Mercrusier wobble

[Chadomosis]

So, this is my first experience with a stern drive motor. I got this thing running yesterday after god knows how long. The guy I got it from said 6 years but who knows. He had all the plug wires in the completely wrong places so I was skeptic that he had any idea what he was talking about anyway. The motor runs relatively smooth but when I increased the rpm, there is a pronounced wobble at the rear of the motor. My guess would be maybe an alignment issue, or a bad bearing? I did go through and check that everything is nice and tight, but maybe I missed something. All of you super-knowledgable stern drive types have a suggestion on what I should be looking for?

 

[wahlejim]

I would pull the outdrive and inspect the gimball bearing and ujoints. Open the inspection plate up on top of the outdrive and check the gears for any defects. Drain the gear oil from the stearn drive and check for metal shavings. All of this might take 30 minutes and a new gasket set.

 

[Chadomosis]

Great thanks. I'll check it out and see what I find.

 

[Jmunk]

Not sure what engine, but it's not unheard of for a engine mount to collapse. A bad u-joint would be a likely cause as well.

 

[alldodge]

With the wobble happening above idle I would start with the prop and the prop shaft.

Remove the prop and see what kind of play you have, a bit in/out is OK, no side to side. Place a straight edge next to the prop shaft and rotate to see if its straight.


Put the prop on a table and check to see that all blades are the same height, and that the hub is centered and intact. Next put muffs on and start the motor, then put in gear and rev slightly watching the prop.

 

[muskyfins]

If it's on the hard, is the drive down? How far down?

My first guess would be U-joint. Second would be coupler. Third would be alignment.

 

[Chadomosis]

It's a 3.0L Alpha one drive. The drive was down a little but probably not as much as it should be. I wasn't aware that it needed to be down, so I'm probably getting some fight from the u-joint. I'll start there.

 

[Bondo]

The motor runs relatively smooth but when I increased the rpm, there is a pronounced wobble at the rear of the motor.

Ayuh,.... Define Wobble,..??

What's Wobblin', Where,..??

 

[bajaunderground]

Check power steering pump as well...I had a harmonic shake first time out this year from a lack of power steering fluid. Filled it up, shake went away.

 

[harleyman1975]

Yes when you start out you put drive all the way down. when you go to plane out you put throttle all the way to full and then once boat is on plane you can start to back off to around 3300-3500. then you will want to trim the motor up a little bit (on my boat it is about 1/2 on the gauge) trim up too much and you will hear the motor start ot over-rev and the boat will loose speed. Just put it back down until it gets a bite again and your close to where you want to be. The sweet spot will change with load, speed and sea conditions. it will take time to find your boats sweet spot and where it runs the most efficiently.

 

[Chadomosis]

Didn't get a chance to mess with anything last night, but to respond to Bondo, at idle, it's as smooth as butter on hot bread. It's the increase in rpm's that the whole damned motor shakes like a wheel that's out of balance. Hard to tell where the problem is yet. I'm asking for the most probable spots to look for a behavior like that.

 

[muskyfins]

But it's still on the trailer?

You said wobble at the rear. Entire motor shake is different. Does it run smooth but shake? Or does it also run rough at elevated rpm's? If it's running smooth but entire motor shakes, I'd look for motor mount issue or harmonic problem on the front of the motor. (balancer, PS pump, loose pulleys, etc)

 

[Chadomosis]

It is on the trailer. I'll do some inspecting further and let you all know.

 

[Rick Stephens]

Drop the drive down as far as you can while running on muffs. This takes a lot of the pressure off the CVJoint.

In the end, you may need to remove the drive, insert a cut off water hose into the bell housing water passage and run the motor by itself to determine if the motor or the outdrive is causing the problem. Note, the driveshaft, CVJoint and gear train all turn in the outdrive when the motor is running. When the drive is out of gear only the propeller shaft itself is not turning.


Also important is make for sure and certain that the drive is full of lubricant!

Rick

 

[Chadomosis]

Yea, I read about the drive needing to be down after the fact. I should get some time tonight to take a better look based on all of the info that you all have given me. Thanks! I sure appreciate it!

 

[Chadomosis]

Ok y'all. Figured it out. The harmonic balance pulley had a nice gouge out of it. Looks like a half-butt mechanic was going to town trying to get it off of there. Anyway, that's the source of the wobble. Again, thanks for the guidance! Glad I stumbled onto this forum... You guys are alright!

 

[muskyfins]

Glad you found it out, but how can you be so sure? Was it that obvious? What did you observe? Did you replace it yet?

You know these forums.......pictures??

 

[Chadomosis]

Good point. It's pretty glaring, so I know it's an issue that needs to be resolved. I don't know if it will completely take care of the issue, but yea, I'm pretty sure that's the problem. Every time I try to upload a pic from my work pc, I get some errors. I'll post something from home so you can see what I see.

 

[Rick Stephens]

If you are direct loading pictures they need to be resized under 700k

 

[Chadomosis]

Got it. I think the IT dept here has some restrictions here for uploading stuff.