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I am having problems with my MTD RS 125 model: 13D1452F600

Does the belt follow the green or the blue line.
I have tried both, and the tractor doesnt really move, besides a tiny bit if it is in 5th gear.

Generally speaking, the tensioning idlers I've seen tend to move the belt in a direction that causes more pulley-to-belt engagement.

The blue line looks like it would have about 180 degrees of engagement. I've seen worse designs. Much worse.

But the green line looks like it would have almost 270 degrees of engagement, or 50% more than the blue line. Much better.

I'll take the green line.

But if the tractor won't move no matter which way you install it, there must be some other problem. Sure you have the right belt?

Look at the groove in the tension pulley.
It is flat
So the back of the belt runs on it.
And that is the no exception rule flat = back V = front

So in your case it is the green line.
The previous post while it sounds obvious is more honoured in the exception than the following

Good thing you don't have a double V belt like I do.

I can't get a reference point to know how everything is set up. A further way picture of the mower might also be handy for a reference. Is it possible that the idler pulley gets pulled to the right and the blue line on the right gets put on the left side of the pulley. Also Bert, the flat on flat isn't absolute, MTD has a habit of using the inside of their 5/8 transmission belts on flat idler pulleys. Years ago all the variable drive mowers used a flat idler on the rear drive belt of their riders.

ILENGINE said:

I can't get a reference point to know how everything is set up. A further way picture of the mower might also be handy for a reference. Is it possible that the idler pulley gets pulled to the right and the blue line on the right gets put on the left side of the pulley. Also Bert, the flat on flat isn't absolute, MTD has a habit of using the inside of their 5/8 transmission belts on flat idler pulleys. Years ago all the variable drive mowers used a flat idler on the rear drive belt of their riders.

Click to expand...

Foot in mouth exits stage left to go fix a concrete saw.
Always happy to be corrected, thank you.

Im showing the idler pulley goes on the right hand side of belt. Where it is now is the left. So pull it way over and towards the front of the mower.

What the boys are trying to say is there are a few variations of the Idler pulley position.
The rear idler has to put a constant tension on the belt.
Thus it will go on the side where the spring is pulling against it to tighten the belt
So whichever direction you move the pulley to stretch the spring, the belt goes on the other side so the spring is pulling on the belt.
Thus if moving the pulley to the left stretches the spring more then the belt follows the green line.
Conversely if moving the pulley to the right stretches the spring more then the belt follows the blue line.
If there is no difference moving the pulley left or right then the spring is in the wrong place.

I found a diagram that shows where it goes.