Craftsman rider Deck vibration issue

[RMR]

I have a Craftsman 917.203810 that a customer brought in with a "deck problem". I discovered both spindles were worn out. I replaced both mandrels, blades and the belt. The idlers are both smooth and tight, so I left them alone. It still has a terrible vibration when the blades are engaged. Both mandrel pulley's spin true and smooth. I ruled out the spring tension by pulling it as tight as possible with a cord by hand while the blades were spinning. Is this a idler arm problem? There is no obvious damage to it, so I hate to just throw parts at it. Below is a video showing the belt slap that's causing the vibration.

[bgsengine]

try running it with blades removed? maybe they out of balance, or not level to each other?

[RMR]

I'll put a second set of blades on it and see what it does. I've done that before and while it did take the vibration away with no blades, it came right back with a whole new set of blades. Because the problem was still there, but it was not amplified because the weight of the blades was gone.

[bgsengine]

yeah but you can generally still see it while watching the belt - belt slap like that can be due to a deformity in pulleys (or excessive paint drip in a spot or some such, on new , painted drive pulleys) or just a bad spot in a belt (Ive seen aftermarket belts and even a couple OEM belts where they are "glued" together, but mis-aligned, causing a "bulge" in one spot of the belt) , check all the pulleys (including PTO drive) for anything like that.. sometimes it can even just be a weak or incorrect idler tension spring.. aftermarket spindles also are not necessarily assembled to the best of tolerances (loose bearings, for example) that won't show up while spinning them by hand but only show up when they have a lateral load (belt tension, blade weight, etc) .. and some decks are just simply poorly engineered , wear tolerances stacked up can translate to as much as a half inch to an inch of "slop" in some places

[38racing]

Could It be that the belt is to long?/

[RMR]

Tried another set of blades, all pulley's are smooth and clean, and the belt looks good and straight. I'm going to try a shorter belt to see what that does. I measured the one that it called for and it is 101 1/2" inches. I think it could easily be a inch shorter with the slack that I see at rest.

[KE4AVB]

Okay I be the first to ask. Was the vibration there before the deck work? As it is sounding like a bent spindle shaft. I don't where you check for blade wobble. I have gotten defective spindle shafts before.

I also see the left hand idler sitting wrong. Very possible the idler bracket and spacer heavily worn. I have replacing quite a few of these idler arms and spacer this year both Husqvarna and MTD decks

[RMR]

I found out that the vibration has been there since he bought it used 3 years ago. The new spindles both spin straight and true under a load. I was able to go all the way down to a 99" belt with plenty of disengagement slack left. Though it did not help the problem at all. The customer said he was not worried about the vibration (he brought it to me because the blades wouldn't stay tight), and needed the mower back. SO I told him to bring it back if he wanted me to look into it any further. I'm sure the vibration isn't helping the blades stay tight and I know it's hard as hell on the bearings. but you can only lead a horse to water......

[bgsengine]

those machines do have a tendency to have harmonic vibrations in the deck , if you can change the vibration by changing engine speed while it is running, then it's probably a harmonic vibration at a specific speed - the main problem with them is just that the deck mounting points are flimsy to begin with so with a used unit, if it runs too long with something bent or out of balance, it wears in a specific spot, so that even after the balance or alignment issue is solved, the vibration will still be there due to the wear spots in linkages - nothing really to do about that other than to replace all the linkages and brackets that have any wear to them. by which time you may as well just buy a new tractor, after paying the parts bill (if parts are even available any more) So, probably just have to live with it - run it til something breaks and get a new one.