Reason for a VERY loose fan/alt belt??

JRobyn · Apr 30, 2015

Hi guys. Just did the 500hr service on the L4330. The fan/alternator belt was VERY loose! As in I probably could have popped it off the fan pulley with just hand pressure. It has never been loose before and has never been adjusted before. There was only the factory-original clamp mark on the alternator adjustment slot/arm. The alternator pivot bolt was VERY tight. All the pulleys look normal and everything turns freely. The belt is not cracked or frayed and looks almost like new. Tightened it up (adjustment is almost out to the max on the arm/slot now) and everything runs normally.

What could possibly make the belt loosen so dramatically?

- Jay

davesl708 · Apr 30, 2015

New belts will wear into the sheaves over time and the belt will wear down and stretch a little. If the belt is in good shape snug it up as the manual recommends and you will be good to go for a long time.

flyerdan · Apr 30, 2015

Only two things can cause a loose belt: excessive wear (stretching) or the component mounting bolts loosen. It's normal for a new belt to stretch a bit as it wears in, but not to the extent that you describe. If snugging it up takes all the adjustment, maybe you got a defective belt.
Also, check to make sure it is the correct belt, it might be for a different pulley width. While they will fit, a smaller cross section belt will quickly ride much lower in the pulley than normal resulting in a quite loose condition. It could have came from the factory with the wrong belt, mistakes do happen, as the spate of recent car recalls attest.

firemech · Apr 30, 2015

Could it have been that the belt stretched and then started wearing exccessively without squealing or being noticed. If the belt comes loose and starts to slip; it doesn't take long to wear. I hate to admit it but as I get older and 38 years of fire truck sirens in ones ear. I do not readily hear some tones, such as a slipping fan belt

AStanton · Apr 30, 2015

Because it's not much money, I would have an extra fan belt on hand, just in case. You don't want to be in the lower forty and have that sucker let go on a Sunday afternoon. And, as they said in Young Frankenstein, it could be raining.

big bubba · Apr 30, 2015

imho you're just fine w/what you did, all part of the break in process. in terms of getting a spare for now...well, your choice. after all, you're not on the freeway. by noticing it was loose means you're on top of maintenance & just go with it. just keep checking your gauges in operation & an eye to detail & you'll be just fine. good job

2458n · Apr 30, 2015

Might have been alittle loose to start with and with the extra slapping it just got to the point it is now. Good catch.Get the extra belt and you will be ready if this one lets go. If you buy one it will never be needed.

Baby Grand · May 1, 2015

Sounds like that belt is running on borrowed time.
My advice is to get the replacement belt now, so you don't have to fall prey to Murphy's 9th Law:
9. Given the most inappropriate time for something to go wrong, that's
when it will occur.

JRobyn · May 1, 2015

Whatever happened was totally between the 400hr and 500hr service. It was NOT a new belt (factory original), and was snug at 400hrs. I know new belts will stretch just a bit, but this was not new, and I've never heard of one suddenly stretching a bunch after 400hrs of use!

My only conclusion is that some of the cord structure inside the belt is suddenly degrading, but I would think that there would be SOME visible evidence of this on the belt, or something that could be felt. There is neither.

I agree that a spare will be very worthwhile. Anyone know what a standard L4330 (non A/C) fan/alternator belt cross-references to in a regular Gates belt? I assume that an OEM Kubota replacement is excessively priced!

- Jay

flyerdan · May 1, 2015

From what I can find, you should have an OEM belt # 15469-97010 which cross references to a Gates 9425HD. Putting either of these numbers into Google shopping should give scads of results. As always when shopping online be sure to include the shipping costs in your comparisons as a lot of low cost sellers (especially on ebay) roger you mercilessly on shipping to make up for their low merchandise prices.
Often items like this can be bought locally for the same or less, if you're willing to accept a good cross referenced substitute over OEM brand.