RM48 deck belt routing improvement

[thebuildist]

I don't like the deck belt routing on my RM48 deck. On my old J44, I never had any problems with the deck belt slipping.

But on my RM48, I've now changed the belt twice, the first time fixing a hack the PO did, probably because he was having problems too.

The PO had abandoned the factory belt tensioning method,

and just went with a belt that was fairly snug right around the three pulleys.

I mowed with it like that for a month or so, but I could hear one or more blades slow down when I got in thick stuff.

When I investigated, I ordered the correct belt (82" long) and installed it correcly.

But I still felt like the blades slow down too easily.

I ran it that way for a season and the next time I checked, it was completely shot. This time I ordered a kevlar belt to see if that helped.

So as of today, I can see that the problem is still present, it's just way too easy to slow down the blades.

Experience with other decks/manufacturers tells me that in the factory design, the belt doesn't wrap the center pulley enough. A 1/4 of the pulley just doesn't provide enough grip.

So what we need to do is move the idler pulley farther to the left, so that the drive pulley has the belt wrapped more like halfway around it.

It'll be simple cutting/grinding welding, to just move the idler arm/pulley over there.

But right now I have the deck installed, and it is usable, and I have a lot of leaves to blow and suck up. (The new high-lift blades are awesome while they're spinning.)

So I don't want to pull my deck this instant. And I need to order a belt in advance, ready to do the work.

But what belt to order?

I began by drawing my current belt routing in CAD. I know that I have 17" blades on the outers, and that they cover a 48" swath. And I'm pretty sure the deck pulleys are about 4". So I draw in those two pulleys.

Then I know that the center blade is forward far enough for the blade tips not to strike each other, so I draw that in.

From there I draw in the (I'm guessing) 5" idler pulley, and draw connecting lines to represent the belt.

Time for a sanity check: I know that the stock belt is right around 82". So I add up the lengths of the straight belt, plus the arc lengths where the belt wraps the pulleys. And it all adds up to about 82". So my model isn't insane.

Then all I have to do is move the idler pulley over to where I want it, and re-do the belt measurement process.

And it comes back to about 98". However: I don't want the idler any farther to the left. And the idler might be a little smaller than 5".

So I'm going to fudge downward to 96". I'm perfectly confident that I can find a pulley location that'll work with that belt length.

I'll report back some time next week with an update and some photos of the finished process.

Bob

[Eugen]

You are brave and determined to do this mod Bob. Very cool! I'd have measured the pulleys and distances though.

[propane1]

I would put an stationary idler over there on the left. That way it would wrap around the left pulley more and around the centre pulley more. Just a thought I had. And my drawing is not very good.

Noel

[DavidBarkey]

Both Bob's and Noel's ideas a widely used across the industry . Both have there merits. Bob's has one less part while Noels would be simpler . The lack of contact on the drive pulley is a definite design flaw . Good on you Bob for recognizing it and wanting to fix it .

[propane1]

The deck on my Case 224 is the same way other than it’s opposite. Deck belt only wraps around the centre pulley about 1/4 the way. I thought that was my trouble when the blades were slowing down because of the belt slipping. But it turn out that my slippage was coming from the engine to deck belt. I didn’t have it tight enough. Once I adjusted that it worked fine. No slipping in the heavy grass.

Noel

[thebuildist]

Good observation. Presumably my old L44 deck had the same routing and I just never noticed a problem.

But in this case I had just installed my deck, and the main drive belt was plenty snug.

And when I reach under the deck and wiggle one of the blades, I can very easily make it slide while leaving the other two blades stationary. That tells me that I don't have a sticky enough connection between the blades, so it seems natural that that's where my slipping is coming from.

Now, I'm not guaranteed to be correct. But it is observable that the current belt routing/tensioning is less than ideal. So I'll address the visible defect/issue, and then see if that resolves the overall problem.

Thanks for the info.

Bob

[MattA]

Bob - I modified by RM44 and then my RM48 belt drives back in 2017. I used Noel's method for both decks but later thought of using your method. The only reason I didn't use your method is that I don't have a welder and I would have had to coordinate with a friend to do it which just delayed my project. I think your method is the preferred method. Anyways I received a lot of push back from users on the old forum for doing this. They essentially stated I was the only one with the problem and the belt drive was sufficient for 1000's of users which both of us disagree with. One thing they were right about was my center drive spindle was worn out and needed replacement. The pulleys were pitted and worn down.

RM44 deck - I only ran this setup for maybe a year before finding and rebuilding my RM48 deck. I sold the RM44. The one issue I had was with the belt creeping up on the idler pulley I added. I ended up shimming my pulley setup to fix this.

Standard belt tension. Tensioner spring is stretched 3.76".

Mounting bolt bottom side

Initial mounting bolt setup. Those are 0.25" thick washers.

