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Vibration

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dutch-us View Drop Down
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    Posted: November-21-2022 at 2:05pm
I have a 1968 Mustang C/Craft with a POLY 318. When hard throttling to pull up a heavy skier, it vibrates terribly. Once cruising, not bad. I have aligned the propeller shaft and even installed mufflers. The engine runs great.

Any ideas?
68 Mustang Wes
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TRBenj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: November-21-2022 at 3:10pm
Junk prop or bent shaft are the 2 biggest sources of vibration.

Misalignment will dampen vibration, not exacerbate it.

How’s the strut bushing?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jonny Quest Quote  Post ReplyReply Direct Link To This Post Posted: November-21-2022 at 11:23pm
Tim hit the main ones:  1) bent shaft; 2) strut bearing; and 3) unbalanced / damaged propeller.

You can check for "play" of the shaft in the bearing by wiggling the prop side-to-side and verifying movement of the shaft in the strut.

How old is the prop? Has it been hit and "fixed"?  Maybe post a photo of the prop (include the hub).

You can measure for a bent shaft easy enough while the shaft is on the boat.  You need a dial indicator and then attach the base of the dial indicator onto the strut.  You want to check the shaft just aft of the strut.

Can you provide a bit more info on your shaft alignment?

JQ
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1994 Ski Nautique Open Bow (sold)
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dutch-us View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dutch-us Quote  Post ReplyReply Direct Link To This Post Posted: November-23-2022 at 9:48am
I replaced the prop with a one inch lower pitch, because most of what I do is idle or ski.

I haven't measured play for strut condition but the bearing looks good and shaft spins with ease.

I will measure for out of round but I would think the vibration would increase, with RPM, if it is bent.

The previous owner did stringer work and the mounts are now sitting on aluminum angle iron which I wonder about.

Are new isolators readily available?

Thanks,

68 Mustang Wes
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 63 Skier Quote  Post ReplyReply Direct Link To This Post Posted: November-23-2022 at 11:05am
I doubt isolation is the problem, or the fix.  Since you mention the vibration is at it's worst when under max load, engine/prop loaded up trying to pull up a heavy skier, I'm going to guess you will find a worn out strut bearing.  Could be wrong, but agree with above that it's strut or shaft or prop.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dutch-us Quote  Post ReplyReply Direct Link To This Post Posted: November-23-2022 at 6:13pm
Thank you all and it's time to fire up the garage furnace and go to work.
68 Mustang Wes
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