Vibration at low speed

[Smokey988]

I have had a vibration on the new style Alpha one Gen 2 since I purchased it used a few years back. U-Joints and gimbal bearing are new.
The vibration only appears in the water between 5-10MPH but is annoying. Above that speed no vibration is felt. I checked the propeller shaft and it looks to have between 5-7 thou of deflection.

Over the years I have had 3 or 4 propellers and all are exactly the same. At the speed when the vibration occurs I swear I can feel it in the steering wheel.

Am I looking at coupler or the propeller shaft as the culprit? My thought is the coupler would vibrate even when not in gear at that certain rpm.

 

[j cat]

did you grease the u joints every year in the fall to set it up in the winter ?
inspect the lower unit ..inspect the lower unit top cap to see if water had oil in the out drive ..

 

[Scott Danforth]

do you pull the drive every year, inspect the gimbal, u-joints and alignment?

 

[achris]

I have had a vibration on the new style Alpha one Gen 2 since I purchased it used a few years back. U-Joints and gimbal bearing are new.
The vibration only appears in the water between 5-10MPH but is annoying. Above that speed no vibration is felt. I checked the propeller shaft and it looks to have between 5-7 thou of deflection.

Over the years I have had 3 or 4 propellers and all are exactly the same. At the speed when the vibration occurs I swear I can feel it in the steering wheel.

Am I looking at coupler or the propeller shaft as the culprit? My thought is the coupler would vibrate even when not in gear at that certain rpm.

Need to know what engine (model, year, serial number). Some engines have an inherent vibration in the 1700-2200 rpm range... (which is exactly the sort of speed you're referring to)

Chris.........

 

[Smokey988]

do you pull the drive every year, inspect the gimbal, u-joints and alignment?

yes. I pull driver every year and use alignment bar. Last year I pulled drive and replaced gimbal bearing and u-joints. All last summer same thing with the annoying vibration at slow speed coming in and out of no wake zone.

Last fall took drive off again, replaced u-joints again, gimbal bearing, u-joint shaft, yokes, new bearings and set the rolling torque correctly with dial indicator torque wrench.

The alignment bar goes in and out with one finger and grease marks look good.

Took boat out on the water last week and same low speed vibration.

Back to the drawing board. When I measure the tolerance on the prop shaft I have about .13mm which works out to 5.11811 thou. Manual says over 7 thou is considered bent.

I figured for sure it was going to be the upper bearings in the drive housing as they were not smooth when I pulled them out.

 

[Smokey988]

Need to know what engine (model, year, serial number). Some engines have an inherent vibration in the 1700-2200 rpm range... (which is exactly the sort of speed you're referring to)

Chris.........

Hey Chris,

First let me thank you for all the videos and information you have posted over the years. It has certainly helped me a ton. So Thank You

The motor is a 2007 4.3MPI 220HP serial # 0W670363.

 

[Scott06]

yes. I pull driver every year and use alignment bar. Last year I pulled drive and replaced gimbal bearing and u-joints. All last summer same thing with the annoying vibration at slow speed coming in and out of no wake zone.

Last fall took drive off again, replaced u-joints again, gimbal bearing, u-joint shaft, yokes, new bearings and set the rolling torque correctly with dial indicator torque wrench.

The alignment bar goes in and out with one finger and grease marks look good.

Took boat out on the water last week and same low speed vibration.

Back to the drawing board. When I measure the tolerance on the prop shaft I have about .13mm which works out to 5.11811 thou. Manual says over 7 thou is considered bent.

I figured for sure it was going to be the upper bearings in the drive housing as they were not smooth when I pulled them out.

I know you said you tried several props, but were any of them balanced? I had a similar issue had the prop balanced at a repair shop and issue went away. Was fine at high speed but I must have bent it at some point kissing bottom

 

[Smokey988]

I know you said you tried several props, but were any of them balanced? I had a similar issue had the prop balanced at a repair shop and issue went away. Was fine at high speed but I must have bent it at some point kissing bottom

Originally it came with the mercury prop and a Apollo stainless prop, and I now have 2 new aluminun props. All are exactly the same result so I am thinking not propeller.