Shimmed mounting bolt

Modified tension. Tensioner spring is stretched 4.238".

Modified belt drive

Belt riding up on the pulley

Plan B (shift the pulley more to the left)

RM48 deck - I've ran this setup for the past 4 years. I do not have the belt creep issue on the idler pulley with this deck. I did have the bearings go out on the added idler pulley and ended up replacing both idler pulleys (this year?). Both idlers were new stens replacements in 2017. I also still had issues with both belts slipping on the center drive pulley even with my modifications but only in thick deep grass. After one bad mowing I had black dust all over the deck and mule drive. The main drive belt was toast and the internal drive belt had signs of slipping. I replaced the center drive spindle with a RM38 drive spindle (faster speed) and now neither belt slips. My 16HP vanguard just looses RPMs now when in deep grass. My outer spindles are also pitted. One slips more than the other causing the blades to drift in and out of sync every few seconds. I just bought replacements from Bob but haven't installed them yet. I've also had issues with the internal tensioner bracket bushing wearing out and seizing to the bracket. I've replaced it twice and the last time I drilled out the bracket and used a beefier spare bushing I had laying around from the mule drive.

RM48 deck with modified belt drive. The belt is a Gates High Power 2 A83.

Closeup. Tensioner spring is stretched 4.565". The added pulley may be a little too close to the center drives spindle?

End ramble

Make sure you have adequate tension on the internal tensioner spring. I'm also not a fan of the factory RM48 drive belts. Every one I've bought from various vendors was old dried out rubber. I'm happy with the Gates High Power 2 belts I am using.

[propane1]

Great ramble Matt.


Noel

[thebuildist]

Bob - I modified by RM44 and then my RM48 belt drives back in 2017. I used Noel's method for both decks but later thought of using your method. The only reason I didn't use your method is that I don't have a welder and I would have had to coordinate with a friend to do it which just delayed my project. I think your method is the preferred method. Anyways I received a lot of push back from users on the old forum for doing this. They essentially stated I was the only one with the problem and the belt drive was sufficient for 1000's of users which both of us disagree with. One thing they were right about was my center drive spindle was worn out and needed replacement. The pulleys were pitted and worn down.

RM44 deck - I only ran this setup for maybe a year before finding and rebuilding my RM48 deck. I sold the RM44. The one issue I had was with the belt creeping up on the idler pulley I added. I ended up shimming my pulley setup to fix this.
standard-tension.jpg
mounting-bolt-bottom.jpg
initial-mounting-bolt-setup.jpg
shimmed-mounting-bolt.jpg
modified-tension.jpg
modified-belt-drive.jpg
belt-riding.jpg
plan-b.jpg

RM48 deck - I've ran this setup for the past 4 years. I do not have the belt creep issue on the idler pulley with this deck. I did have the bearings go out on the added idler pulley and ended up replacing both idler pulleys (this year?). Both idlers were new stens replacements in 2017. I also still had issues with both belts slipping on the center drive pulley even with my modifications but only in thick deep grass. After one bad mowing I had black dust all over the deck and mule drive. The main drive belt was toast and the internal drive belt had signs of slipping. I replaced the center drive spindle with a RM38 drive spindle (faster speed) and now neither belt slips. My 16HP vanguard just looses RPMs now when in deep grass. My outer spindles are also pitted. One slips more than the other causing the blades to drift in and out of sync every few seconds. I just bought replacements from Bob but haven't installed them yet. I've also had issues with the internal tensioner bracket bushing wearing out and seizing to the bracket. I've replaced it twice and the last time I drilled out the bracket and used a beefier spare bushing I had laying around from the mule drive.
20170705_204451.jpg
20170705_204501.jpg

End ramble

Make sure you have adequate tension on the internal tensioner spring. I'm also not a fan of the factory RM48 drive belts. Every one I've bought from various vendors was old dried out rubber. I'm happy with the Gates High Power 2 belts I am using.

Yes, I figure I would get some pushback either for the insult to the divinity of the original engineer. Or for the hubris to think that I can do better.

And I am all in favor of brand loyalty. And I certainly have never seen any brand of lawn tractor that I like as much as a Case / Ingersoll.

But my loyalty to basic physics surpasses my loyalty to the brand



Bob

[thebuildist]

Nice work, Matt. It looks real clean when you're done.

My hesitation to go that route stems from the fact that I'd have to track down a whole extra part, the idler pulley.

And because that idler pulley is now in the tension path of the belt, as opposed to the slack side of the belt, that idler is going to be subjected to greater stress on the bearing than you would normally expect an idler to experience. So the bearings in that static idler are going to have to be replaced more often.

But your well done and easy to follow post reminds me that I should post the same in the process. Complete with the diagram and measurements in case other people want to follow.

Bob