Vibration under load

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firecapt13

Seaman
Joined
Mar 13, 2010
Messages
57
1992 Wellcraft Mercruiser 4.3 Alpha 1 Gen II.

After all my work took it to lake today for test run and i have a vibration under load. I have replace gimbal bearing and u joints looked fine and greased them. They felt smooth with no stiffness. There is no vibration when I idle up to 4000, only when I take off and put in under load. It appears to be constant but a little worse under higher rpms.

The prop is a 4 blade plastic prop with a slight knick in one blade. It has some adjustment marks on it but know nothing about this prop.

What are some things that would cause a load vibration, If it were ujoints wouldnt they vibrate when you throttle up with no load?
 
bruceb58

bruceb58

Supreme Mariner
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Mar 5, 2006
Messages
30,478
Re: Vibration under load

I would suspect that prop. Why are you using a plastic prop?

Did you check alignment of your engine/gimbal bearing before you put the drive back on?
 
F

firecapt13

Seaman
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Mar 13, 2010
Messages
57
Re: Vibration under load

Plastic prop was on it when I got it and yes the marina checked the alignment when they put in the bearing. I have done all the work my self except installing the gimbal bearing, i did not want to mess it up.
 
Don S

Don S

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62,321
Re: Vibration under load

If it were ujoints wouldnt they vibrate when you throttle up with no load?
Click to expand...

Not necessarily. Does the vibration change with trim up or down, or turning left or right?
 
cedarjunki

cedarjunki

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Aug 23, 2007
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Re: Vibration under load

i second the prop.. just how slight is the nick?
 
cedarjunki

cedarjunki

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Re: Vibration under load

firecapt13 said:
It dosent really change with trim up or down or turning
Click to expand...

try a different prop then... borrow one from someone if you can, just to be positive before buying..
then again some places allow you to try a couple props before you buy em...
 
F

firecapt13

Seaman
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Mar 13, 2010
Messages
57
Re: Vibration under load

If it was u joints would there also be a noise. This thing is quiet while running except vibration.

for a 1992 alpha 1 gen II 4.3 what would be a good pitch and diameter prop. Boat is an 19 ft Wellcraft bowrider. It is used for cruising and pulling kids on tube and knee board
 
cedarjunki

cedarjunki

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Re: Vibration under load

firecapt13 said:
If it was u joints would there also be a noise. This thing is quiet while running except vibration.

for a 1992 alpha 1 gen II 4.3 what would be a good pitch and diameter prop. Boat is an 19 ft Wellcraft bowrider. It is used for cruising and pulling kids on tube and knee board
Click to expand...

you said there is no change when turning or trimming so the u-joints are pretty much ruled out......

as for the prop pull it off and see if there are numbers on it to go from.
 
180shabah

180shabah

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Re: Vibration under load

firecapt13 said:
for a 1992 alpha 1 gen II 4.3 what would be a good pitch and diameter prop. Boat is an 19 ft Wellcraft bowrider. It is used for cruising and pulling kids on tube and knee board
Click to expand...

It's not that simple.

We need to baseline what you have, then determine what if anything about it's performance you would like to change.

DO NOT rev your engine to 4k in neutral if you want it to stay together.
 
D

daydreamer1252

Petty Officer 1st Class
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Aug 7, 2007
Messages
212
Re: Vibration under load

Not a high time marine technician but....

Are we certain this is not an engine misfire that shows up under load??

Just asking........
 
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BRG25

Chief Petty Officer
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Jul 13, 2001
Messages
528
Re: Vibration under load

firecapt13 said:
for a 1992 alpha 1 gen II 4.3 what would be a good pitch and diameter prop. Boat is an 19 ft Wellcraft bowrider. It is used for cruising and pulling kids on tube and knee board
Click to expand...

My 19' Stingray with 4.3 came stock with a 14 x 23 (3 blade aluminum). Not sure how heavy your boat is but I would think that would be in the ball bark. What is the diameter/pitch of your current prop?
 
180shabah

180shabah

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Messages
4,995
Re: Vibration under load

daydreamer1252 said:
Not a high time marine technician but....

Are we certain this is not an engine misfire that shows up under load??

Just asking........
Click to expand...

We're not certain of anything yet...;)

BRG25 said:
My 19' Stingray with 4.3 came stock with a 14 x 23 (3 blade aluminum). Not sure how heavy your boat is but I would think that would be in the ball bark. What is the diameter/pitch of your current prop?
Click to expand...

Don't tease him, your stingray is lighter and faster than most hulls, I really doubt he could swing a 23 and be happy.
 
F

firecapt13

Seaman
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Mar 13, 2010
Messages
57
Re: Vibration under load

Ok went today to get prop. What is the difference in a prop with hub as unit and one that you have to buy hub assembly seperate. Advantages or disadvantages to either.

Took boat out again tonight to further check vibration and noise. Vibration was constant no matter the trim or turning. The only thing I felt in the steering felt like a car does when it is low on ps fluid.

Heard another noise near back of motor both running on lake and at idle. It sounded like a clunk or clacking. I am assuming it to be the exhaust flappers.

As for vibration is there a chance it could be engine coupler. It looked fine to me but I have never seen one.

I am nervous because this is my first boat and i rebuilt motor from cracked block and I want everything to be right with it.

Thank you to everyone that helps on this board.
 
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