 

[achris]

...
The motor is a 2007 4.3MPI 220HP serial # 0W670363.

Yep (I suspected). As you see by my signature I have the same engine. Mine does a similar thing at the same engine speed, as did my 1994 4.3LX. They are a 90 degree V6, and that's an inherently unbalanced configuration, and it's most noticeable under load, almost gone completely when not under load. GM even put a Balance Shaft in to try to alleviate the problem, but it's still there. Next time you're out lift the engine cover and watch the engine. It'll be going up and down slightly at that speed. That's your vibration.... There is no cure....

Chris...

 

[kenny nunez]

I had a few OMC customers with the early version that did not have the balance shaft. It felt like the engine was having a misfire.

 

[Smokey988]

Yep (I suspected). As you see by my signature I have the same engine. Mine does a similar thing at the same engine speed, as did my 1994 4.3LX. They are a 90 degree V6, and that's an inherently unbalanced configuration, and it's most noticeable under load, almost gone completely when not under load. GM even put a Balance Shaft in to try to alleviate the problem, but it's still there. Next time you're out lift the engine cover and watch the engine. It'll be going up and down slightly at that speed. That's your vibration.... There is no cure....

Chris...

Thanks Chris.

 

[nola mike]

Yep (I suspected). As you see by my signature I have the same engine. Mine does a similar thing at the same engine speed, as did my 1994 4.3LX. They are a 90 degree V6, and that's an inherently unbalanced configuration, and it's most noticeable under load, almost gone completely when not under load. GM even put a Balance Shaft in to try to alleviate the problem, but it's still there. Next time you're out lift the engine cover and watch the engine. It'll be going up and down slightly at that speed. That's your vibration.... There is no cure....

Chris...

Interesting. Noticed the same thing on mine as well, didn't think it would be an issue with the balance shaft.

 

[achris]

Interesting. Noticed the same thing on mine as well, didn't think it would be an issue with the balance shaft.

It's not an issue with the balance shaft, it's why the balance shaft is there. On the engines before the balance shaft, Merc used fluid mounts to try to reduce the vibration..

Chris...

 

[nola mike]

GM even put a Balance Shaft in to try to alleviate the problem, but it's still there.

It's not an issue with the balance shaft, it's why the balance shaft is there. On the engines before the balance shaft, Merc used fluid mounts to try to reduce the vibration..

Chris...

Well, I'm just going to assume that's how it is

I've been chasing u-joints, gimbals, couplers since I installed the engine (though since all checked out I gave up. 500 rpm of slight vibration still better than the 4600 rpm of vibration with the old setup.

 

[QBhoy]

Hey Chris,

First let me thank you for all the videos and information you have posted over the years. It has certainly helped me a ton. So Thank You

The motor is a 2007 4.3MPI 220HP serial # 0W670363.

Don’t suppose the balancer shaft and wheel is loose ?

 

[Rick Stephens]

It's not an issue with the balance shaft, it's why the balance shaft is there. On the engines before the balance shaft, Merc used fluid mounts to try to reduce the vibration..

Chris...

So even with a balance shaft the motor wriggles around? Yuck.
(My morphodite 4.3 has no balance shaft)

What happens if you add fluid mounts to that setup?

 

[achris]

So even with a balance shaft the motor wriggles around? Yuck.
(My morphodite 4.3 has no balance shaft)

It's not that bad. If you're aware of it, you can detect it.

What happens if you add fluid mounts to that setup?

Don't know, never tried that...

Chris...

 

[QBhoy]

Any pics of the prop ? Presumably the thrust washer is in place ? What prop you have on her ?
What rpm is she at when this happens

 

[nola mike]

What happens if you add fluid mounts to that setup?

You don't want to know. Bad, bad things according to @Scott Danforth when I suggested that it might just make for a suuupper smooth luxo ride.

 

[QBhoy]

It could be other things too. More thinking around engine causing it. Bad fuel, water getting in from frost damage or the famous diz cap failing.