Bad Vibrations (from an alternator)

[spicemouse]

Hello again Canal World,

 

I've been on my boat for a while now and I'm slowly getting to understand all it's quirks. One I wasn't happy with was a certain vibration when the engine ran in an rmp range. Upon investigation it looks like I have a wobbly alternator, which is wobbling the whole engine mounting! I've had issues with the mounting, and it seems like this is the root cause. 

Engine is a late 90s Beta 43, and I think it's the starter alternator. I recorded it in action which really shows the wobble:

 

 

Any suggestions on how to alleviate this? Alternator too tight, too loose, just bad design?

Cheers,

 

David

[GUMPY]

I suspect that the bolt behind the alternator could be an engine mount bolt and the nut undeneath the plate is loose or the mount has deteriorated.

But I may be wrong.

Edited June 25, 2021 by Loddon

[spicemouse]

2 minutes ago, Loddon said:

I suspect that the bolt behind the alternator could be an engine mount bolt and the nut undeneath the plate is loose or the mount has deteriorated.

But I may be wrong.

It's mounted to the engine mounting. 

 

 

[OldGoat]

Coloud be exacerbated by an alternator controller trying to 'uip the amps' to the batteries and putting too large a load on the transmission.

I have  the same problem and swithch the controller off until either we get moving 'fast' to increase the engine speed OR until the initial high charge rate drops down a 'tad'....

[system 4-50]

The problem is due to the engine being painted red, not green.

[spicemouse]

7 minutes ago, system 4-50 said:

The problem is due to the engine being painted red, not green.

Red ones go faster

[Tony Brooks]

I don't like the deign of the extension the alternator seems to be bolted to. The only mount point to the actual engine seems a long way back from the alternator itself. The whole thing seems to flex along its length. Loddon also has a very good point.

 

Do you get maximum alternator output? I am wondering if you have a phase down.

[GUMPY]

To me in the video it looks like there is relative movement between where the arrows are on this pic.

This could mean that  where the mount is fixed to the engine it is loose.

I would check the engine mount to make sure its tight, then the bolts holding the mount onto the engine plus the bolt holding the bracket on at the back are tight. Dont forget the nut under the engine mount bracket when they are loose movement is exactly like that i.e. the engine rocks diagonally.

The bracket is moving in time with the engine rather that in time with the alternator. To get that much movement something must be loose.

[spicemouse]

6 minutes ago, Tony Brooks said:

I don't like the deign of the extension the alternator seems to be bolted to. The only mount point to the actual engine seems a long way back from the alternator itself. The whole thing seems to flex along its length. 

Yes, that does seem to be the case. The drive is hydraulic, so the engine only vibrates by itself. 

 

7 minutes ago, Loddon said:

 

This could mean that  where the mount is fixed to the engine it is loose.

 I can certainly check, but I had the engine remounted 2 months ago. The wear on the wooden mount looks consistent with this issue being around for a while (it was remounted due to the the split in the wood). 

 

10 minutes ago, Tony Brooks said:

Do you get maximum alternator output? I am wondering if you have a phase down.

I can stick my multi meter across it running, but I'm afraid I don't know what to expect for it being phased down. 

[Tony Brooks]

5 minutes ago, spicemouse said:

I can stick my multi meter across it running, but I'm afraid I don't know what to expect for it being phased down. 

 

Not unless it has a high amp clamp on it. Even with two phases it would produce  near regulated voltage.

 

If that square red steel bar is a Beta fitment, I would suggest there is a mounting bolt at the front end missing or loose.

[Tracy D'arth]

Is the swivel mount behind the alternator tight? Is it one of the single big lug mounts or the old 2 point mounting?

[spicemouse]

36 minutes ago, Tracy D'arth said:

Is the swivel mount behind the alternator tight? Is it one of the single big lug mounts or the old 2 point mounting?

 

 

All nuts nice and tight. 

Edited June 25, 2021 by spicemouse

[Tracy D'arth]

Looks like there is no way that the "bolt" is rigid in the mounting bracket on the engine. Is it welded in or just floating ?  Its a very odd fixing.

