vibration in the boat @3000~4000Rpms

[Paange]

I recently purchased a used boat and it had a 150 hp mercury on it.It run well but it has a vibration during acceleration,after its on plane and i trottle back the vibration settles down but is still there. I inspected the prop, thinking it had something to do with that system and found that the prop shaft was good and tight but the prop itself had a wobble,not at the base but at the end that has a rubble gromet to hold it on the shaft. It lookes like this rubber should extend into the prop but it doesn't. I didn't notice that the prop would not move forwards and back but the rubber on the gromet did not extend into the prop itself. Any suggestion or advice would be appreciated Thanks Daryl

 

[Bondo]

Re: vibration in the boat @3000~4000Rpms

Ayuh,.... Welcome Aboard,.... Got any Pictures,..??

 

[Texasmark]

Re: vibration in the boat @3000~4000Rpms

Expect the prop and the propshaft (as a unit) to move back and forth (front to rear) slightly. This is the space the overrun clutch in the lower unit needs to function.

ANY lateral (vertical in this case) variance in your prop is a no-no measured: Easiest and most non scientific way to find the answer to that question is to get out on a concrete (Hard-immovable) surface and set the engine vertical preferably, putting the prop shaft parallel to the hard surface.

Get a gauge of some sort, doesn't matter what it is, just something that you can put between the prop hub, shaft, blade tips, and whatever else you feel like measuring and the ramp/driveway/whatever, and rotate the prop by hand while watching the gap between the gauge and the part of the prop you are measuring. If you have ANY noticeable variance in the size of the gap as you rotate the prop either get a new prop or take yours to a prop shop to have it repaired.

Mark

 

[Paange]

Re: vibration in the boat @3000~4000Rpms

Expect the prop and the propshaft (as a unit) to move back and forth (front to rear) slightly. This is the space the overrun clutch in the lower unit needs to function.

ANY lateral (vertical in this case) variance in your prop is a no-no measured: Easiest and most non scientific way to find the answer to that question is to get out on a concrete (Hard-immovable) surface and set the engine vertical preferably, putting the prop shaft parallel to the hard surface.

Get a gauge of some sort, doesn't matter what it is, just something that you can put between the prop hub, shaft, blade tips, and whatever else you feel like measuring and the ramp/driveway/whatever, and rotate the prop by hand while watching the gap between the gauge and the part of the prop you are measuring. If you have ANY noticeable variance in the size of the gap as you rotate the prop either get a new prop or take yours to a prop shop to have it repaired.

Mark

Thanks for the help I'm not home this week but will check it out when I get home I can tell you that it doesn't seem to have much end play, "term in my industry" left to right, but it has a lot of up and down movement at the open end of the prop ,at the drive end it seems tight , another thing someone mentioned is that stainless props are not forgiving and if i should hit something with it it's more apt to break something in the drive where as alum props will bend or chip not damaging the out drive. is there any truth to the statement? Thanks again Daryl

 

[Bondo]

Re: vibration in the boat @3000~4000Rpms

Thanks for the help I'm not home this week but will check it out when I get home I can tell you that it doesn't seem to have much end play, "term in my industry" left to right, but it has a lot of up and down movement at the open end of the prop ,at the drive end it seems tight , another thing someone mentioned is that stainless props are not forgiving and if i should hit something with it it's more apt to break something in the drive where as alum props will bend or chip not damaging the out drive. is there any truth to the statement? Thanks again Daryl

Ayuh,... Some truth to it, but there's always the possibility of internal damage, even with an aluminum wheel...

 

[Maclin]

Re: vibration in the boat @3000~4000Rpms

You will need to remove the prop and see if the up and down you see now at the open end of the prop is due to the prop shaft being bent. Even though the shaft is "tight" at the end where it exits the drive it can have been bent by a prop strike and the "free" end be moving around in small circles as it turns (up and down if viewed just from the side).

 

[Texasmark]

Re: vibration in the boat @3000~4000Rpms

You will need to remove the prop and see if the up and down you see now at the open end of the prop is due to the prop shaft being bent. Even though the shaft is "tight" at the end where it exits the drive it can have been bent by a prop strike and the "free" end be moving around in small circles as it turns (up and down if viewed just from the side).

Mr. P.

Since you already know that you have damage, then this would determine whether or not it is the prop or the shaft, or both. My experience is that the prop will go before the shaft, but not necessarily.

So, pull the prop and rotate the shaft by hand while using a home made gauge to measure for any out of round. If the shaft is out of round then the question would be by how much and then another question would be is it sufficient to do any damage.

On SS vs Alum there is truth to what you said. However, I had a 125 Johnson back in '72 and I could be just at idle in a bunch of 1" saplings and ding my alum prop. Got tired of it and put on their new at the time SST, Teflon coated SS and never had another problem with a prop, course I didn't smash it into any rocks either.....all bets for either prop are off in that event......but today they have depth finders that can warn you of obstructions when you are "learning" new water.

Mark

 

[Paange]

Re: vibration in the boat @3000~4000Rpms

Mr. P.

Since you already know that you have damage, then this would determine whether or not it is the prop or the shaft, or both. My experience is that the prop will go before the shaft, but not necessarily.

So, pull the prop and rotate the shaft by hand while using a home made gauge to measure for any out of round. If the shaft is out of round then the question would be by how much and then another question would be is it sufficient to do any damage.

On SS vs Alum there is truth to what you said. However, I had a 125 Johnson back in '72 and I could be just at idle in a bunch of 1" saplings and ding my alum prop. Got tired of it and put on their new at the time SST, Teflon coated SS and never had another problem with a prop, course I didn't smash it into any rocks either.....all bets for either prop are off in that event......but today they have depth finders that can warn you of obstructions when you are "learning" new water.

Mark

I removed the prop and set up a 1in dial indicator on the spline just below the thread and measures .004 run out, it also had about 0.004 diflection when i pushed it ,but always came back to 0.00 when released ,I checked the in and out motion and it was .035 as you explained. what I did notice was the spline that is inserted into the prop had what I would consider too much side movement or slop as it set in the adapter that is inserted into the prop,could this be the sorce of the vibration,I would say that the side play in that piece was above .080 in,do they sell new parts for the inside of the prop or should it be sent out for rebuild? your help is greatly appreciated if you ever get into this area I owe you a fishing trip

 

[Texasmark]

Re: vibration in the boat @3000~4000Rpms

I removed the prop and set up a 1in dial indicator on the spline just below the thread and measures .004 run out, it also had about 0.004 diflection when i pushed it ,but always came back to 0.00 when released ,I checked the in and out motion and it was .035 as you explained. what I did notice was the spline that is inserted into the prop had what I would consider too much side movement or slop as it set in the adapter that is inserted into the prop,could this be the sorce of the vibration,I would say that the side play in that piece was above .080 in,do they sell new parts for the inside of the prop or should it be sent out for rebuild? your help is greatly appreciated if you ever get into this area I owe you a fishing trip

This forum sells a lot of props (iboats, that's why the forum is here....to make money.) For the cost of fooling around with a prop shop and all the stuff you can buy a brand new prop of your choice and be done with it. The numbers you mentioned in runout that you measured with your dial cal. I guarantee you are not the source of your problem. Get a new prop Sir!

Mark