Drive belt on Craftsman tractor will not stay on

[BJO]

My brother and I replaced my tractors engine with a newer engine, now my drive belt will not stay on after I stop and move to a new gear. I put the belt back on a number of times and it kept popping off. When I was checking the composite and idler pulleys they seemed like they were not aligned with each other. One felt like it was higher by ~1\4 inch. I replaced the drive belt because when this first happened I thought the belt had broken, it was the original belt and my tractor is almost 20 years old. After changing the engine I almost got the whole yard cut when the tractor stopped, I really think the mower God’s have a beef with me or Mother Nature does not want a hair cut. My question is are the pulleys supposed to be lined up and is there a way to adjust them?
Thank you in advance
My tractor is a LT1000, but I forget what the new engine is.

 

[bertsmobile1]

he trans pulleys should all be in alignment.
If you took the pulleys off, check you did not put them on upside down.
They have a top hat bush inside the inner race which spaces the pulley.
Easy thing to do on some mowers .
Other than that, did you put the keepers back around the drive pulley ?

 

[BJO]

he trans pulleys should all be in alignment.
If you took the pulleys off, check you did not put them on upside down.
They have a top hat bush inside the inner race which spaces the pulley.
Easy thing to do on some mowers .
Other than that, did you put the keepers back around the drive pulley ?

Thank you, I’ll have to check on this Thursday or Friday, I think we did pull off the v-grove pulley and that is the one that is slightly lower. As far as the keepers they did go back on — there were no extra parts left over — we just had to loosen them. Thank you again.