100 Balanced Head Mower

A couple of questions regarding the 100 balanced head mower.

1) How do you install/adjust the drive belt? The idler bracket isn't slotted and only has a fixed hole for the pulley. I don't
see anything on the PTO pulley or head assembly pulley allowing movement to install or tension. I don't have the new belt yet
so maybe it's as simple as strong arming the belt onto the idler pulley but I would still think there would be something to
allow proper tensioning.

2) Regarding the idler pulley. It's a flat pulley suggesting the back of the belt rides on it. However in most photos and IH
literature it shows the belt running over the pulley which puts the V side on the pulley. I've seen a picture or two showing
the belt running under the pulley which puts the flat side of the belt on the flat pulley.

Thanks in advance for comments and advice.


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On mine the drive head assembly will pivot for belt tension. The belt idler will work either way, I have a larger idler pulley on mine when the original one died, it's on top. The idler bracket U bolt will allow the idler pulley to be moved for some adjustment too, I just replaced the belt on my 9 foot mower taken from one of my parts mowers I got from a recent auction.
The belt is supposed to run over the idler. That's there to keep a little tension on the belt to prevent flapping. It also helps the belt run straight when the wobble box is pitched all the way forward. It is supposed to be adjustable, up or down, but usually gets replaced with whatever will hold the pulley up in a hurry if the old one broke.

The main belt adjustment is on the hinge frame. There's two bolts under the PTO that need to get loosened up. Don't take them out. They're the same ones that are holding the cutter bar rest on the machine. Once those are loose, you can adjust the belt tension with the eye bolt nut. That bolt is the one that points to the wobble box. The manual shows the eye bolt is double nutted with a lock washer in between.



The third pic doesn't want to cooperate.... nor the last one!!



The upside down instructions are for the slip clutch pulley. The tension (1/2 in.) is the same for the non clutch pulley & the slip clutch pulley for the hay conditioner PTO.

I always thought you slid the idler out toward the wobble box to add tension to the belt.

Agreed, the belt runs OVER the idler. V-belts are not meant to run under the idlers. You can get away with it in low angle, low tension applications but if you are really pulling down on the outer surface of the belt, the belts break down and fail quickly.
Agreed. The older/earlier units are adjusted that way - simple enough with a crescent wrench that doubles as a hammer to slide the bracket. If I recall correctly later units had a slot on the bracket
that holds the idler pulley to adjust tension with a single bolt.
Picking the belt up tomorrow and getting a new idler pulley on Thursday. Sliding the bracket along the rail for tensioning makes
sense in its simplicity.

Thank to Mike, BYEngineering and others for your help.

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