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First off, if I'm breaking any protocol for the message board I apologize in advance. I'm hoping to get some help as a new home + mower owner. I have a 746 SRL Yard Machines 46" deck mower (Model # 13RL771H). I needed to replace the very highest belt (closest to the seat) which I believe is the PTO belt. The one I had broke and then the blades would not engage when I moved the PTO switch. It is the belt that goes through the forward most pulley.

After some confusion on which belt I needed (I bought one that was far too short), I ended up buying the Stens belt on Amazon which is listed as MTD 954-04142 and is 91.5". I found the routing for the belt in the manual and the image I used can be found below. I got the belt routed properly, at least as far as I can tell, and the PTO would engage.

However, I got the mower out into the yard and tried to drop the deck/blade length into setting "3". I could feel the PTO disengage and the blades stop spinning. I turned off the PTO, put the setting back in "5" and re-engaged PTO...the blades started back up. I decided to go one level at a time and the PTO/blades stopped running as soon as I went from "5" to "4". I had someone do that process while I watched underneath and kept an eye on the belt, but I couldn't see anything happen to cause the stop. Is it losing tension somehow? Is that even the right belt? Any ideas on other causes?

I was able to mow the entire yard in the "5" setting and it really never acted funny...but as soon as I got done I tried dropping it into "4" again and the blades stopped. I've never owned a riding mower so I have no clue what I'm doing, so any help would be appreciated. Thank you!

Well, changing the deck height does change the angle of the belt, but that does seem peculiar. The only thing I can think of besides belt angle/tension is perhaps the electrical connection for the PTO or the wiring are moving/getting bumped/pulled. The belt isn't hitting your PTO wiring, it is it?

With most mowers the belt & mower pulleys are in line at the middle setting ( 3 in your case ).
Because most decks go strait up & down as the deck gets further away from in line the distance between the pulleys gets bigger and the belt tension increases.

The classic test for a worn out belt ( or tension spring ) is to raise & lower the deck listening to differences in the blade speed.

So in your case, the tension spring is not pulling hard enough on the idler pulley

From what I can gather that is the correct part number of the belt. With the mower off and the pto engaged with the deck all the way down reach under there and see if the belt is actually loose or if something else is going on. Let us know see we can figure this out. It looks like there is a spring between the two idler pulleys. make sure it is connected also. If that spring is missing it may be allowing the other idler pulley to move too far forward causing your loss of belt tension if this is what is causing the issues.

First off, thanks to everyone for the comments. I think it's a tension issue. Even when I have the blades on the highest setting (5) and the PTO engaged, there's quite a bit of slack on the belt. When I change down to "4" or lower, the belt definitely stops moving completely. Should I just be looking at the two springs that are visible on that diagram I posted in the original post? I see one running from near the belt cover and another that is basically in the middle of the deck. Is there any way to tell to verify that they are the issue? And if so, can you tighten them up or are new springs generally necessary?

Start by double checking that the belt is actually on all of the pulleys.
Very common for it to drop off the left or right pulley which you can not see cause they are under the belt guards.
Check the tension arms.
The holes flog out oval and they can prevent them tensioning the blt properly.
Also double check the springs are in good condition, the mounting points have not worn and they are actually in the right holes.
Again check that the springs are in their correct holes as deck parts are shared between different size & style decks so some parts will have multiple spring mounting holes.

I'll check the springs. Is there any way to really know if they are in the correct setup? Also, on the "tension arms", where are those exactly? I think it's definitely a tension issue and for whatever reason, dropping the deck is making the belt lose tension. I'm going to try and trouble shoot this tomorrow. I need to mow pretty bad after some heavy rain...so hopefully I can get it sorted out. Thanks again.

The usual fall back position is to check the parts diagram which in this case can be a tough confusing.

Looking at this diagram https://polr.partstree.com/v1/iplimage.php?ir=YToyOntzOjk6ImltYWdlUGF0aCI7czoyNDoiYlhSa0x6YzJPVEF6TnpNMFhEQXdNRFU9IjtzOjc6Im9wdGlvbnMiO2E6MTp7czo1OiJ3aWR0aCI7aToxMDAwO319 you will see 2 pulleys part No 64.
When you pull the PTO lever it moves a cable that ultimately moves those pulleys backwards to make the belt tight.

So follow the PTO cable around and make sure it is clamped correctly and engages with the plates # 7 and # 8.
Both of these must be free to swivel, a little grease on the pivot axels # 75 & # 52 works wonders

bertsmobile1 said:

The usual fall back position is to check the parts diagram which in this case can be a tough confusing.

Looking at this diagram you will see 2 pulleys part No 64.
When you pull the PTO lever it moves a cable that ultimately moves those pulleys backwards to make the belt tight.

So follow the PTO cable around and make sure it is clamped correctly and engages with the plates # 7 and # 8.
Both of these must be free to swivel, a little grease on the pivot axels # 75 & # 52 works wonders

Click to expand...

Great stuff...I'll be taking a look at the pulleys and plates today. Honestly I think I may have to get outside help on this due to my inexperience, but I'm giving it a shot and learning a bit in the process. I'm sure someone that specializes in lawn mowers/tractors could get this diagnosed and fixed relatively quickly. Thanks for the help!

It is a dicky set up on that deck.
There are only so may ways you can run a belt and the simple ones are all patient.
The profit margins on mowers was not great so designs that were royalty free were top on the design requirements.
Pull the deck off and have a good look.
Where springs were attached there will be wear marks and usually a sort of line.
Similar for belts, the belt will eave marks where it rubs on painted parts.

When it is out, take a good photo of it in one frame, covers off and post it.