t move, I’m not sure what you mean. Does the propeller spin when the motor is in gear and running and it just will not push the boat? is the propeller just spinning around the prop shaft and not turning in the water? I’m assuming it must be the first scenario since there is no rubber hub or clutch in this prop, only a drive pin that passes thru a hole in the center of the hub extension and the prop shaft. There is a strong possibility that you may have sprung or broken the shock absorber in the top of the gearcase. These things tend to get more brittle as they age. If this is bent / broken / rubbing the bottom of the drive shaft bearing carrier that may be causing some of your vibration also. When these break I squeeze them back together in a vise or a press and weld the seam together. This eliminates the shock absorber effect and necessitates replacing the steel drive pin with a brass shear pin to protect the gears, but it will not destroy the bearing carrier for the drive shaft and it will not break unexpectedly in the middle of the lake and leave you stranded. While a shear pin is not the easiest thing to change on the water, it can be done and you can get back home. If the shock abosrber breaks you will be rowing or getting a tow.
    -Ben

    OldJohnnyRude on YouTube

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183599

    Yes i was referring to the prop shaft bearing and seal. The water was going through the behind the prop into the gearcase you could tell by looking at the bearing,it was lopsided. The prop is a aluminum and bronze prop. It got caught in the weeds and the bronze part was wore off. These specific props dont work without the bronze part.

    frankr
    frankr
    US Member - 1 Year
    Replies: 4471
    Topics: 43
    #183603

    Dang, you must have some tough weeds to wear that prop hub off.

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183605

    Well, It all happened around the same time with a boat full of people. So i had no choice but to Run it back to the ramp against the current.

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183623

    This is a good thread here. Describing the same things. My shock absober has expanded just short of 7inches. https://aomci.org/forums/topic/7-5-and-5-5-omc-lower-units/

    fisherman6
    fisherman6
    US Member - 2 Years
    Replies: 1774
    Topics: 39
    #183647

    Dang, you must have some tough weeds to wear that prop hub off.

    I was thinking that must be one heck of a 7.5. I have a couple that run great and I’m betting neither of them are strong enough to separate the bronze hub from the aluminum prop on a stock OMC semi weedless propeller.

    -Ben

    This is a good thread here. Describing the same things. My shock absober has expanded just short of 7inches. https://aomci.org/forums/topic/7-5-and-5-5-omc-lower-units/

    If your shock absorber has expanded that needs to be fixed before it ruins the drive shaft bearing carrier. Some recommend to just squeeze them back together and run them again. Sometimes that works. IMHO, if it failed once it will fail easier next time and it may be a total failure at the worst time. I weld them together after squeezing them back down. It only takes a few good tacks around the seam to hold them solid. Then use a brass / bronze shear pin to protect the gears. A steel pin will hold when a brass one won’t but you run the risk of breaking the gears and then you are out of business.

    -Ben

    OldJohnnyRude on YouTube

    Good-Fishing
    Good-Fishing

    Replies: 19
    Topics: 2
    #183650

    Squeezed it back to 6 and 3/4 wouldnt go anymore and it snapped the base of my vice. So then I Used a hydralic jack and it snapped under pressure. Unusable.

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