Belt Tensioner

[dale farley]

I turned on my aux air compressor this evening to air up the belts before starting the engine. The compressor pumped to 90+ lbs and shut off as it should. My belt tensioner never aired up. What is the most likely cause? It's been over a month since I started the engine, but I don't ever remember this happening before.

[Gil_J]

Dumb question, your aux compressor is connected to Prevost aux, right?

If so, I would look at protection valve mounted on the Prevost Aux tank in the direction of the aux water seperator in the lower driver's bay. This valve opens when there's about 60psi on either side of the valve.

[dale farley]

Gil,

I assume the answer to your question is "yes". Not sure I know where the valve is that you are referring to, and I do realize I'm not providing much helpful info.

[Joe Camper]

Was the tensioner limp before u turned on the key? Even if there is aux air pressure the tensioner wont air up till key on.

[dale farley]

The tensioner was limp before I turned the key on. Actually, I don't think I turned the key on after I turned the compressor on. I'm pretty sure my compressor will run without the key being on.

I just went and turned the key on, and nothing happened to the tensioner. After I come back from church, I will try draining the aux system down a little, turning the key on and see what happens.

[Gil_J]

Hmmm. There are changes that Prevost made on how the air systems operate and some converters even made changes on the Prevost side. On my 98 chassis, the engine bags received any time the Prevost Aux system had air regardless of the position of the ignition switch.

Dale the location of the converter tie point to the Prevost Aux system is in the driver's bay. From the factory it is labeled. Some converters tied the 2 aux systems together, others did not, while others did but left the valve closed unless their aux compressor died.

[dale farley]

I tried tracing the air line from the tensioner to its source, but I lost it when it went under the bus.

I looked in the front compartment and found a tag that says "Converter". It appears to be between a junction of several air lines and a one way check valve. If you look in the middle of either picture, you can see a small black tie strap. The tie is attached to a tag that says Converter. The check valve is under the junction block.

[Gil_J]

Okay, are you saying the check valve is the first device on the converter side of the manifold. If so, I would assume the check valve allows Prevost aux to flow to converter aux systems. Otherwise converter air systems would only function with the aux compressor running. That would also mean the aux compressor could not inflate the engine bags.

I'm only making an assumption based on my understanding of the converter aux air interface.

FWIW, there is logic to support what each converter did with thier interface to the Prevost aux system and their own. That doesn't mean their logic was the best logic, so some changes can be safely made. I'm not suggesting you make a change, just that your use of the air systems may not be the same as what the converter intended. Again, I may not fully understand your coach's aux air interface.

[dale farley]

I'm still not sure how my system is supposed to be working. Does everyone else have the ability to air up their belts via their aux air system without starting the engine? If so, surely mine "should" be that way also. With the three different buses I've owned, I never had the belts to come off even if I didn't air them up prior to starting the engine.

[Gil_J]

Some Marathon owners report the valve is closed between their aux compressor and Prevost aux air. They are instructed to only open the valve if their aux compressor fails. Do you have a HWH auto leveling controller? If so, the converter aux and Prevost aux would need to be connected.

[dale farley]

I don't have the HWH system.

[Joe Camper]

Dale start the bus and air it up. When it is aired turn it off and go to the back. With the bus off release the belts with the red regulator switch in the engine compartment, and then turn it back on. The belts should not have the ability to reair unless u turn the key back on.

That's how my chassis was and that was done by prevo not the converter.

If your aux compressor will not air up the bags before extended storage it shouldn't matter cause when u turn the key on those solonoids open and thats when they tighten.

That 1 way valve keeps air from going back thru the aux compressor and out its air intake not to isolate the converter aux air and prevo aux air.

[Mike Lentine]

Dale,

I am not sure if you have started your engine since you started this thread but you may find that it doesn't tighten up even after starting the engine. This happened to me a few years ago. It turned out to be the metal braided air line that goes from the valve above the rear engine doors to the tensioner. Water had collected at the bottom of the loop near the crankshaft pulley and rusted shut.

I replaced the hose and all was good.

[dale farley]

Joe,

I finally got around to checking the tensioner again. When I drain the belts with the red valve and then turn it back on, the belts immediately tighten. The ignition switch does not affect the operation of the air to the tensioner. I don't know if that means anything or if it is just the way the converter designed the system to operate. I have about concluded that on this bus, the aux air never aired up the tensioner.

Mike, Mine does air up with the engine, but thanks for the post. You never know when you might have the answer.