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strange vibration??

hac

hac

Member
I hardly even want to post with the way they all turn out lately but maybe some of the old school types will chime in with some insight to my dilema.

I have developed a vibration, somewhat harmonic. Seemed to come on slow and intermittent, now a little more constant.

Mostly obvious at headway and lower speed. Put in gear -O.K second or two later feel and hear vibration. Its slight but there.

checked the top and bottom of drive-all good
prop-good
swapped to new drive-no change (even seemed worse)
changed gimbal bearing- still there
u-joint- good
alignment- right on
motor mounts-seem fine

ran the boat this weekend to see if any change if it might get worse, nothing??
performance is excellent!

Any thoughts??
 
It sounds like you covered all the major stuff...

i wonder if it could be in your drive coupler???

you say you can hear it??.. like a humming or like a subwoofer at a real low note?? im just trying to come up with some sound comparisons for others to think about..
 
Im thinking drive coupler too. Mine was on the way to taking a crap last year. I lost speed and noticed more vibration/noise when turning or trimming. At the end of the season I had lost 4 mph, it would make noise at very low steering, trim angles. I foun out that that was the culprit when I pulled my motor and saw the rubber breaking out of the coupler. If you need a new one, use e-bay. They are very cheap and brand new off of there.
 
Hmmm. Drive coupler??

When it started it was more a feeling than a noise. A couple seconds after putting it in gear, you felt it right in the controller. Now that I notice it I hear it too. You know how these things are. Once you notice you lose track of "is it worse or just me??"

Overall performance at this time seems unnaffected.

Trim position and steering seem to have no effect toward the feel.
 
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might be a long shot here - but what about the harmonic balancer - i have seen those fail for no reason. it sounds like it is engine related, as changing the drive made no differance.
 
When you did all your work did you do a engine alignment. You would have had to insert a alignment bar through the gimbal when the drive was off. I have seen them make noise and create a vibration if alignment is out. also premature bearing failure. Just another thing to consider.
 
can you get it to do it free rev out of gear at the same RPMs ? like red said could be a balancer issue...just had a strange one myself...new GM gen VI marine engine, they put the wrong lower timing gear on at the factory, was supposed to have a reluctor wheel in front of that gear, but it did not...allowed balancer to go back to far, 1/8" past the end of the crank, in 100 hrs wobbled the balncer out to the point you can slide it on and off by hand !!! battling GM right now to see what they will do for their screw up !!!! good luck Rob
 
Sorry I guess what I was saying did you actually use an alignment bar? even if your drive shaft slips in does not mean alignment is right on. When using an alignment bar the bar could still go in tight and hard to spin. you then must adjust your engine so the bar turns free and easy. Or you could hear a low speed noise and feel a vibration, I believe It is worth checking again before you have to do major tear down.
 
thanks for your thoughts guys,

aligment tool - yes and double checked prior to re installing orig. drive

cannot recreate the problem if not in gear

i would expect premature bearing failure:eyecrazy: or balancer issues would be occurring in neutral as well
 
Longshot, Have you tried an aluminum prop as opposed to a stainless? (I assume you have a stainless prop). It may seem stupid but the weight of the stainless prop can cause noises and vibration. If it goes away with an aluminum, I would ignore it or change the pressed in hub if you have one.
 
Boy this is a hard one to crack, I like the Idea of trying a different prop. Bad prop will do it for sure if that's it, You sound pretty in tune with your boat, Did you torque your transom assay. bolts? Should be done before alignment. Is something loose and going undetected?

Sounds like you checked everything, may want to go around put a wrench on everything again.

Look at your harmonic balancer while running to see if it looks to be wobbling, another check is to pull #1 spark plug By hand bring the piston up to top dead center. Use a dial indicator if you have one, or a pencil will work in the cylinder hole to find true TDC. Then look at your timing marks they should be lined up at TDC if its off by a few degrees you have a spun balancer. If all checks out your balancer is good. I hope some of this may help its just where I would be going. If it is a balancer I sell hard core SFI 10,000 rpm race balancers, I use tem on everthing we build almost. They beat the hell out of any fluid dampner.


mkhammer
 
Hope to have a little more time this wkend to check some of what has been mentioned. Prop, balancer and loose anything.

Beyond that its time to turn it over to the marina. Its pretty much storage time anyway.:(

MK, too bad you weren't closer. I'd just drag it to you. Besides fixing the said problem, I've got an itch for some upgrades. The guys around here don't want to mess with performance upgrades and actually reccomend against them.
 
hac,I guess its the area in which we live in , Everyone out my way does performance upgrades on their performance Boats just about, Where I do alot of boating is Lake Havasu AZ. It's like a war there to see who is king of the lake, Basically who ever spends the most money wins. 140 MPH cats all over, Now I have seen a few MTI 44 super cat that run 170 MPH. There is always someone bigger and faster. So I got into performance upgrades, There are alot of sound dependable upgrades to do, Some guys stuff is so hyped out they have to rebuild every 50 hr and blow drives like crazy. Unless I'm racing this is not my ides of fun. I have fun in my convincor I beat most V-bottoms and alot of cats too. I work on alot of boats I have come to appreciate the quality of my convincor more and more and the looks are stunning,
I try to take a practical approach to performance, There are a lot of great upgrades that don't sacrifice your dependability when done right. When you are ready I can supply parts give me a shot at it. I will do my best to save you some dough.

mkhammer
 
Since you used a second drive and the issue still remains, we know what its not. Its not the drive.. So the next question would be. What remained the same when you swapped the drive? Same prop? same thrust washer? I'm assuming your a bravo set up and not a trs. Since it happens in gear and at low speeds (is this correct?) logically speaking we would look at the prop, gimbal brg. (for now i'm going to throw the engine coupler out of the equasion) the reason being, they ususally just go out and you quit moving all together. Other things that could be moving are motor mounts (sometimes hard to see if they are broke) What we can check here is if the mount bolt has dropped. Does the vibration get worse as you turn, what trim level is this at? Does it change as trim angel changes.
 
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