Bobcat drive belt tensioner failure

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skidsteer.ca

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I got a eye opener this evening the belt on my 773 began to slip so I went to tighten the main hyd pump drive belt. I pryed the idler pulley back down to wind up the spring and though I was all set.
I fired it up and it immediately tossed 2/3 of the belt of the pulleys.
Now I've learned I should have added geasing th bushing in the excentric of the idler to my 400 or 500 hour service. The following pics tell the story. The only good parts are the idler wheel, tensioner spring, a few washers and the dust cap.
With 2000 hours on this machine, sevice is way past due.
I guess I'm going to get a new idler assembly and belt tomorrow.
IMG_0467.JPG

Remove the dust cover with a cold chisel
IMG_0470.JPG

Lossen the 3/8 bolt and remove the stack of washers and spring.
IMG_0474.JPG

You can see how the one side of the bushing is completely gone (to the left side of the center hole, and whats left of the bronze bushing on the rh side of the center hole) and the center of the excentric is all worn out. The hole is supposed to be in the lower rh of the center hub. Now it has almost worn to the center. The roll pin holes are all wore out too
IMG_0475.JPG

This is the back side. 1/2 of the seal is completely worn away
IMG_0476.JPG

The shaft is worn where the seal would run
IMG_0477.JPG

Again only 1/2 of the bronze bushing left on the rh side, and note how the top roll pin hole is worn away.
 

Tazza

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That uum... pretty bad!!!!
Still, i wouldn't have thought it would fail in 2,000 hours of use, those bearings are all sealed.
 

Tazza

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That uum... pretty bad!!!!
Still, i wouldn't have thought it would fail in 2,000 hours of use, those bearings are all sealed.
Now that i did a few calculations, thats probably about rite. Most cars require a major service for changing timing belts and idlers at 100,000 K's, and working on an average of say 70k's/hr thats 1,400 hrs or close enough to it.
It looks like you got a pretty good life out of it.
I hope the new idler isn't too costly, and more importantly you don't have to wait too long for a new one.
 

siduramaxde

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Now that i did a few calculations, thats probably about rite. Most cars require a major service for changing timing belts and idlers at 100,000 K's, and working on an average of say 70k's/hr thats 1,400 hrs or close enough to it.
It looks like you got a pretty good life out of it.
I hope the new idler isn't too costly, and more importantly you don't have to wait too long for a new one.
Does every Bobcat have that same belt tensioner???
 

skidsteer.ca

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All east/west facing engine models will run an idler like that. All old model ones like 743 and erlier have a direct connection, so no belt.
Actually the bearing has not yet failed, the grease feels stiff, but it may go 500+ hours yet. But I'd change it anyway.
The problem is with the spring loaded self adjuster. uses a spring like a rewind starter. The steel piece in the center of the bearing has the hole drilled offset. And it was bushed with a bronze bushing. The spring get wound up when you pry the idle up against the belt. Then as the belt wears the spring pressure keeps turning the offset to move the idler closer to the belt.
Bobcat used some without this spring, but you had to adjust them more frequently.
This one should have had the bushing changed 500 hours ago and new grease put on the bushing to help it last longer, probably every 500 hours would be a good time to grease and check it.
A complete new idler is $323 cdn and the belt is $58
I may try to repair the old one, but i need to weld up the shaft and turn the seal surface down. The center piece is likely not worth fixing, though I have yet to price it, but boring and re bushing it down would not be easy. and the roll pin holes still need fixed.
Then I need a bronze bushing, a seal and a bearing
So I starting to think it may not save much to repair it
If you loader has the sideways engine in it , you may want to check this on your next service
Ken
 

Team Craig

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Actually the bearing has not yet failed, the grease feels stiff, but it may go 500+ hours yet. But I'd change it anyway.
The problem is with the spring loaded self adjuster. uses a spring like a rewind starter. The steel piece in the center of the bearing has the hole drilled offset. And it was bushed with a bronze bushing. The spring get wound up when you pry the idle up against the belt. Then as the belt wears the spring pressure keeps turning the offset to move the idler closer to the belt.
Bobcat used some without this spring, but you had to adjust them more frequently.
This one should have had the bushing changed 500 hours ago and new grease put on the bushing to help it last longer, probably every 500 hours would be a good time to grease and check it.
A complete new idler is $323 cdn and the belt is $58
I may try to repair the old one, but i need to weld up the shaft and turn the seal surface down. The center piece is likely not worth fixing, though I have yet to price it, but boring and re bushing it down would not be easy. and the roll pin holes still need fixed.
Then I need a bronze bushing, a seal and a bearing
So I starting to think it may not save much to repair it
If you loader has the sideways engine in it , you may want to check this on your next service
Ken
Ok now I am going to have to check mine. Looking at the pictures I am not sure what bushing you are talking about? Was the bearing turning ok/not siezing up? With the amount of dirt these things are subjected to I would think the bearing would not be freely spinning to cause that kind of damage? I ran into this on my 773 with the small belt idler pully. The bearing was completly full of dirt although it was a sealed brg. I see this same thing happen frequently on Motocross bikes I am always working on - Sealed brgs full of dirt and siezed up as a result. I love the information I get on this site. Skidsteer ca and Tazza are a wealth of knowledge - Thanks guys...
 

