What to do now: No serpentine belt fits...

Bought a 2007 GMC C4500 bus to use as a poor man's toterhome. On the way home from that purchase, the belt shredded itself and I had bus towed to my job site, an hour and some change from home. Since then I've tried:

• The belt listed at the FLAPS (136.xx"). Way short, didn't take into the account that the bus upfit added an AC compressor, idler, and repositioned the tensioner. 
• The belt listed on the sticker from AC upfit. Which should theoretically be dead on (139.5" called for. Bought 140.125" as that was closest I could find). Still obviously short. 
• The next closest I could find going larger. (142"). I could theoretically have pried that belt on if I'd had extra help and lubed it up, but tensioner was 100% maxed and it was still an easy 1/2" from going on. I say that's still short.

Problem I have is that as best I can tell, next commercially made belt is 145.5, which feels like way too big of a jump. It was obviously running a belt when I picked it up and I doubt it was anything custom made, so I'm a little stumped. There are grooves worn into the tensioner where the inside of the belt was riding on the body of the tensioner, which based on the geometry of everything, leads me to believe that they had a belt that was way too loose on there (when tensioner is "at rest", the belt path would rub, right where those grooves are). I don't want to repeat that, but not sure the best path forward. 

Thoughts on how/why/what next:

• Both alternators look to be fancy hi-amp versions that could very easily have different sized pulleys from original install.
• Bolt was "other than factory" holding one of the idlers in place, so they've obviously changed the idlers out at some point. I also replaced 2 of the 3 idlers, just as something simple to do to eliminate a pooched idler bearing as reason it shredded the belt in the first place and both factory idlers that came off matched the factory spec'd idlers I put on. 
• I assume that the power steering pump, fan pulley/water pump, factory AC compressor pulley, crank pulley and tensioner are all the same size as they were when the add-on AC happened during upfit, so if a 139.5x belt fit then, the changes would have to be the alternators. But am I missing something, or maybe that's a bad assumption?
• If I could get idlers of slightly smaller diameter, and belt travel path still cleared obstacles that idlers are bending it around (both definitely "ifs"), then theoretically the 142" belt would fit.
• Alternate option would be bigger idlers, if they make em, if belt clears, etc. and jump up to the 145.xx belt (which is my working assumption as to what was on it). 
• A custom belt.

Appreciate any thoughts. Never thought I'd be stumped on a serpentine belt. I take whole engines out with my bare hands. And sometimes put them back in. And sometimes, some of those run again! A belt can't be where I get defeated. 

How many ribs is the belt?

In reply to No Time :

6. But at this point I guess cutting ribs off an 8 rib should be an option on the table, too. 

Can you get any model or length info from the shreds of the original belt?

My Samurai has a customized accessory belt system and I run a stock-spec belt that's probably too small by "jumping it on." This involves getting the belt almost-installed in a way that cranking the starter will finish the job and pop the belt onto the last remaining pulley. This is a lot easier and less risky with a V-belt vs. a multi-rib belt though. Also removal requires cutting the belt.

GameboyRMH said:

Can you get any model or length info from the shreds of the original belt?

My Samurai has a customized accessory belt system and I run a stock-spec belt that's probably too small by "jumping it on." This involves getting the belt almost-installed in a way that cranking the starter will finish the job and pop the belt onto the last remaining pulley. This is a lot easier and less risky with a V-belt vs. a multi-rib belt though. Also removal requires cutting the belt.

No, she was proper shredded. And I found a sister bus being auctioned at local-ish YMCA and couldn't read anything on that belt either. Only thing I didn't do was try to measure all the various pulleys. Think auction ends tomorrow and I'm out of town (Sonoma for a day with Hyundai track experience!) until Monday, so doubt I'll get to mess with that bus again, unfortunately. 

And I pondered trying to do that, but I suspect it would cut before it jumped on. It really wasn't "close". I had 1 or 2 ribs on the pulley, and the part of the belt that wasn't on the pulley was pretty bent over from the tension, if they makes sense. 

Another thought: if the 142" belt was 0.5" from going on at max tension, that suggests that a 143" belt would be a bare minimum, and the tensioner would have to extend another 1.25" to start tensioning a 145.5", so maybe it's not that excessive?

Is this the 142" you used? Otherwise maybe the 1/2" could be enough to get you going?

No Time said:

Is this the 142" you used? Otherwise maybe the 1/2" could be enough to get you going?

Used the Dayco interchange. Both 142.0x effective length, 142.5x outside circumference.

So. Not that belt, but theoretically that exact length. 

Gates lets  you search idler pulleys by diameter, and from there you can refine by bearing size, etc: https://www.gates.com/us/en/power-transmission/power-transmission-components/idler-pulleys.html

I used this myself both to save weight w/plastic pulleys over steel and also to fine-tune belt fitment, as you're doing.

Will said:

Gates lets  you search idler pulleys by diameter, and from there you can refine by bearing size, etc: https://www.gates.com/us/en/power-transmission/power-transmission-components/idler-pulleys.html

I used this myself both to save weight w/plastic pulleys over steel and also to fine-tune belt fitment, as you're doing.

Thanks! If inflight WiFi allows, might give me something to do this afternoon.

Are you sure you're putting the belt on correctly? I had a car where there were 3 ways you could put on the belt. Only one way was long enough and correct, the last way I tried.

VolvoHeretic said:

Are you sure you're putting the belt on correctly? I had a car where there were 3 ways you could put on the belt. Only one way was long enough and correct, the last way I tried.

