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Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: opus on March 21, 2013, 06:59:43 PM

Title: Belt tensioners
Post by: opus on March 21, 2013, 06:59:43 PM
Are these things generic or are there gobs of different ones?


Title: Re: Belt tensioners
Post by: Tony LEE on March 21, 2013, 09:59:55 PM
Lots of different ones - left and right acting too - but they are generally findable on-line by using the words 'belt tensioner' plus the engine designation ie cat 3126 etc
$100 upwards

Title: Re: Belt tensioners
Post by: Tony LEE on March 23, 2013, 02:08:00 PM
Actually, looking at that photo, I'd say the belt is the wrong length.

For that size tensioner, putting a 1/2" drive handle in the square hole, it will take a lot of force to de-tension the belt, but in the photo, looks as if the tensioner is right around on the stops so the belt tension might be quite low.

Maybe not - only check is to see how hard the belt is to deflect midway between a couple of the pulleys

Title: Re: Belt tensioners
Post by: wg4t50 on March 23, 2013, 04:46:57 PM
NAPA stores carry the Gates tensioners, seems they have great replacements for Cummins and a better price, pLus seem to be a bette quality.  I have no experience with the Gates modEl, but talked with users.
Dave M

Title: Re: Belt tensioners
Post by: opus on March 23, 2013, 05:01:58 PM
Found a Gates for $55.  Had to call Cummins to get the right number.  Not sure if thats the right belt or not.  Its been on for quite a while though.

Title: Re: Belt tensioners
Post by: luvrbus on March 23, 2013, 05:14:00 PM
What is the problem with the one you have now bearing replacement is fairly easy on those for under 10 bucks

Title: Re: Belt tensioners
Post by: opus on March 23, 2013, 05:15:45 PM
Nothing.  I am fond of having spares.

Title: Re: Belt tensioners
Post by: Tony LEE on March 23, 2013, 08:57:57 PM
Had to pull the radiator out of my MH on the side of the road in Mexico a couple of weeks ago to change the water pump and also found the tensioner was way below the required value. That explained the occasional squeal when the dash aircon was switched on, but the puzzling thing was how can the tension drop to say a tenth of the spec value unless the spring broke - or some clown put the wrong one in in the past.

Title: Re: Belt tensioners
Post by: rv_safetyman on March 24, 2013, 07:30:47 AM
Both the belt and tensioner are application specific.  The tensioner has a very high spring rate.  When the belt length is correct and the belt has not "stretched", the idler should maintain the proper tension.

These idlers are on the "slack side" of the drive.  In that position, they do not have to maintain a high tension statically.  The spring loaded idler is the secret to making these drives work.  With them the tension in the belt is proportional to the load (you don't want to hear the technical explanation ::) ::) - but I can refer you to an ASAE paper I wrote that gives the engineering explanation ::) ).  Since the belt sees a rather low belt tension over most of its life (only high tension when one or more of the accessories are working hard), it does not stretch and wear very much - thus the high rate spring works fine.

The idlers generally work pretty good for a long time.  Very infrequently they will develop some high internal friction, but most failures are tension spring.  The idler bearing fails once in a while, but that is different from a tensioner failure in my mind.

I say that the tensioner is application specific.  A subsidiary of Gates made tensioners for the automotive OEM market and was a major supplier.  They then designed a tensioner for a Detriot Series 60 engine and had major problems.  When the engine would idle (think of a truck parked over night), the torque pulsations would make the idler dance and caused premature spring failures (think a month or two life).  We set up a brand new Series 60 in our lab and let it idle 24 hours per day.  Finally got a good design.

My guess is that the someone had replaced the belt on the motorhome with an aftermarket belt that was too long.  That let the idler get out of its fairly narrow operating range.

Sorry, tired to avoid replying to this thread, but my geek side would not let me ;D


Title: Re: Belt tensioners
Post by: opus on March 24, 2013, 08:26:51 AM
Everything is fine on the bus.  Was just wanting to gather a spare.  Knowing the guy that owned this prior, I find it hard to believe he put the wrong belt on it.  So you are saying the gap between the idler and water pump should be greater than it is?

Tension on this seems fine.  I havent changed the belt since I have owned it, which would be 3 yrs.  According to the belt gauge there is plenty life left.  Thought I would put new ones on and keep the old for spares.