Odd Vibration has me baffled

[haugy]

Took the boat out last weekend, ran around with just me fine. Got what felt like a minor vibration at about 3200-3500 rpm. Very minor and hard to notice.

Put the family in the boat for a total of about an additional 400lbs of women, kids, grandma, etc. Once I got it above 2800-3000 rpm on plane it would start to shake real bad. Not in the wheel, just an overall vibration in the boat. I figured it's a prop problem. Prop looks perfect.

Plus I took it out yesterday alone, and it ran fine. Again a slight vibration at 3200 rpm. But barely noticeable.

So something is off, prop, shaft, what? What would cause the vibration to get worse as the boat was working harder with a load? I checked the engine mounts and they are solid and holding.

Any ideas? My guess is the shaft or something in the driveline is out of whack.

[Zim]

Any slop in the steering? Play in the rudder?

[haugy]

Nope, steering is tight and smooth. No vibration or shaking when underway.

[jzelt]

I know when I hit our prop, it was about the same issue you state, refurbished the prop and that reduced it, new prop resolved it.

Shaft secured to the drive(don't know if it is v-drive or direct, but should be same).

Have some seaweed/grass on the prop? Quick burst in reverse would possibly clear it off.
I believe it has to be drive issue as well as you.

[lively]

http://youtu.be/3_w0LvD6gEc

Everytime you have vibration

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[Cusefan78]

My guess is the prop or the the driveshaft. Unhook the prop shaft and check to make sure it's square with the engine. While your down there check to make sure all the mounts are tight. Good luck

[NoWake]

My experience with vibration was bad. I ended up with a shaft failure just behind the strut at the beginning of my key way. I only wished I had taken the prop off and gave it a look over. Worse yet I had read a couple months earlier about a shaft failure on here. I ended up losing the prop and had to replace both. I still stew to this day about it! 91 comp research shaft failure here. Initially I though I was hallucinating the vibration, didn't feel it in the wheel, but noted it more through the pylon.
Good luck Haugy

[Hagman]

I had a similar vibration @ 1200 hrs. It was a worn shaft barring . If the prop was perfect the vibration would almost go away.

[92SupraComp]

Check the end of the shaft. Same here. My prop shaft cracked underneath the prop! Luckily it didn't break off, but cracked all the way through and almost all the way around. The end of my prop shaft was 1/4" out of circle.

[haugy]

Yeah, I'm going to pull the shaft, yay. Hopefully nothing bad.

[chris young]

I know I sound like a broken record (funny, some people on this site wouldn't know what a broken record sounds like :p) but this is for anyone else reading the thread. If you have the shaft out, now's the time to lap that prop, and even if you don't see a crack, 50 bucks buys a dye penetrant kit to properly check for cracks you may not see. Pretty cheap peace of mind if you ask me. Also you'll probably need to replace your shaft coupler unless it's the clamp or tapered type.

BTW if you don't have a lathe, the way I lapped my prop (worked so well I went too deep so be careful) rig up something to bolt to the coupler that you can chuck in a drill. I was lapping by had and not getting anywhere, then I just put a bar with two holes in it, and a bolt in the centre, bolted to the coupler, and then just put the prop on the floor and had at it. Be careful and go slow with easy pressure, works like a charm.

[haugy]

Chris, yeah if my shaft comes back straight and crackless I'm getting an ACME prop. Plus I'm going to check the strut. See if that cleans up the vibration.

Yep, can't overthink the lapping. I always just put it on a rollers like you'd get for long pieces of steel projects. Then I put a bolt on the shaft, large nut, and drill. Done. One friend turns the drill at slow speed, I hold the prop..