[Larry & Diane]

The question still remains as to why the belts came off. After start we typically run at idle for 2 minutes to give the accessory air system time to build pressure. If you click fast idle too soon you may run the risk of throwing a belt. Aside from this I suppose misalignement of your sheaves could cause a belt to be thrown, but within a degree sheaves can be quite forgiving.

[Archived]

This may start a discussion in which airing up the aux system prior to start is needed so we won’t throw belts.

I will disagree with that and suggest as David states slight misalignment of the pulleys is a likely contributor. But there is another cause that we have no control over and that is debris kicked up from the road. The most common over the years has been the triple belt that drives the fan box. Originally that set of three belts was a three V belt with the sections joined to make a single belt. I have experienced and seen other instances where something managed to get bounced or kicked up from the road and it got between the belt(s) and the pulley. On the joined three belts the resulkt was usually a nasty tear between two oif the sections and damage or breakage to one or more of the belts.

So far I have not had any belts jump off or get damaged with the thre individual belts, and I suspect that is because most debris kicked up is gravel or small stomes, and if a piece does somehow get between the belt and pulley it goes out between the belts with little or no damage, Something large like a bolt however is going to create a problem although with the plastic panel I now have that fills the gap between the frame and the engine it is unlikely a belt issue is going to be caused by road hazards.

If you disagree with me and air up your coach so the belts are tight prior to starting the engine, tell me how seated coaches do that, since they don’t have aux compressors.

[Archived]

Don’t have the answer on the seated coaches, but I always air up the aux prior to starting. Why would you not air up the aux, it’s a matter of pushing the aux air switch. I have had the belts come off because of no or low aux air, so my routine is to build aux air either with the aux compressor or shop air and I don’t start unless I have checked to be sure the belts are tight.

It’s just one small item to add to your pre-start list. You do have a pre-start list, right? Mine is a walk around checking the following:

1. Awnings locked

2. Visual tire/wheel inspection (I push buttons for pressure)

3. Engine compartment – belts tight, oil, coolant and a visual of components

4. Bay doors all closed/tight and antenna down.

Just for fun, with no aux air, start your bus from the rear (be safe) and watch the belts flopping around. You’ll be using your aux compressor going forward.

[Archived]

Good tip about the spare belts, Peter. That is one of the first things my entertainer bus friends told me when I bought the bus. Having spare belts is cheap insurance out on the road, insurance that I have used in the middle of no where west Texas.

Although it was probably not Peter’s problem since he was already cruising down the highway (Plus, Peter’s aux air probably holds for months) I do subscribe to the practice of letting my air build up before turning the bus on high idle.I was told this by drivers and bus guys that I respect and it was confirmed by Prevost Nashville and by Jeff. I have now driven this bus nearly 100,000 miles so I am pretty sure everything is within tolerance as far as pulley’s lining up, but when I crank the engine with aux pressure down the belts are very loose and I could see how they could easily fly off if the engine was placed on high idle immediately.

I let it run until the aux air rises in about 2-3 minutes and then switch it to high idle. I do not use the aux compressor for this. My old beast needs to warm up several minutes before I drive off anyway. Since I am rarely in a campground, idling is not usually a problem.

So I guess I do respectfully disagree, Jon.

Davy

[Charles]

How did I know this discussion was going to take place?

Tom is right in that airing up the belts stops them from flopping around. If you are going to do as he suggests to get the benefit of air in the aux system wait about 15 seconds after turning the key on before you hit the starter. Air to the belts is blocked with a “key on” solenoid valve on some coaches and you need to give some time to get the valve open, and then for the air to fill the small belt tensioning bellows.

[Sid]

For those that wonder why the belts broke , Gravel or a rock came up took out the one over the road belt it then flopped around and broke one of the three fan gear box belts , it only broke one belt on the fan gear box but the other four had nicks in them

This happened after three hours of starting the drive they where fixing the road where water took out road gravel on it

Jon do you have plastic on both sides ????? mine has it on drivers side but not on the the other that’s how the rock got in to take out the over the road belt then the others , I have video camera back in engine comp I can see what’s going on going down the road

It took a little bit to pull over and get stopped when I saw what was going on

[Davy]

I only have the plastic baffle on the driver’s side.

