ZT52HD DECK VIBRATION FIX

[my87csx481]

I am going to try "something". Just not sure exactly what.

Is this more about mass, or rigidity? You mentioned 3/8" thick....but how wide? 3/8 square?

I was thinking I could get some square tube stock, the stuff that has the holes in it already. Maybe 1" square....but I'll have to check clearance (above, and around). But this will weigh significantly less than a 1 x 3/8 x 40 piece of flat stock (I think).

If I went with the shorter (~10") pieces, what about putting a small piece of plastic, or rubber, in between the brace and the deck (just in the middle of the 10" brace)? To force the brace to flex a bit, and put pressure at the center of the 10" length. Is this worth trying? Before drilling the hole, and putting a third bolt in the middle?

I'm really hesitant to drill more holes in the deck (for now). I really miss having access to welders, and milling machines, and lathes (I used to be a machinist).

 

[tbzep]

I made my own custom fit earbuds using a custom molded earplug kit and some decent ear buds. I use plain ear muff type hearing protection over them. I don't here the chute rattle. I don't hear belts rattle (they don't, but I wouldn't hear them if they did). I do hear the engine and PTO a little, but I mostly hear my music without having to turn it up, thanks to doubling the hearing protection. I subscribe to the "out of sight, out of mind" and "ignorance is bliss" theories. :thumbsup:

 

[Bullgoose]

My87, I apologize for not following up on this topic. I have been preoccupied with tractor problems so I have not paid any attention to this thread. I will try to do better. You asked: "Is this more about mass, or rigidity?" My reply is "yes". I apologize for being flippant, but it is truly about the interaction of both influences.

Let's take a hypothetical situation: Remember, there is not one single solution, as we will see by example.

If you put a 30" X 1" X 1/2" solid steel bar on your deck with the 1" being vertical, it may solve the problem even if it only weighs 5 lbs, but it may not. However, you will be more assured of success if the bar weighs 50 lbs. Now, take that same bar, and cut it to 30" X 1/2" x 1/2" and put 100 lbs on it. That may solve the problem as well, but it may not. I know that some of you are saying: "Bullgoose does not know what he is talking about.

I am using extreme examples to show that it is not just one influence or another. As I said in my initial explanation, I do not have the data to analytically measure the frequencies involved, so I just took a reasonable starting place because the materials and the procedure are easy to come by. If the vibration continues, increase one variable or both. Without the data, we are just guessing what the solution is.

As I have written this post, another idea came to mind. I have never done this, but it would stand to reason (to me) that it would work. Take your mower, and power it up to the speed where the vibration occurs. Take a heavy solid weight (maybe a sledgehammer) that can have force applied through the handle to the weight on the head. The sledgehammer definitely has the rigidity because of its' thickness. Take the weight, and set it on the deck at any given spot. If the vibration disappears, you have found a "sweet suppression spot". If it does not go away, press down firmly on the handle (more weight). If no suppression, move to another spot. Try this until you find a point on the deck where the vibration disappears. Remember, when I started this exercise, I assumed that the deck is where the vibration exists. If my idea does not work, then the vibration is generated at some other point on the suspension of the deck.

Try other points on the complete deck assembly inclusive of all contact points they have with the with the deck. This technique should be easy for anyone to try, and it does not cost anything. It sounds to me like the price is about right.

Regards,

 

[my87csx481]

No problem Bullgoose. Life has a habit of getting in the way from time to time. I will be trying the sledge hammer trick this weekend.

My dealer contacted me this past week. They have the "kit" for me. I will also be picking that up tomorrow (doing the install myself, at my request). I'll report back with kit part numbers, if possible. Supposedly it's two kits.

I have been convinced all along (with no supporting info) that if the belt was not flopping around so wildly, the vibration noise would go away. I have spun all my pulleys looking for wobble/run out. All seemed fine. It occurred to me that maybe the thickness of the belt is irregular, causing the flopping. I'll look at that too, when I dig into this over the weekend. I'll only be able to measure the thickness between the two parallel surfaces of the belt though. I do not have a way of capturing the V and measuring from there to the back of the belt. Or do I? I suppose I could set up a dial indicator on the back of the belt, while running it through a pulley. I'll also report back with whatever I find out.

Thanks again to all that have contributed to this thread, and youtube.

 

[my87csx481]

2 part numbers. First one is basically new pulleys, new tensioner arms, and new hardware. Second part number is new discharge chute, new bogie Wheels, and new hardware. I have not installed anything yet.

59116500
79108000

 

[my87csx481]

What a waste of time.

The pulleys and tension arms are dimensionaly the same as the originals. They also weigh the same (within a couple grams of each other), using my kitchen scale. The new pulleys actually had more wobble than the old ones .035-.040" vs .015-.025", as measured with a .0005" dial indicator, on the surfaces the belts ride on, with the pulleys bolted to the shafts they drive. I have a mag base that I stuck to the deck's top surface to hold the indicator.

Measuring the belt thickness of the parallel belt surfaces with a dial caliper, I got between .395 and .420"....but most times, it was .400" (measurements taken every couple inches).

Basically, the spring anchor for the smaller tension arm gets a new bolt, with fuel hose on it, instead of the metal bushing. The bogie wheels get new, larger diameter bolts, with no metal sleeves, and no spring washers. The discharge shoot mounting bracket gets a couple holes drilled through it and the deck, and a couple bolts through the holes.

Perhaps a physics major, or a hardcore mechanical engineer could take the time to explain to me how swapping pulleys and arms of the same dimensions and masses will alter the violent belt vibration? I fail to see how these parts will do anything other than suppress the rattles somewhat. In my case, I've already removed all the guards, chute and bracket....months ago. So I didn't bother installing any of the kit. I'm not sure how I will proceed with this. I am extremely disappointed.

I did try probing the deck with an 8 pound sledge hammer. I could not find a sweet spot. I went as far as standing on the deck (I'm a big guy at 230 pounds). That helped a little, when standing on the left side. I also noticed that the top surface of the deck does vibrate with the oscillation of the belt vibration. I will be adding stiffeners at some point, and I will explore adding another pulley inbetween the PTO and the first pulley (on the left side of the machine....the slack side of the belt).

 

[cpurvis]

I recommend you do some before and after kit installation videos. I know it seems like a waste of time, but I'd install every new component of their kit and if it makes no difference, you'll have video evidence of it.

Let's hear what Bullgoose has to say about it.

 

[Newcombe]

Hi Guys, just to chime in on this thread as I'm contemplating buying a ZT HD 52" in the next couple of weeks. I'm now having second thoughts. I do like the Gravely machine compared to other brands for the money. At this point should I buy the 48" rather than the 52 due to this one sole issue, the 60" would be too big for where I keep it? Any help would be appreciated before I make a $5,000 mistake.

 

[cpurvis]

Try the 52" you intend to buy (the exact unit). If it vibrates, take it back. If it doesn't, buy it but with the understanding in writing that if it starts to vibrate, you want a whole new deck.

If they won't take that deal, pass it up.

 

[Newcombe]

It surely makes me nervous to make the purchase seeing all the issues these fine folks have had with their units. Would the dealer be able to make that decision on replacement of the deck prior to Gravely's approval?