Mowing Kubota TG1860 PTO Belt comes off when operating on fast speed

BMBUK · May 17, 2017

Hi
I'm new to the forum, and desperate for some advice on how to fix this problem. The PTO Spring snapped so I bought a new one (very expensive). However, since then, the PTO belt keeps coming off when I run the Mower at fast/full speed. So I can use it if I run it at half speed but unfortunately this isn't fast enough to power the grass collector (GCD360), so it keeps blocking up.
The spring is correctly connected, and the tension arm is in the correct position. Can anyone suggest how I can fix the issue with the belt coming off?

redman135 · May 17, 2017

It sounds like your belt pulley's are out of line. Can you eyeball from 1 pulley to the 2nd pulley in a straight line or is it offset vertically, if so then you need to figure out why the pulleys are out of line then fix them. Also check the belt. It should be smooth all the way round. You may have a partial break in the belt on the inside and as the belt speed increases is enough to make the belt jump off the pulley.

BMBUK · May 17, 2017

Hi Redman135
Thank you for the fast response. The belt is not very old and in good condition, no breaks, splits etc. So it must be something to do with the pulley alignment. They look aligned, but the main pulley on the cutting deck (RCK48TGEC ) that the belt goes around does appear to have a small amount of movement in it - do you think it could it be that?
Regards.

redman135 · May 18, 2017

Hello BMBUK, could you post some photos of the belt/pulley's from the side and from the back, including the tensioner please?
You state the main pulley has some movement, how much and what direction?
What pto revs are you running when the belt jumps of? Are the revs the same every time?
What revs does the mower run at?

Grandad4 · May 18, 2017

It could also be one of the pulleys is not turning correctly so it sets up a vibration at high speed. Possible cause would be a bad bearing. Try observing how it runs to see if it sets up a vibration as you run up the speed. Be careful if you leave the pulley covers off to do this, of course!

BMBUK · May 25, 2017

Hi Redman135 and Grandad4 - thank you for your responses and apologies for the delay in getting back to you, I was out of town all last week. I will try and provide some photos as requested. The main pulley has movement in all directions, also, the revs are at about 50% when it jumps off, and it's the same every time.
The pulleys are all turning smoothly, but it does appear to vibrate a lot, and gets a lot worse the higher the speed.
Do you think it's the bearings on the main pulley on the cutting deck?

RjCorazza · May 25, 2017

My neighbor has that same mower, and it has had belt problems since she got it. In her case it's the drive belt, and I am convinced it's a design problem.
Anyway, some other things to check (particularly with jumping belts) :
Check the inside crevice of v pulleys for wedged debris
Check all pulleys for smooth operation, and for the ones that may have the pulley halves rivited together, check that they are in fact rivited securely by checking top and bottom. I just found the bottom rivit heads of an idler pulley almost all gone on my walk behind mower. It was causing the belt to jump all over the place, and was not detectable (to me) by looking at the top or spinning it with the belt on.