Faint vibration but I can make it stop... until next time???

[KSalibs]

Hey guys,

hope everyone is keeping there sanity through the winter months... this sight always helps ease the pain of the winter months...

I had this really odd issue at the end of the season last year.. so id pull off the dock and immediately once the boat was at 800, 1000 ish rpms there would be a very suddle vibration that i would feel from the starboard side. if you weren't used to running the boat i bet you wouldn't notice... actually... if you brought the port up on its own then brought the starboard up you would deff feel the difference.

so her is the strange part... on the way out the lagoon i thought maybe there was something stuck on the prop (like debree) so I put it in reverse a few times back and forth and poof... gone... the next outing i head out same thing. every trip out for the rest of the season... which was 3 trips including the haul out.

i cant for the life of me figure out what this could be... unless there is really something getting hung up on the prop but i highly doubt it... after pulling it i saw now scoring or hull scuff... out side of inspecting visually i did pull on the props back and forth and felt a slight amount of play in the shaft about a a 32nd forward and aft... felt next to nothing side to side, up and down... I want to say that the port had the same amount of play as the starboard...

I figured i would have the alignment done and the engine mounts checked out before i drop it in next year but im still not sure what putting it in revers could do to actually make a vibration go away... any force that the revers would have caused would immediately be undone as soon as the boat was brought on plain...

any suggestions are appreciated! FYI i did bump very slightly at idle mid season checking out a lagoon we are hopping to buy property on.. no visual damage to props... no immediate vibration as a result... props are going out for conditioning just incase..

boat is a 2003 320 DA with inboards 6.2 ZF 400hrs...

thanks again!!

 

[TNT8808]

I had a similar condition when we purchased our boat. I put up with it for a few outings, and then had the boat hauled out. Everything was tight, and no visual damage whatsoever. Sent the props out to be Prop-scanned, and all 8 blades needed a little fine tuning but 1 of them was out 1-1/2".

 

[KSalibs]

Thanks. I posted on sea ray face book group and was given the following recomendations.

Check:
the cutlass bearing set screws
the coupler bolt could be loose
the props should be scanned.
the engine mounts should be checked
the alignment should be done.

Let me know if you guys know of anything els. thank you!

 

[fwebster]

Scanning the props would be my last resort here just because the vibration clears at a fast idle. A prop out of balance or bent will get worse not improve as rpms increase. For that matter the Facebook answers fit in the same box: Loose coupler bolts would cause the vibration to be horrible at higher rpms; serious alignment issues cause the prop shaft to whip as rpms increase, again a horrible shake at high rpms; engine mounts that are loose allow the engine to move about and would vibrate at all rpms.

Have you ever replaced your plug wires? Mercruiser plug wires are known to break down over time so they should be replaced whenever you do a tune-up. A miss or weak spark on one cylinder will be obvious at low speed but will seem to clear as rpms increase. Similarly, a bad or dirty injector will seem like a miss at low speeds but not be noticeable at high rpms. A low speed miss will feel like a vibration but will not be apparent as rpms increase. You won't feel or be able to measure the miss above about 1000-1200 rpms, other than a loss in efficiency or top end speed.

 

[mquiet]

Frank, I think I disagree with you. I touched the bottom in the ICW and I notice a very slight vibration in a narrow RPM range as I bring it up and then it disappears. My diver told me the following month that he noticed a n ever slight nick in my stdb prop. So my guess was that was causing vibration. Due to the size when RPM increases the high rate of flow over the props creates a slight gap between water and prop which is similar to a laminar flow over a prop on an aircraft or wing. It might not be his issue but could a slight tweak in the prop simulate this? Thanks for hearing my thoughts on this. Not saying I am right just wondering what others think.


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[KSalibs]

Scanning the props would be my last resort here just because the vibration clears at a fast idle. A prop out of balance or bent will get worse not improve as rpms increase. For that matter the Facebook answers fit in the same box: Loose coupler bolts would cause the vibration to be horrible at higher rpms; serious alignment issues cause the prop shaft to whip as rpms increase, again a horrible shake at high rpms; engine mounts that are loose allow the engine to move about and would vibrate at all rpms.

Have you ever replaced your plug wires? Mercruiser plug wires are known to break down over time so they should be replaced whenever you do a tune-up. A miss or weak spark on one cylinder will be obvious at low speed but will seem to clear as rpms increase. Similarly, a bad or dirty injector will seem like a miss at low speeds but not be noticeable at high rpms. A low speed miss will feel like a vibration but will not be apparent as rpms increase. You won't feel or be able to measure the miss above about 1000-1200 rpms, other than a loss in efficiency or top end speed.

Thank you Frank I did actually have an issue with the same motor where the RPM's would be low at iddle. I had actually had the motor stall on me once or twice while pulling off the dock id i font let it warm up for a little while.

in order for the motor to hold a solid idle i would have to bring the throttle up just a hair so it would idle at the right RPM.

the cables are the same onse that were on the boat when i got it however i have no idea how long they have been on the boat prior to that... i changed the plugs when i bought the boat. which was 2 seasons approximately 150 hours ago...

with this information would you say that the cables could be suspect still.

I appreciate this information i would have never thought this to be the issue but it does make sense. I will obviously check everything else as well.

 

[fwebster]

Definitely suspect since you haven't changed the plug wires and don't know if or when they have been changed.

Mercruiser continues to improve their wires so I would buy from a high volume dealer or online source so you get the newest available and sets that have not been laying on a shelf somewhere for years.

 

[spikedaddy99]

I kicked off a plug early last season and had this issue. I couldn't idle until warm without bumping throttle to about 800rpm. At the time I assumed IAC and changed them, but obviously that didn't work. Then I found the loose plug...Fixed.

 

[KSalibs]

Great info gents! Thank you!!!


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[KSalibs]

If I changed the plugs 140 hours 2 seasons ago do I need change them as well or should they be good?


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