Serpentine belt tensioner shaking

[cidades]

Hi there, I'm trying to figure out what's the problem with my car. It had a little tensioner movement at idle.. So I though that it maybe the alternator pulley and replaced it by new one(INA brand), it improved a bit. Next I replaced the tensioner with damper and the belt it self with no improvement at all.

With the alternator electrically disconnected the tensioner stops shaking, can it be a problem with the alternator itself?


I'm sorry for my English.
Thanks

 

[compu_85]

Some movement at idle is fine. Is the shock absorber getting very hot?

-J

 

[cidades]

I will check if it gets hot.

It moves about 0,5cm each side, very fast. I have compared with a friend's car, with the same engine and it barely moves at all.



Here is a video:
http://youtu.be/MHR4XJcDE3E

The shaking is very fast, my phone can't capture it well.


edit: It does not get hot.

 

[compu_85]

Looks normal to me. If the alt pulley isn't working properly it puts a huge load on the damper which will make it get super hot.

-J

 

[cidades]

Ok, thanks man.

I thought if everything was OK the tensioner shouldn't move at all.

 

[[486]]

I could see an open winding in the stator of the alternator (or one bad section of the rectifier) causing it to make the belt bounce a bit.
Make it jump a bit every time it comes around to the "dead" section.

Load test the alt, if it puts out less than full output you can know it has issues.
If you're the type to have an oscilloscope, clip that onto the output stud of the alternator and look at the waveform it puts out.

 

[cidades]

Thanks, it's a good bet I guess. I doubt it could be a open winding, but diodes fail very often.
Next week I will try to borrow a oscilloscope and analyse the output waveform of the alternator.

I'm expecting a wave like this green one, right?

 

[cidades]

Just made a homemade oscilloscope, here is my alternator's output waveform:

Doesn't look that bad I think. What do you guys think?

 

[[486]]

That looks good to me.
A single bad diode would be missing 1/6 of the peaks, two bad ones would be missing 1/3 and so on.

As an aside, I'm seriously impressed every time I run into someone that knows what a scope is and how to use one.

So, the last bit before I'd call it good, is the crank pulley spinning true? Some crank pulleys put the belts on the harmonic balancer's outside part rather than its hub, and the rubber can deteriorate over time and make it do all kinds of strange things.


ETA: Just saw the video, doesn't look out of line to me at all, when it starts bouncing around a centimeter at a time or so is when you should worry. These engines do not have near the rotational mass a normal diesel engine would, and so they don't run very smoothly at all.

 

[cidades]

The crank pulley/harmonic balancer is spinning true, can't see anything not right on it. It looks the vibration is coming from the alternator, it only happens when there is electrical load on it. Can it be a bearing?

Anyway, I will stop to be worried about it and start drive, if it get worse then I will try to fix it.

 

[compu_85]

Anyway, I will stop to be worried about it and start drive, if it get worse then I will try to fix it.

Drive more, worry less

-J