Possible causes for balance belt breakage

[Miles Frederick]

The reason I'm doing the timing belt is that my balance belt broke, taking out the water pump (or at least it failed too).  The damage is not to the teeth, but completely snapped.  The timing belt itself luckily wasn't damaged.

What are the possible reasons for this having happened ?

~75000KM and about 5 years since the last timing belt job, oem parts.

As well the balance shafts seem to turn freely by hand.  Can this type of thing just happen without a reason ?

As for balance shaft delete, I have intentions to do so in the event the engine is ever rebuilt again, but was hoping to not have to deal with the removal w/ the car on jackstands..

[Jason Harwood]

Balance Shaft belts have been known to pop.
Which is why most people who do builds remove them.

[Brett Haviland]

what i have seen it that the water pump starts to leak... the coolant seeps down in to the b-shaft belt tensioner bearing, siezing it up, which then shortly afterwards the b-shafts belt snaps

[Chad Giffen]

You should be servicing at 75,000km anyways.

I would. Just rolling the dice after that.

[Brett Haviland]

i always recommend changing the t-belt and assesories at like 50 000 km's if the car is driven/reved hard.

[John Hartman]

its 90k factory, but if you are competing with it, maybe sooner. Or if you have stronger valve springs or bigger cams.  Those don't effect the b belt tho, so look for leaks or damage to the b belt pulleys/tensioner.

If nothing is siezed, and its not wet with oil or coolant, you may have just gotten a bad one?

I had one break on me(I didn't change it, it was long time ago and I payed someone else to do it) and it was just ripped in half, not a clean break.  I think he over tensioned it, as there was always a slight whine to it from when I picked it up.  Well, until I noticed a vibration at around 3 grand...