siduramaxde

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Ok now I am going to have to check mine. Looking at the pictures I am not sure what bushing you are talking about? Was the bearing turning ok/not siezing up? With the amount of dirt these things are subjected to I would think the bearing would not be freely spinning to cause that kind of damage? I ran into this on my 773 with the small belt idler pully. The bearing was completly full of dirt although it was a sealed brg. I see this same thing happen frequently on Motocross bikes I am always working on - Sealed brgs full of dirt and siezed up as a result. I love the information I get on this site. Skidsteer ca and Tazza are a wealth of knowledge - Thanks guys...
Ok, I guess I need to check this on my T200???
What and how exactly do I check??? Is there something to grease???
 

skidsteer.ca

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Ok, I guess I need to check this on my T200???
What and how exactly do I check??? Is there something to grease???
The bottom picture shows 1/2 of the bronze bushing on the rh side of the center hole. The bushing is inside the hub, the bearing is outside the hub, and the idler is outside the bearing.
The bearing was turning fine but the grease in it is getting a little stiff.
The bronze bushing rotates on the shaft everytime the load on the engine changes enough for the belt to stretch a little. It seves the same purpose as the spring loaded tensioner on a serpentine belt drive on you pickup, but istead of the idler being on a arm, the hub is bored offset. That offset rotates on the bushing and shaft and the offset causes the idler to move in to tighten the belt.
The first photo show the “dust cap” , just like a trailer wheel bearing/hub uses. Just take your hammer and cold chisel and pop it up out of the idler. It should be greasy inside this. Mine was full of black dust. If its greasy its fine, maybey put more in and put the cover back on.
To disassemble,put the bracket into your vise remove the 3/8 bolt, then the stack of washers.
At this point you can see the bushing around the steel shaft. If it is wearing thin then this is the time to replace it. It will only wear on the one side that the spring put pressure against. If it is not worn oblong, then either spray it with you favourite lube, or unwind the spring and pull the idler wheel off the shaft. Then you can give it a good coat of grease and re assemble.
Also with the bracket still bolted to the engine but with the belt off, I could grab the idler and rock it side to side 10 to 15 degrees. And when I tighten the belt I could see the idler leaning sideways. I should have never even tried starting the engine because all I did was ruin the belt.
I'll scan my service manual on this and post it here when i get a chance. But if your concerned, just loosen you belt and give it the “rock” test.
I have yet to hunt down my favourite tech, but maybe someone in the know will chime in as to how common this problem is. Maybey I just got a dud.
I know I'll be greaseing mine and checking the bushing play from here on. I ordered a new hub $80 (the part that goes inside the bearing, that the bushing goes into, a new bushing, $10 and new seals $16. And I'll get a bearing from a bearing supply place. And I'll still have to weld up the sureface the inside seal runs on and turn it round again and polish it. So I'm sure I'll have at least another $100 of time into it
Ken
 