I'm sure I'm matching the diagram on the sticker from the add-on AC compressor, which matches the running bus the Y is auctioning. So, I *think* yes. Not really a ton of options to screw it up and still put grooves to grooves and smooth to smooth.

I just went back and was looking at the original thread about the belt to look at the diagram.

Is the diagram wrong, or does the alternator on the upper drivers side have an adjustment slot? Maybe that could be modified to get a little more adjustment?

I assume you've already experimented with all the available adjustments - the "add-on B/S idler" looks to have a bit of sideways adjustment slot, plus the upper right alternator mounting bracket. You could also move the add - on compressor in and out on it's mounting bolts by using different spacers/washers, that might get you the adjustment you need.

But Jeebus, $99 freaking dollars (!) for an accessory belt? It better be made out gold-plated Kevlar infused with carbon fiber, and have a lifetime guarantee. YOUR lifetime, not the belt's.     

No Time said:

I just went back and was looking at the original thread about the belt to look at the diagram.

Is the diagram wrong, or does the alternator on the upper drivers side have an adjustment slot? Maybe that could be modified to get a little more adjustment?

I think they used some semi-generic graphics. Don't think either alternator is adjustable for tension. Here's a pic of the sister bus's drivers side alternator. Assume mine to be identical.

earlybroncoguy1 said:

I assume you've already experimented with all the available adjustments - the "add-on B/S idler" looks to have a bit of sideways adjustment slot, plus the upper right alternator mounting bracket. You could also move the add - on compressor in and out on it's mounting bolts by using different spacers/washers, that might get you the adjustment you need.

But Jeebus, $99 freaking dollars (!) for an accessory belt? It better be made out gold-plated Kevlar infused with carbon fiber, and have a lifetime guarantee. YOUR lifetime, not the belt's.     

Have not looked at ability to move add-on idler. And that could be all I need, if it has any degree of movement. I did consider that some shorter spacers and maybe bolts would move the 2nd AC compressor closer without consequence, but this thing is broken down at my job site, which is over an hour from home, so simplest solution (in terms of both time and ease of implementation, but also acknowledging that I've only got whatever I bring with me from home) is the goal.

Spearfishin said:

Problem I have is that as best I can tell, next commercially made belt is 145.5, which feels like way too big of a jump. It was obviously running a belt when I picked it up and I doubt it was anything custom made, so I'm a little stumped. There are grooves worn into the tensioner where the inside of the belt was riding on the body of the tensioner, which based on the geometry of everything, leads me to believe that they had a belt that was way too loose on there (when tensioner is "at rest", the belt path would rub, right where those grooves are). I don't want to repeat that, but not sure the best path forward.

It might not be the correct solution, but I imagine this would work to make it the last hour home where you would have the time and equipment to figure out a long term solution.

dps214 said:

Spearfishin said:

Problem I have is that as best I can tell, next commercially made belt is 145.5, which feels like way too big of a jump. It was obviously running a belt when I picked it up and I doubt it was anything custom made, so I'm a little stumped. There are grooves worn into the tensioner where the inside of the belt was riding on the body of the tensioner, which based on the geometry of everything, leads me to believe that they had a belt that was way too loose on there (when tensioner is "at rest", the belt path would rub, right where those grooves are). I don't want to repeat that, but not sure the best path forward.

It might not be the correct solution, but I imagine this would work to make it the last hour home where you would have the time and equipment to figure out a long term solution.

As mentioned above by earlybroncoguy1, these belts aren't cheap. If I buy and run it, I want that belt to be the solution. In an ideal world, anyway. 

Have you thought about pulling a string around the belt path and measuring it?  (Making allowances for the tensioners, etc.)

triumph7 said:

Have you thought about pulling a string around the belt path and measuring it?  (Making allowances for the tensioners, etc.)

My first thaught as well. Then Amazon and get the one closest to your measurements and get one longer and one shorter than your measurements. Return the two you don't use.  

This is the part number on the sticker?

https://www.coachbusparts.com/part.php?id=996

Edit: Oops it's NLA. Looking some more....

From the description:   # of Ribs on Belt: 6
Belt Length: 139.58 in.
Belt Top Width: .84 in.

Cross ref:

https://www.coachbusparts.com/comparison.php?cat=1&subcat=35

Given the remote location, I think I'd unbolt/loosen the most easily accessible item the belt's route, install the slightly-too-short belt, and use the mounting belts for that item to tighten it in-place. I would not mess with the tensioner as they can sometimes be a real bear to deal with.

NermalSnert (Forum Supporter) said:

This is the part number on the sticker?

https://www.coachbusparts.com/part.php?id=996

Edit: Oops it's NLA. Looking some more....

From the description:   # of Ribs on Belt: 6
Belt Length: 139.58 in.
Belt Top Width: .84 in.

 

Cross ref:

https://www.coachbusparts.com/comparison.php?cat=1&subcat=35

That's where I started this journey was with a 140" belt. Something funky is going on, and it doesn't fit. 

kb58 said:

Given the remote location, I think I'd unbolt/loosen the most easily accessible item the belt's route, install the slightly-too-short belt, and use the mounting belts for that item to tighten it in-place. I would not mess with the tensioner as they can sometimes be a real bear to deal with.

I gave some thought to that Wednesday. Could probably slack up the alternator bolts, get belt on and "tension" it with the alternator. What's the risk of having a belt that's pulled banjo string tight?

And is there a way to quote more than one post in a single reply?

Dumb question: have you confirmed that the tensioner is still fully functional and not stuck in one position?