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Old 07-11-2009, 05:42 PM   #1
MJM
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Thumbs up Alpha One Outdrive Vibration

Boat has been running perfectly, no issues.

Until today.

I'm getting a pretty strong vibration in the lower unit on occasion. It hasn't happened enough to know for sure exactly when, but it has happened when at very low throttle and turning sharply, as well as when in neutral at the dock with the lower unit all the way up. Under way seems to be fine.

Any thoughts? Any hints for things I should look at / try?

Thanks in advance!
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Old 07-11-2009, 06:44 PM   #2
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[QUOTE=MJM;99491]Boat has been running perfectly, no issues.

Until today.

I'm getting a pretty strong vibration in the lower unit on occasion. It hasn't happened enough to know for sure exactly when, but it has happened when at very low throttle and turning sharply, as well as when in neutral at the dock with the lower unit all the way up. Under way seems to be fine.


It sounds like your U joints are going bad. FYI you should NEVER run the engine with the outdrive "ALL THE WAY UP" This is a sure fire way to ruin the U joints and possibly have them lock up and explode. The all the way up position is also called "trailer" and it should only be used when the engine is off.

I'd bring the boat to a good marine mechanic and have them pull the drive and check/replace the U joints
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Old 07-11-2009, 06:54 PM   #3
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MJM, by all the way up do you mean full trim and not trailer? If so, your problem may be the prop. Minor, and I mean Minor, damage to one or all of the blades can cause the vibrations you speak of. If it is an aluminum prop, it will have enough flex to even out at speed. Hard turns and idle speed are where these imperfections will translate to the wheel. Just my two cents.
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Old 07-11-2009, 10:42 PM   #4
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NEVER run and I/O (inboard/outboard) {outdrive equipted} boat with the drive tilted all the way up!!!! running it for 3 minutes can do some damage to the drivetrain.

I got my money bet on bad/worn out u-joints. the u-joints are constantly spinning because they are directly connected to the rear of the engine via engine coupler. when the engine runs, the u-joints spin due to the flywheel spinning (where the engine coupler is bolted to).

you say the the outdrive is making vibration noises when tilted and when making turns. that is due to the u-joints are being flexed and binding when making turns or tilting/trimming the drive. your best bet to have the problem fixed is to take the boat to a marina/boat service person to have the u-joints replaced. also when it is being fixed get the gimbal bearing greased along with the transom, and have the engine alignment checked.

im not sure where you are located so i cant recommend a service location near you.

hope that helps, jst_4_kiks
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Old 07-12-2009, 06:58 AM   #5
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U joint would be my guess too.

Below is what Mercruiser has to say about running in "Trailer" mode. It is pasted right out of the operators manual.

"Power Trim allows the operator to adjust the drive angle, while
underway, to provide the ideal boat angle for varying load and water
conditions. Also, the Power Trim system “Trailering” feature allows
the operator to raise and lower the drive unit for trailering, beaching,
launching and low speed (below 1200 rpm engine speed), shallow
water operation.

CAUTION

Never trim the drive unit UP/OUT using TRAILER switch while
boat is underway at engine speeds above 1200 rpm. Use extreme
caution when operating with drive unit raised. Severe
damage to the drive unit may result if unit is raised beyond the
gimbal ring support flanges at engine speeds above 1200 rpm."
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Old 07-12-2009, 12:06 PM   #6
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Thanks to all for the feedback. VERY much appreciated.

The comment about it happening when fully up was more of a 'diagnosis' attempt - I was trying multiple scenarios to try to get the vibration to happen again so I could have a reasonable description for all you knowledgable folks as well as our mechanic.

Aside from the occasional (OK, semi-frequent ) forgetting to lower it before starting the engine and having to do it right then, we wouldn't run it with the lower unit "trailered".

I will post the results - thanks again everyone!
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Old 07-12-2009, 06:24 PM   #7
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Most everyone seems to be going for the U-Joints...so I am going to suggest the Gimbal Bearing instead. Either way, you have to remove the drive to check either one. The check is pretty simple once the drive is off. 10 minutes to remove an Alpha I. BTW: It takes quite a bit more time to put it back on.

A bad Gimbal Bearing will "FEEL Grumbly/Rough"..(Not Satin Smooth and slightly tight as it should) when you put two or three fingers in the bearing bore and roll the bearing back and forth. Your hands will get greasy doing this.

Bad U-Joints will feel Sloppy/Loose/Clunky.. when rocked back and forth.

Either way the drive has to be removed to do the check.
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