GT 3100 Engine/PTO alignment?? Front PTO belt comes off.

[Joelk]

I recently bought a 2005 GT 3100. It seems to be in pretty good shape/works well except for an issue with the front PTO belts.

The prior owner told me there was an issue before I bought it. Said it would usually mow short grass without, but PTO belt would come off if it got into tall grass.

The PO had replaced the vacuum actuator and PTO Idler Pully(Old one came with the tractor and did not seem to be bad), but said the problem continued even after replacing the parts. I looked at the alignment before operating it and it appeared to be pretty good and nothing appeared to be bent or loose.

I mowed for about 1/2 hour and it seemed to be working fine, then the front belt came off the idler pulley and started getting chewed up. I pulled the hood/muffler etc. off the front of the tractor and could see a very slight misalignment of the Idler pulley(used straight edges to check) vs. the engine. It does not look like it would be far enough out of alignment to cause the belt to come off, but apparently it is.

I pulled the engine out of the tractor to do some other work and have the engine installed with the bolts in, but not tightened. I tried twisting the engine and it seemed to move a fair amount(I saw no wear in the engine or frame mount holes/bolts) and am wondering it there is recommended procedure for aligning the engine. If there is not, I will probably try twisting it to the position that provides best alignment of the belts on the PTO actuator pulley.

Any other suggestions on how to improve the alignment?

With belts costing about $50 for a pair, I would like to get it fixed on the first attempt.

Thanks, Joel