Stop rear drive belt from breaking!

Hi!  
I've been working on a speed-upgraded mower for riding around on and off-road.
The mower is a bolens, by MTD, but it's identical to the troy-bilt mower in Chud327's video here
I removed the governer as well, and have been driving it around 15 mph.
As I was driving it the brand-new rear belt just snapped and flew out of the mower! I found the belt and it's doesn't look like it was worn out, it just broke apart! Perhaps I need to put a different pulley on the back or remove the tensioner altogether? Please help!
Below is a picture of the rear pulley setup.

Almost sounds like excessive tension. I wonder if maybe as the variable pulley changed geometry if it was too tight for the belt? Spring too strong? Idler too large?

Rustbucket Garage wrote:

Almost sounds like excessive tension. I wonder if maybe as the variable pulley changed geometry if it was too tight for the belt? Spring too strong? Idler too large?

That could be it, but I'm not sure. This belt was, if I remember correctly, it's 35*5/8 inch belt, which is what the guy in the video used. I don't know what the old belt size was, but the old one popped off instead of snapping, so I think it was somewhat loose.
The belt also rubbed somewhat and became very hot.

Something I have run into in the past on these varidrive systems.  That small idler that is on the arm that keeps tention.  Over time that arm will bend up or down maybe even twist due to stresses and use.  Check to make sure that pulley is still in alignment with the FNR transaxle pulley.  If not, it can jump and throw the belt.  Maybe look into making a (better) guide than stock for it and the transaxle to help keep the belt in the groove.

MightyRaze wrote:

Something I have run into in the past on these varidrive systems.  That small idler that is on the arm that keeps tention.  Over time that arm will bend up or down maybe even twist due to stresses and use.  Check to make sure that pulley is still in alignment with the FNR transaxle pulley.  If not, it can jump and throw the belt.  Maybe look into making a (better) guide than stock for it and the transaxle to help keep the belt in the groove.

Do you mean bend vertically? like higher or lower than it should?
Is it possible to just use a smaller belt and ignore the idler altogether?

Yeah, sometimes they get higher or lower. I'm sure it is required to keep the belt tight against the variator pulley, and be able to keep that tension as it changes the belt ratio to go faster/slower.  Without it, the tractor would not go as the belt would just slip until the variator ratio gets to the point friction is achieved again.

Yours could be ok, and it could have been a bad belt if no wear and just simply broke.

Ok, the idler pulley was bent!
I fixed it and had to find a new belt, so that took a while, but now it is in working condition again! (mostly)
thanks