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I was mowing after I had replaced the spindles, blades, and 1/3 idler pulleys ( they mowed freely and were in good condition and didn’t have replacements), engaged blades and the engine bogged a bit (even at high rpm) and the whole mower shook like crazy until it built up rpm, then it just shook a little bit. 10 seconds later, BANG from under deck. The belt had come off somewhere and caused a tangled mess and A keeper turned 180 degrees and bent, it looks like in the photo below. It is keeping the belt on an idler pulley. I’m clueless as to what caused both of these things to happen, maybe the belt is too small or is stretched. This is on a craftsman dgs6500 (2008 917.28848X) with a 54” deck with a Kohler courage sv-735-0016 26HP vtwin. TIA for help

One problem that model number is coming with 48" deck spec'd. So apparently someone has swapped the decks or Sears has the wrong info.


So now we got figure off what the deck came from.

The issue arises due to wear in various components both on the tractor and the deck which leads to that pulley being at too acute of an angle. When the deck is engaged the belt jumps from the sudden motion from the electric clutch engagement. Also on rough yards the belt can also start bouncing causing the same issue. That jump causes the belt to snag between the belt guide and the top of the pulley causing it to pull the guide out of place, jumping off of the pulley, and in some cases damages the belt. That issue has been seen several times over the years on the 54 inch decks used on the Husqvarna and the Craftsman mower they use to make.

I've noticed that:
As above and also any time a PTO is en-gauged and it does not sound right, like you mention, engine pulls down, you feel vibs in your cheeks in the seat, and it's getting worse, then stuff hits the fan, next time think about turning off the PTO before it gets worse because things usually do not get smoother.
I suspect the belt/belts was not routed correctly.

That also can be a dangerous thing to bystanders if a blade comes flying out.

Stay safe when inspecting.
You may have to completely remove the deck for inspection.

I would bet lunch the belt was routed wrong around a belt keeper. Just sayin'

Now I see where there is some confusion with vendors. Some idiot at Craftsman reuse the model number. It is list both for the 48" and 54" decks.

If it has spring loaded idler to tension the belt i would think a belt installed wrong would be evident ?

I’m pretty sure the belt is routed correctly. I did it twice the same way. Second time lasted a bit longer because I moved the keeper a little bit more towards the front of the mower. It’s the exact same setup as in the diagram below and I’m pretty sure the belt was routed as shown, but I’ll try a third time I guess. I will also take that keeper off and see if that fixes it.

SeniorCitizen said:

If it has spring loaded idler to tension the belt i would think a belt installed wrong would be evident ?

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Yes it has a releasable handle connected to a spring that tensions it, will try to reroute belt again tomorrow.

Most of that style deck from husqvarna has a hole in the idler arm where the bottom of that belt guide is suppose to fit into to help prevent it from turning Just be aware that if the belt catches that guide it will bend the guide and pull on from its hole.

And reading the first post it kinda sounds like the OP also has engine problems. I had under powered engine to cause bad deck engagements.

StarTech said:

And reading the first post it kinda sounds like the OP also has engine problems. I had under powered engine to cause bad deck engagements.

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Before installing a third belt, take some time and thoroughly inspect the deck. Look at the level and angle of belt as it is routed. Remove deck if needed . Double check everything closely. As stated previously, ensure belt guide is in correct spot. Initially engage deck at lower RPM and watch, feel, and listen. Stop blades quickly if anything is not right.

ILENGINE said:

Most of that style deck from husqvarna has a hole in the idler arm where the bottom of that belt guide is suppose to fit into to help prevent it from turning Just be aware that if the belt catches that guide it will bend the guide and pull on from its hole.

Click to expand...

That’s what happened the first time. The next time I moved it out of the hole forward 2”

Tiger Small Engine said:

Before installing a third belt, take some time and thoroughly inspect the deck. Look at the level and angle of belt as it is routed. Remove deck if needed . Double check everything closely. As stated previously, ensure belt guide is in correct spot. Initially engage deck at lower RPM and watch, feel, and listen. Stop blades quickly if anything is not right.

Click to expand...

It’s the same belt I have been using, haven’t replaced Until I know that’s the problem

Tried again after I fixed the tangled belt, and it worked even at idle pretty good for about 5 minutes , I throttle up about halfway, let off brake and as soon as I started going BANG…and it happened again Will order new Kevlar belt and will update soon

Get a helper to run the mower for you
Drop the deck to the lowest position on the grass in an out of the way spot
Get them to start the mower then engage the blades while you watch or better still video the belts FROM THE LEFT SIDE
Then go inside and have a couple of beers while you step through the video frame by frame to see where & when the belt takes flight.
I have a Go-Pro ( SJ cam Actually ) with a clamp on mount that I make videos of the deck with whenI have one of these belt problems .

