Alternator belt snapped after 3 weeks

[NatLE]

Three weeks ago I had my engine serviced, alternator replaced and the belt too.

It snapped yesterday whilst I was charging our batteries.

 

Is it possible that the new alternator isn't correctly aligned? Or the belt was to tight or just duff? Or is the alternator to big for the belt.

 

Running on a BMC 1.8.

One 10mm belt for water pump and 90amp alternator. They said they would usually only fit a 70amp alternator to that size belt (to which I said "that's fine") but they ended up sticking a 90 on it (Which is what was on there before and I was going through a belt once a year or so...)

 

I have a recently installed a Stirling alternator charge controller, I think that this increases the load on the alternator, so that might be why it's too much?

 

There isn't any room increase in belt thickness or add an additional belt as the engine is right next to a bulkhead, so the whole lot would need moving backwards...

Presumably possible but pricey?

 

 

Any ideas?

 

Should I just buy a smaller alternator and get someone to fit it? 

[matty40s]

Get rid of the sterling. 

[BEngo]

90 A is about the limit for a 10mm belt.  But, before going drastic:

Check the pulleys are aligned.  Both grooves in line and the alternor shaft parallel to thd engine centre line.

  Is one side of the snapped belt shinier than the other? Try to get a straight edge across the pulleys for an eyeball of the alignment.

 

Are the pulley grooves clean and shiny? Rusty ones will soon wreck a belt.

 

 Is the belt tension right.  An over tight belt does not last long, but nor does a slack one.

 

Try switching the Sterling off for the first 10-  20 minutes of running.  The benefit of the Sterling is af the tail end of charging so it will not mean running longer if you only switch off at the start.

 

N

[Eeyore]

What @BEego says, plus, an alternator pulley turned from solid rather than the two piece pressed ones. The pressed ones flex a great deal when used with the necessarily high belt tension. This flexing causes the belt to travel radially in the pulley as it traverses the arc of contact. The failure mode was very likely to be related to not re-tensioning the belt after the initial running in period; look for a blue (overheating) mark on the alternator pulley. This would show where the load on the alternator was sufficient to hold it stationary whilst the belt slipped.

[Tracy D'arth]

90A alternator on a Sterling controller is fine, have run the same for years. My belt is at least 10 years old.

There is nothing wrong with Sterling controllers, it is fatuous to suggest so.

You have a misalignment or the belt was badly fitted from new, Gates belts are much better than others.

Is there loads of black belt dust around?

Edited November 30, 2023 by Tracy D'arth

[NatLE]

 

14 minutes ago, Tracy D'arth said:

Is there loads of black belt dust around?

Yep loads of belt dust. There's always a bit, I'd assumed a little bit was fairly standard as it wears? But there's a lot...

42 minutes ago, Eeyore said:

an alternator pulley turned from solid rather than the two piece pressed ones.

Am I looking for a seem inside the channel the belt runs in to check if it's a two piece pulley?

[BEngo]

Loads of belt dust equals loads of slip.  Usually either, insufficient tension, or,

Misalignment, or,

Wrong type belt( not cogged when it needs  to be), or, 

Insufficient belt wrap, or,

Worn belt.

 

All the possibilities lead to the last one anyhow.

 

 

The join is in the root of the V groove, yes.  The two part pressed  pulley is fairly obvious when you look at them.  They look flimsy when compared with a turned from solid item.

 

N

Edited November 30, 2023 by BEngo

[Tony Brooks]

12 minutes ago, NatLE said:

 

Yep loads of belt dust. There's always a bit, I'd assumed a little bit was fairly standard as it wears? But there's a lot...

Am I looking for a seem inside the channel the belt runs in to check if it's a two piece pulley?

 

Yes, or spot welds on the face, or seeing the circumference slightly turned outwards so it gives some rigidity to the sheet metal. Solid pulleys tend to have the inner and outer face machined flat, whereas two piece pulleys are usually fairly deeply dished.

[Eeyore]

The dark one shows the typical appearance of a pressed pulley. The silver one is turned from solid.

[Ex Brummie]

3 hours ago, BEngo said:

 

  Is one side of the snapped belt shinier than the other? Try to get a straight edge across the pulleys for an eyeball of the alignment.

 

 

 

 

 

N

Both sides of the belt will be shiny if misaligned, polished by different pulleys