91 520-H mower question

[rollingflat 123]

Hey fellas i have a question for you all, I just finished rebuilding the 60" mower deck on a 520-H i got last fall. Its a 91 and has the skids w/o any scalp wheels. 
Anyway got it mounted and mows great except it will just up and stop spinning somtimes? the belt from the engine pully to the deck is supper tight, I think the drive belt from tractor
to engine pully/cluch is slipping? does that sound right? if so how do i tighten that belt? thanks for any help!

[boovuc 1,090]

Put some slack in the drive belt to the mower. It shouldn't be tight and it will jump around while mowing. (That's normal). I'll assume since it was rebuilt that nothing is tight including the mule drive pulleys?
Also make sure your PTO is adjusted so it "is" tight to the bell when the PTO lever is all the way engaged.
If your belts are old, you may need to replace them. The 60" deck is a lot for the belt(s) to lug.  

[rollingflat 123]

Boovuc thanks for the quick response Ill loosen the drive belt. I made that supper tight. and ill try to adjust the pto,

thanks! Ill let you know how it turns out!

[cheesegrader 433]

I ran the exact same setup to mow last year!
Check the bearings in your mower spindles.  Not too tight to turn by hand pulling your deck belt, not sloppy/wobbling/pistoning up and down.
Do you have the srping-loaded mule drive specific to the 60" deck?  It makes a huge difference on belt tension when the deck is raised and lowered.
You can use the regular mule, but you have to set the tension with the deck down, and leave it there.
Like boovuc said, check the PTO tension, and mule drive bearings.
That deck is darn hard to drive.  If anything in the drive train is a little tight, or slips a little bit, it stops working.