As stated above road debris is typically why belts get damaged or come loose. I think on coaches with the baffles between the frame and engine rely heavily on those baffles to increase air flow through the CAC and radiator and the side benefit is they cut down on the amount of belt damage due to road debris.

Tightening the belts prior to engaging the starter is another topic because if a belt gets thown when the engine starts it is an immediate issue, not related to road debris.

[Archived]

Tom,

Saw your pre-trip check list. I think you are missing one important check and it can be the last on your list. 5. Nancy on Board. I say it can be last since if first Nancy would have lots of time to change her mind and depart the bus without your knowing it.

[Archived]

Hello Gentleman,

First, I have to ask, why do the belts not stay tight? Our current coach has never had a problem with loose belts. In fact, we only have one large serpentine belt but I know we are talking about a whole different beast.

I know I will learn the starting procedure once the new coach arrives. There is a ‘jack-rabbit’ switch on the dash to increase idle, so, I would have to wait 15 seconds for the air to build before hitting the switch? Does the aux tank always lose pressure when the engine is turned off or will it hold pressure for a couple of days?

It just seems odd that the belts could come off under normal operation.

Mark

[Archived]

Simple answer to your question MM. If there are no air leaks the belts stay tight.

Finding loose belts after sitting idle was cured with the help of soapy water and some cash. Heat is the enemy in the engine compartment as hot operating temps shorten the life of some parts. With your bus being new probably no loose belts for many years.

Serpentine belts are great with far less failures then regular “V” belts. In the Prevost world they are kept tight by mini air bags with regulated pressure, usually 45 psi. The second method is a belt tensioner with spring tension kept constant. The test for belt tensioners is not seeing any shake during its operation. If it’s jumping or shaking that tensioner should be replaced. Life of a tensioner is about 100K miles. But that’s just a rule of thumb. Another check is the sealed pulley on the tensioner should be checked at 50K miles. No noise or roughness when hand spinning the bearing.

[Archived]

Good point on the key for aux, my Liberty had to have the key on to fill the belt bellows from aux, but the Marathon does not.

Will, are you causing trouble again?

[Robert]

The way our coaches are built requires a means of adjusting belt tension and the method chosen was miniature air bags. The engine “floats” on its mounts so the serpentine belt with a tensioner makes sense because that belt drives pulleys that move with the engine. But if we didn’t have the adjustable tension provided by the air bags the fixed gear box for the fan drive or the fixed positioning of the AC compressor would suffer from varying tension as the motor rocks compared to the frame mounted fan and AC.

[Darrell]

Tom, of course not. I’m just working to keep you from getting in trouble!

[Archived]

everytime i come on the PC forums, there is one more thing to freak me out!

actually belts has been on my list for some time. i actually check my engine compartment at pretty much every stop. one reason is to make sure all belts are still there. the fan gear box belts and otr air belts seem to have a little “flop”all the time, but the main belt is always tight. i even have gone as far as put sticky notes on the steering wheel when i switch the belt dump valve off. that and i alwYs make sure the aux compressor is on before starting as well as let the system “cycle” before cranking the engine (turn key part way and let the gauges go through their cycle, then turn all the way).

not sure if that enough time to air the belt airbags,it before i even sit down, i check tension on the triple and double belts as part of my pre-start check.

[Archived]

Jon I have tried the 3A74 (3 wide in one piece) belts and took them off.

I watched them run for a while at idle rpm and the fan gear box bounced too much with them.

When running at fast idle it was much smoother, I know I don’t idle much at low RPM but just thought some times I will forget to hit the fast idle switch and did not like the idea of them bouncing around back there.

Has any one had any problem with the 3 wide belt configurations.