Tried again today (don’t have new belt yet) and worked like last time, came off second I moved forward. This time it didn’t make an exploding noise, just flopped off the PTO and all the other pulley that don’t have keepers. So I put it back on easily and happened again only on the PTO pulley, btw this it electric clutch. So I will proceed and buy a new belt because the old one may be stretched and with the tensioner in place, it is a little loose. Does the PTO need a keeper? It has one to keep it from spinning, but none other than that. Thanks

the pulley grooves could be grabbing the belt / getting a factory belt or known good aftermarket recommended / new spindles move smoothly / recommend new idler pulleys / recheck all nuts & bolts tight /

MechanicLane said:

Tried again today (don’t have new belt yet) and worked like last time, came off second I moved forward. This time it didn’t make an exploding noise, just flopped off the PTO and all the other pulley that don’t have keepers. So I put it back on easily and happened again only on the PTO pulley, btw this it electric clutch. So I will proceed and buy a new belt because the old one may be stretched and with the tensioner in place, it is a little loose. Does the PTO need a keeper? It has one to keep it from spinning, but none other than that. Thanks

Click to expand...

Just an aside notation: A belt doesn't actually "stretch", but rather wears from the "V" side and therefore gets loose from aforementioned reason. My son had anLT 1042 Cub Cadet (MTD) that did almost the same thing. Put it away in the fall, working fine, but the next spring it kept throwing the belt. New belt was no help, so after trying everything I knew, away it went down the road.

Shaking like you stated right after doing spindles could be a blade or spindle pully is not mounted properly

kjonxx said:

Shaking like you stated right after doing spindles could be a blade or spindle pully is not mounted properly

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Good point. Make sure the pulleys are offset in the correct direction so the belt runs in a straight line.

MechanicLane said:

Tried again after I fixed the tangled belt, and it worked even at idle pretty good for about 5 minutes , I throttle up about halfway, let off brake and as soon as I started going BANG…and it happened again Will order new Kevlar belt and will update soon

Click to expand...

Are you saying that the problem happens when you start moving forward but not when sitting still?

MechanicLane said:

I was mowing after I had replaced the spindles, blades, and 1/3 idler pulleys ( they mowed freely and were in good condition and didn’t have replacements), engaged blades and the engine bogged a bit (even at high rpm) and the whole mower shook like crazy until it built up rpm, then it just shook a little bit. 10 seconds later, BANG from under deck. The belt had come off somewhere and caused a tangled mess and A keeper turned 180 degrees and bent, it looks like in the photo below. It is keeping the belt on an idler pulley. I’m clueless as to what caused both of these things to happen, maybe the belt is too small or is stretched. This is on a craftsman dgs6500 (2008 917.28848X) with a 54” deck with a Kohler courage sv-735-0016 26HP vtwin. TIA for help

Click to expand...

I've often found that if I can work on items of this nature that getting them up on a bench, unattached to the tractor is easiest. As I've aged this helps even more. The 60" on the 430 is too heavy to lift alone so I use the cherry picker.

Where are you getting belts? Stick to OEM. I have had cheap ones snap first time or very soon.

It took 18 replies before someone suggested blade balance/installation causing the vibration?

Here's a suggestion:

Take the deck off the tractor and elevate it, if for no other reason than more comfort. Remove the blades, remove the belt completely, and if possible, remove the blade safety brakes so that the spindles can spin freely. Turn each one independently by hand to verify that 1) there is no noise, 2) there is no 'slop' or slack, 3) the pulleys do not wobble on the shaft, 4) the shafts do not have any axial run-out (wobble because they're bent). Inspect the blade end of each spindle to make sure that the blades have not spun on the spindles. That is usually very obvious on both the blades and spindles. If there are zerk (grease) fittings on the spindle housings, pump 'em full of grease until you see it ooze out at either the top or bottom bearing. If it's on the spindle shaft, same goes. Some have the zerks on the spindle shaft, and I highly recommend avoiding those. There's a lot less metal in the spindle shaft (because of the grease galley) and they will break off much easier, typically between the pulley nut threads and splines. An impact (stump/rock) will cause the belt to snap the pulley right off where the greaseless ones or the ones with the zerks in the housing hold up much better.

Verify all idler pulleys turn freely and make no bearing noise. Check all tensioner (idler) springs to verify none is damaged or broken. If you find no suspect bearings, springs, or shafts, reassemble the deck, but do not yet re-install the blades.

