Fan Belt Tension

[CountingFireflies]

Howdy -

I have an MCI 102C3, and the fan belt tensioner air cylinder started leaking horribly, so I removed it and replaced it with a turnbuckle, which, by the way, I would never have thought of without reading this forum.  Thank you to all that posted about it.  Anyway, now the question is, how to tell if the belt is tight enough?  Currently, with moderate pressure at the vertical center of the belt, I can push it 1-2 inches.  When I start it up, it looks good, but it looks much tighter than when the air actuator was in use.  My thougths are that the actuator wasn't expanding enough and we have probably been running too loose for some time.  Any thoughts?


Thanks.
Chris.

[DMoedave]

Chris, i dont have an MCI but that seems ok. How much belt length are we talking? I have pretty short double belt set up and they seem tight at rest but look "jumpy" with the engine running. I like your "looks good" while running description. Good luck

[CountingFireflies]

The fan belt is about 4' from top to bottom.  It isn't tight like you'd have on a pickup or sedan.  When it's running it's so long that you can see slacking or jumping on the forward side.  I think overall, the point is to keep the fans running, and it seems to me that too tight would cause friction, heat, and premature belt wear.  We definitely were running WAY TOO loose before the fix.

Chris.

[DMoedave]

I wasent sure if your newer MCI had the longer belt setup. I would think youare about right. I have the same issue about making them to tight on mine. i am more concerned about the alt and pully bearings but they are tensioned right at rest and i dont have slipping. I think my issue is the "matched "set is not that well matched. 

[chev49]

The "matched set" on my bus has one with twice as much deflection as the other now. maybe i should switch them, or buy another set. Checked mine when this post first came up. They aren't old.

[Iceni John]

When I asked ABC Bus about buying a matched set of alternator belts to keep as spares, they told me that belts these days don't come as matched sets any more.   They said if I bought two identical belts at the same time they should be matched well enough to work as a matched set.   I don't know if this is true, or if they're blowing smoke, but it's possiible that more stringent QC these days may mean that belts have better consistency than before.   Who knows?

Whatever the story, I'll buy myself another pair to keep as spares.   Even unmatched belts work better than broken belts!

John

[rv_safetyman]

It is true that the manufacturers of INDUSTRIAL belts agreed on what they call the "no match system" - over 20 years ago.  This cover cross sections A/B/C/D and 3V/5V/8V.  More than likely the MCI used "B" section belts.  These belts would be matched within a manufacturer but not between manufacturers.

True automotive belts (as defined by SAE) are not a part of a "no match system" for most manufacturers.

I always used to caution our customers who said that one belt was out of match, as measured by apparent looseness on a span, to be careful of that observation.  Belts always "fight" each other to a minor degree and when you shut them down, they generally tend to have different tensions in each span.  Take a look next time and you will probably see that the loose belt on one span will be the tight belt on the other span.  If it is loose on both spans (by a big margin), then the set should probably be replaced.

I can't recall whether the MCI air tensioner pushed on an idler or pushed on the driven shaft.  If it pushed on an idler, that is a wonderful system that makes the belt tension proportional to the load.  The fan HP variation is huge depending on RPM and to have the belts always be tensioned based on the load is a huge benefit.

Jim

[chev49]

When it stops raining and blowing 40mph i will check that.