Ok this is getting to emergency/crazy level. :-(

So the Gates 6738 Belt that was stated as being a replacement for the Victa CH85678A, which after my asking on here and best research showed as being the correct belt for a 550 Pro. Cut a long story short its massively loose - like not even close to fitting!

They're going to have to be returned or sold - not a huge issue right now - as it's a week after I yet again pushed a utility around the entire acre and I need to mow yet again. :-(

So I would greatly welcome any guidance as to how to logically solve this issue.

In no particular order here's what I know from trying:
- M36K and M36(rubber) belts are far too tight, tension arm can not even move with these on
- M37 (Carlisle wrapped belt) was too loose as well - will retest this
- Gates 6738 belt (CH85678A - M38) massively loose
- I will measure the size of the front and rear pulleys but am pretty sure they're stock sizes as I have 2 'working' 550 Pros and they're the same size on both of them.

I only have one belt that 'work's on the mower and due to a tear in it I'm replacing it - I'm unsure of what it's size is - but do I cut and measure it somehow or do anything else to ascertain what model it is? Due to it's age/wear there's no markings on it to ID.

Real bummer and kick in the guts as I was sure all that reading would ensure the correct result but I'm now more lost than ever.

Thanks in advance for any guidance or ideas.