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Calling all boat mechanics

Scribbles

Scribbles

Paul
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I know we have a couple of boat guys in here.

I have a ‘97 Cobalt 20’ with a Volvo Penta 5.7 TBI and a DP-S drive (Duo prop)

My issue is the drive hub on the flywheel is stripping out or melting really (see attached pic) I had hit something underwater and the next time I took it out the hub failed in about 30min I chocked it up to a delayed failure from being stressed. I pulled the motor, replaced it with an OEM Volvo Penta hub and I would be surprised if I had 4 runs total, I took it out this weekend and after about an hr of tooling around it started slipping when I tried to run it over 3k RPM’s, opened the motor compartment and sure enough smelled rubber. :doah:

What do you think is causing this, the drive u-joints are good, I didn’t hit anything, I’ve never seen one of these fail and now I have two of them personally. It’s really annoying pulling an inboard to get to the flywheel. The motor isn’t overheating, I knew the previous owner well and would have known if he had the issue and he used it for 3yrs before I got it. The only thing I can think of is motor alignment? But the drive shaft slips right in.

@ryoken

01972BA3-A7D7-4C83-A0BE-7B1F1C204FC9.jpeg
 
when you hit something in the water what was the damage to the drive? Did you need new props?
 
skunked said:
when you hit something in the water what was the damage to the drive? Did you need new props?
Click to expand...

No, it knocked the speedo pickup off the transom, it may have dinged a prop but if it did it was very minor. I was also going 10mph tops, not even on plane.
 
Scribbles said:
No, it knocked the speedo pickup off the transom, it may have dinged a prop but if it did it was very minor. I was also going 10mph tops, not even on plane.
Click to expand...
From what I know about boats, which isn’t a lot, the props are very precisely balanced. So any dings or bent blades can cause vibrations.
 
when you re-installed the drive, did it slide in easy?
 
Scribbles said:
No, it knocked the speedo pickup off the transom, it may have dinged a prop but if it did it was very minor. I was also going 10mph tops, not even on plane.
Click to expand...
Did you change the propeller?
If not, then that's your problem
 
rampage said:
From what I know about boats, which isn’t a lot, the props are very precisely balanced. So any dings or bent blades can cause vibrations.
Click to expand...

imiceman44 said:
Did you change the propeller?
If not, then that's your problem
Click to expand...

I did not change them, I’ll look at them just to remind myself what they look like but I would have thought they’d have to be bad and I’d feel it in the boat to ruin a flywheel drive hub. Interesting thought.

ryoken said:
when you re-installed the drive, did it slide in easy?
Click to expand...

Easy peasy.
 
Scribbles said:
I did not change them, I’ll look at them just to remind myself what they look like but I would have thought they’d have to be bad and I’d feel it in the boat to ruin a flywheel drive hub. Interesting thought.



Easy peasy.
Click to expand...
Yeah these propellers spin at a very high speed and need to be perfectly balanced.
If there is any evidence it was hit change it
You started having trouble after the hit so that is it
 
imiceman44 said:
Yeah these propellers spin at a very high speed and need to be perfectly balanced.
If there is any evidence it was hit change it
You started having trouble after the hit so that is it
Click to expand...

I can’t argue with you. :dunno:
 
There is no mistaken what a bent prop feels like. I’ve either bent one or been on a boat with a bent one many times lol
 
skunked said:
There is no mistaken what a bent prop feels like. I’ve either bent one or been on a boat with a bent one many times lol
Click to expand...
There's bent that you feel and then there's just out of balance enough to create damage down the line.
If there is no scratch or chips then it's something else
 
Just saw this, sorry I didn’t chime in sooner! First of all... I’ve seen aluminum, brass, and stainless props ran on boats that are beat worse than you can imagine, and none of them have caused a failure down the line. I’ve seen them ran long enough to burn the paint off and/or pit the metal from cavitation, so I would be willing to bet that this is not the cause of a dinged prop. Another thing is, Volvo Penta drives are ridiculous when it comes to strength, so hitting something at a low speed like you said happened could have definitely led to the first drive coupler failure by shockloading it, or the motor could have shifted and put pressure on the coupler and when the new one was installed it might have just “landed” in the same place. It’s hard for me to say because obviously I’m not there to diagnose the issue with my own eyes, but that’s what I’m thinking. As for anyone that might tell you “if it’s out of alignment it’s hard to get the drive back on” they are only partially right. The gimbal bearing itself will move inside the aluminum retainer, and most times a good shove is all it takes to get the shaft in. Laugh it up guys... I couldn’t find any other way to say it!
So all of that being said, what I would do is pull the drain plug and the vent out of the drive and make sure there isn’t anything in the oil as far as chunks or metal flake (be sure to fill with full synthetic from the bottom hole. You probably know this) if that checks out I would say it is an alignment issue. It wouldn’t be a bad idea to check the gimbal bearing. Usually you can hear it when it’s running but reach in and check it by hand to make 100% sure it’s good. Make sure the wood under the motor mounts isn’t rotten too.
Good luck man. Idk if this helps any but that’s my opinion on this one. In all reality the failure and the impact could be totally coincidental.

B. Bust
O. Out
A. Another
T. Thousand
 
i would concur about the prop, i have customers that run around with banged up props for yr's without losing a coupler...

that's why i asked him how hard it was, implying an alignment issue.. trust me, i install enough every yr, and a big ol block of wood and a sledge are often needed to pop em in.... and that means it has an alignment issue... that's why when i do motor installs, i always align the engine, i have the tool,... it's super common for the front to be down from settling...

I have seen a gimble bearing do it too, but it's pretty rare as usually it'll be growling so bad at point, you can't ignore it.. unless it seizes.

i will admit 9 out of 10 drives i do are bravo/alpha, I don't see a ton of volvo stuff, but it's pretty rare we lose a merc coupler...
 
ryoken said:
i would concur about the prop, i have customers that run around with banged up props for yr's without losing a coupler...

that's why i asked him how hard it was, implying an alignment issue.. trust me, i install enough every yr, and a big ol block of wood and a sledge are often needed to pop em in.... and that means it has an alignment issue... that's why when i do motor installs, i always align the engine, i have the tool,... it's super common for the front to be down from settling...

I have seen a gimble bearing do it too, but it's pretty rare as usually it'll be growling so bad at point, you can't ignore it.. unless it seizes.

i will admit 9 out of 10 drives i do are bravo/alpha, I don't see a ton of volvo stuff, but it's pretty rare we lose a merc coupler...
Click to expand...
Why do we do this to ourselves???
 
FWIW... I’d say 25% of the stern drives we see are Volvo, and other than the old Volvo junk we have only had one major drive failure, BUT.... it was because it was ran without oil. They’re a lot tougher than a mercruiser.
@ryoken I made the mistake of hitting a bravo II in the wrong spot and cracked the shifter housing (not sure exactly what it’s called) and it ended up being a $500 mistake. Lol oops!
 
I’m thinking I’m going to try to check the motor alignment and hope that it’s a freak accident. I did check the gimble bearing when I had the drive off last year and the boots are all good so it shouldn’t be bad. I’m gonna try to go by and snap some pictures of the props but I’m with the others, I’ve seen some really bad props and that’s why those never crossed my mind.
 
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