[Col_T]

Is this alternator original equipment? If not, that might explain why there appears to be 'free space' between the alternator mounting lugs and the mounting bracket on the engine, which is, I guess, just a different way of putting @Tracy D'arth's comment!

[spicemouse]

The whole thing is attached at a mounting arm which is bolted to the engine mounting. 

 

 

Regardless of the mounting, could the vibrations be coming from some issue in the alternator?

2 minutes ago, Col_T said:

Is this alternator original equipment?

I dunno! It's over 20 years old and I don't know if it was even new when fitted. Who knows who decided on this setup.. 

[Tracy D'arth]

Question.

 

The metal bar between the 2 mounting lugs on the alternator. Is it fixed, as in part of the mounting arm?

[spicemouse]

8 minutes ago, Tracy D'arth said:

Question.

 

The metal bar between the 2 mounting lugs on the alternator. Is it fixed, as in part of the mounting arm?

This bit?



I think I'd have to remove the alternator to be sure. Loosening everything till I can move the alternator doesn't allow it to rotate. Looks to me like it is a tube which passes through the lugs. 

2 hours ago, Loddon said:

This could mean that  where the mount is fixed to the engine it is loose.

 

I've had a look and the seem tight to me, could be there is a lot of flex in the steel mounting? 

[Eeyore]

I will have to go with Loddon on this. The mounting arm is attached to the main engine mounting beam; its this beam that appears loose on the engine. You may need to remove the mounting arm to gain access to the set bolts attaching the front of the main engine mounting beam to the engine. Shut it down and try rocking the front of the engine whilst checking for movement as indicated by the arrows in Loddons post.

 

 

[spicemouse]

We have a winner! The mount has broken, it's behind the arm so quite hard to see but just visible, though hard to photograph. 

 

 

1) could this have been caused by alternator vibration, or more likely a long term stress fracture? 

 

2) what on earth do I do now.. 

[Alan de Enfield]

13 minutes ago, spicemouse said:

what on earth do I do now.. 

 

 

If that is the actual engine mount

I'd say Don't run the engine, if 'one corner' is broken there are going to be all sorts of stresses on the other 3 corners.

It needs fixing.

 

If it just the mounting for the alternator, get a man with a mobile welder in.

[spicemouse]

Just now, Alan de Enfield said:

 

 

If that is the actual engine mount

It's an engine to mounting frame mount. Which can also be welded? 

[Tracy D'arth]

Get it welded and re-enforced or it will crack again in the same place, you have to redistribute the stress elsewhere. 

[Alan de Enfield]

1 minute ago, spicemouse said:

It's an engine to mounting frame mount. Which can also be welded? 

 

Suggest you find a 'mobile welding man' (or are you close enough to a marina) and get it done ASAP.

[spicemouse]

Thanks all. I'll get on finding a mobile welding chap. I'm out of water, but otherwise in a reasonable place to stop. I'll let CRT know if I'm stuck. 


 

1 minute ago, Tracy D'arth said:

Get it welded and re-enforced or it will crack again in the same place, you have to redistribute the stress elsewhere. 

Another bracket maybe? Three per side? 



Also, you'd have thought they'd have picked this up when it was remounted 2 months ago? Unless the remounting is what triggered this. 

[Eeyore]

Looks like the "best" way it could fail; loose bolts could have given a much bigger headache.

There are things in your photo that say this is not the first time that it's failed; no paint on the washers and what looks like a strengthening plate ( obscured by the dipstick tube).

You'll need to remove the top nuts from the new engine mounts and jack it up in order to get the engine mounting beam out.

The alternator mounting beam can probably be left attached as long as you disconnect and remove the alternator.

Make sure that the beam sits equally on the engine mounting points before you fit the bolts otherwise the whole thing will twist as you tighten the bolts, which is very likely to have be a contributing factor in the failure.

Edited June 25, 2021 by Eeyore