Install the deck under the tractor, and run it 'no-load' sans blades to check for noise and belt lash. You'll be able to hear all mechanical noises from the deck drive system, or better yet, hear nothing other than the engine when you engage the PTO. Have someone video the drive belts for you to look at, or maybe borrow a camera you can stick on the deck. Some belt lash is completely normal because they run at relatively low tension and all internal combustion engines have a pulsating torque. Most of the lashing will be on one side which is where the tensioning idlers typically are.

If you are noise and vibration free at this point, re-install the blades. Hopefully you have a mower jack so you don't have to pull the deck again. First, check the balance of each blade. You can do this with a string with a nail tied in it. Just lift the blade with the string. If it tilts to one side, it's heavy on that side. Taking a little more steel off by sharpening typically helps. Mount the blades and make sure that the blades are properly seated on any keying on the spindle shafts, and flat on the flange. Normally if the blade is keyed to the spindle there is a cup shaped spacer or bell washer to keep it on the splines. Make absolutely sure the blade does not turn on the splines while you are tightening it. I find running the bolt in by hand rather than impact works better. Impact is fine for taking up the slack, but do not tighten that bolt with an impact. There is usually a torque specification in your mower's literature, somewhere. Turn the blades (LH and center, then RH and center) to align the tips pointing at the other spindle. Verify the blade tips are very closely matched. Turn both 180 degrees, and check again. If there is a difference in the way the tips meet, you have a bent blade or bent arbor. A slight misalignment could be deck shape tolerance. Check both sides against the center blade this way. If you don't find any significant misalignment, the deck should not vibrate significantly. If it does, then the problem is blade balance. If you have more than one blade out of balance, you'll hear/feel a low frequency harmonic vibration that is speed related. You may get some vibration if the blade tips are passing close as well, but nothing to worry about. The shorter the blades, the faster they have to turn to keep tip speed up enough to move the cut grass. That's one of the disadvantages of a 3-blade deck. I have a 46" deck with two blades which runs at a much lower rotational speed. Balance is MUCH more critical with longer blades. Bent is bent, nothing to do for it but replace it.

MechanicLane said:

Yes it has a releasable handle connected to a spring that tensions it, will try to reroute belt again tomorrow.

Click to expand...

Not once but several times when connecting that spring I rerouted it on the wrong side of the belt. In my case engine bogged down severely and I smelled burnt rubber. Now I tension the belt with mower not running and check if there is interferance between the belt and tensioner spring.

I had a similar problem, and a new tension spring was the answer. Can't remember where I found out about it as a possible cause, but it sure fixed the problem.

Kenneth said:

I had a similar problem, and a new tension spring was the answer. Can't remember where I found out about it as a possible cause, but it sure fixed the problem.

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Husq YTH 2454 2007.Same problem. did 3 things to solve.
1) Replace belt as it probably was cut and twisted when it jammed between keeper and pulley edge.
Will now keep trying to jump and jam on you no matter what you do (IMHO), and experience.
2) As above, get new oem tensioner spring, or, as I did, add a 'helper' spring to the original to keep good tension on belt/idler pulleys.
3) This is key. Design of the belt keeper (shown in photo) is terrible. Too much room for belt to get off pulley and bend the keeper up so that belt is able to jump off idler when elec clutch engages, especially if the deck is in lowered position (large down angle on belt resulting in that 'belt jump' on engagement. I bent the horizontal leg of the keeper enough so that the vertical leg extended further thru the hole in the mounting plate, then threaded the end and installed a jam nut from underneath. No more belt excursions in the last 3 years. Went thru 3 belt keepers before this, usually 1st or second mow right after taking out of winter storage.
As an afterthought, check the belt keeper on the mower frame under the elec clutch for damage or missing (?) as a problem here will also introduce 'belt jump'. good luck!

It really shouldn't be rocket science.
Most of the time when a belt gets damaged quickly it is because it is routed improperly or going around the wrong side of a keeper etc or rubbing on something.
You always need to thoroughly inspect the routing and reach underneath and move one or both of the blades by hand to get everything to rotate so you can watch it moving around etc.
THEN if you're not using OEM belts you're wasting your time.
Far too many problems and busted belts in just minutes or belts only lasting short periods of time or not even gripping properly or disengaging properly on ones with a lever PTO have been attributed to non OEM belts so I won't mess with them at all.

A mower was brought to the shop with same problem.The belt was routed wrong.The flat side of the belt was rubbing against a guide.The Kevlar belt was still good.Tough stuff.It would stall when deck was engaged.My guess is a mis-routed belt,based on years of experience.