Team Craig

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The bottom picture shows 1/2 of the bronze bushing on the rh side of the center hole. The bushing is inside the hub, the bearing is outside the hub, and the idler is outside the bearing.
The bearing was turning fine but the grease in it is getting a little stiff.
The bronze bushing rotates on the shaft everytime the load on the engine changes enough for the belt to stretch a little. It seves the same purpose as the spring loaded tensioner on a serpentine belt drive on you pickup, but istead of the idler being on a arm, the hub is bored offset. That offset rotates on the bushing and shaft and the offset causes the idler to move in to tighten the belt.
The first photo show the “dust cap” , just like a trailer wheel bearing/hub uses. Just take your hammer and cold chisel and pop it up out of the idler. It should be greasy inside this. Mine was full of black dust. If its greasy its fine, maybey put more in and put the cover back on.
To disassemble,put the bracket into your vise remove the 3/8 bolt, then the stack of washers.
At this point you can see the bushing around the steel shaft. If it is wearing thin then this is the time to replace it. It will only wear on the one side that the spring put pressure against. If it is not worn oblong, then either spray it with you favourite lube, or unwind the spring and pull the idler wheel off the shaft. Then you can give it a good coat of grease and re assemble.
Also with the bracket still bolted to the engine but with the belt off, I could grab the idler and rock it side to side 10 to 15 degrees. And when I tighten the belt I could see the idler leaning sideways. I should have never even tried starting the engine because all I did was ruin the belt.
I'll scan my service manual on this and post it here when i get a chance. But if your concerned, just loosen you belt and give it the “rock” test.
I have yet to hunt down my favourite tech, but maybe someone in the know will chime in as to how common this problem is. Maybey I just got a dud.
I know I'll be greaseing mine and checking the bushing play from here on. I ordered a new hub $80 (the part that goes inside the bearing, that the bushing goes into, a new bushing, $10 and new seals $16. And I'll get a bearing from a bearing supply place. And I'll still have to weld up the sureface the inside seal runs on and turn it round again and polish it. So I'm sure I'll have at least another $100 of time into it
Ken
Cool now I understand how it works and what has happened. Sounds simple enough - the only worry is the spring loaded deal. I have never had much luck repl the rope of pull start with the coil spring you mentioned so I hope the spring in this setup is much easier to deal with... Thanks again...
 

skidsteer.ca

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Cool now I understand how it works and what has happened. Sounds simple enough - the only worry is the spring loaded deal. I have never had much luck repl the rope of pull start with the coil spring you mentioned so I hope the spring in this setup is much easier to deal with... Thanks again...
I got my new hub finally and it came complete with the seal and the bushing for $83 cdn.
I welded the seal surface up with the mig and the casting has good steel in it and it welded perfectly. Bolted it up to my lathe and turned it back down, good as new. The seal only slides on this sureface when the excentric rotates to “adjust “ the belt. So it does not have to be “110%” so to speak.
Re asembly went good and the spring is a piece of cake, nothing nearly as ignorant as the rewind springs, you only have to wind it a 1/3 of a turn.
The new 6207 bearing was available from my local bearing supplier for $16. Bearing is held to the hub with a internal and external snap ring so you need some pliers to remove these.
I'll post another pic of the back of the asembly, as you can check how much the bushing is worn by looking at how close the pin is to side of the “curved slot“ in the back of the tightener. This check only requires you remove it from the machine not tear it apart.
I'll be checking mine at 250 hours now, until i see how the grease is lasting. Probably it would be good for 1000 or so.
Ken
 

farmboy55

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Aug 16, 2006
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I got my new hub finally and it came complete with the seal and the bushing for $83 cdn.
I welded the seal surface up with the mig and the casting has good steel in it and it welded perfectly. Bolted it up to my lathe and turned it back down, good as new. The seal only slides on this sureface when the excentric rotates to “adjust “ the belt. So it does not have to be “110%” so to speak.
Re asembly went good and the spring is a piece of cake, nothing nearly as ignorant as the rewind springs, you only have to wind it a 1/3 of a turn.
The new 6207 bearing was available from my local bearing supplier for $16. Bearing is held to the hub with a internal and external snap ring so you need some pliers to remove these.
I'll post another pic of the back of the asembly, as you can check how much the bushing is worn by looking at how close the pin is to side of the “curved slot“ in the back of the tightener. This check only requires you remove it from the machine not tear it apart.
I'll be checking mine at 250 hours now, until i see how the grease is lasting. Probably it would be good for 1000 or so.
Ken
I guess my 853c has the same setup? So in for a ck up, next rainy day..
 

skidsteer.ca

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I guess my 853c has the same setup? So in for a ck up, next rainy day..
Actually my 853 c does not have a spring (it does not self tension) but it uses 2 tapered cone and cup bearing and is filled with 15/50 synthetic motor oil instead of grease. So you won't have the problem I had,(with the bushing) unless yours happens to be update to the spring loaded tightener.
The fellow I had got my 93 753 from said it came factory with a fixed tightener, but he later updated it to a spring one, so I not sure what happened to the first.
I'm going to check the side play of the idler. It should be .005 to .013” and the oil level, also a vary precise quantity .50” deep using the dust cap as a bowl to measure the oil. Exactly 20 cc.
The spring loaded tighteners have a 4 “ or so diameter flat wound spring clearly visable behind the idler wheel. And a curved slot in the back side of the bracket.
Ken
 
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