Shaking at High RPM Running 1955 Evinrude Fleetwin Aquasonic 7.5HP

[frankr]

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

[Good-Fishing]

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]

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]

frankr wrote:

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

Good-Fishing wrote:

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]

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.

[eviltwin]

At full throttle that must have put huge amounts of torque all through it in a nano-second.
The question is where did it get absorbed, and how far up the motor.
I’d even think about looking at the flywheel shear key, not neccessarily pull the flywheel but check for looseness & look at the keyway.
How is the prop shear pin?
You said it starts to buck at full throttle, is that with it IN gear or NEUTRAL?
Sorry for your bad luck, hope you get it solved.

[Good-Fishing]

Ive been running it for quite a while like this trying to fix it. The shear pin is fine. Ive replaced shear pin and the prop same time right after i bottomed out. It bucked in gear at mid to high speed.Kept running it.When it did sometimes it would even out for a minute but then come back again. and flood the shit out of the motor. I didnt rev it too much in neutral to tell. It seems like its only forward.

[fleetwin]

Have a look at the top of the lower driveshaft and its mating surface on the upper bushing/seal housing in the gearcase. You will see wear on the bushing/seal housing where the driveshaft has been rubbing/binding if the shock has expanded cause the lower driveshaft to grow in length. I just want to be sure you have found the issue…Usually, if the shock has been distorted, the symptom will be the engine just seems to bog down/lose power at high speeds because the lower driveshaft is binding on the housing. I have never heard of a damaged shock causing the engine to buck/vibrate wildly like you mentioned…But, I’m sure this could occur if the shock spring is actually broken.
Please check the prop shaft to make sure it is straight, look closely at the gears to make sure there are no chipped/damaged gear teeth. I just don’t want you to put this thing all together and still have the same issue.
Post some pictures of the various parts, perhaps someone will notice something…
And finally, post some pictures of the damaged propeller to help us understand your explanation of the damage…
Be sure to pressure test the gearcase once it is reassembled, you don’t want more water inside…
And finally, it is probably best to replace the lower driveshaft, unless you can successfully weld it in place. Remember, a used piece can have the same issue, so be sure to measure the driveshaft length before using/installing it…D

[Good-Fishing]

Im in the market for a parts motor If you look at the 2 props you can see the difference.

• This reply was modified 4 years, 7 months ago by Mumbles.

[fleetwin]

OK, so is the prop just spinning on the brass hub? Kind of hard to imagine how this could happen, maybe the prop was not machined/assembled properly…Or, perhaps the aluminum is cracked allow it to pull away from the brass hub…
OK, I’m confused….You have one prop labeled as the bad prop, but it looks like a good prop….The other prop is labeled good, and it looks like the one where the brass hub has separated from the aluminum propeller casting…
Does the engine vibrate using either of these propellers?

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