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So i recently had no issues with my lawn tractor (5 years old) model number 917.28861 54"deck.
Did a full tune up on the mower.. ran great but then i engaged the blades and there was a lot of knocking and vibration coming from the deck
Finally i realized one of the blades wasnt in the star pattern enough and stripped the mandrel, So i replaced the mandrel recently and put the new blades on.
Engaged the deck and same still a ton of vibration. Checked all the pulleys everything checked out.. i replaced the 5 year old belt figured there was not enough tension.
Engaged the deck.. same vibration.. just maybe a tad less.. Took off the blades.. Engaged the deck.. Vibration.. I honestly cant figure it out? im going under the tractor
again today after spending 12 hours on it yesterday.. to check the main pulley under the motor? maybe that has something to do with it.. im just checking for looseness...
Any help would be great..?

Try checking for "runout," of the spindle shafts by eyeballing or using a wire fastened to something stationary , with the tip held very near shaft. There should not be any wobble. Maybe you bent or damaged a spindle shaft or bearing.

At this point I would remove the cutting deck and give it a THOROUGH inspection. Run the mower WITHOUT
the deck and see if things change ...?? Vibration is caused by movement ( something loose, cracked, vibrating, etc.)
You may have to clean the deck really good to find what may be the cause ..
Finally ...How did you manage 5 years out of a belt ..???

cslix said:

So i recently had no issues with my lawn tractor (5 years old) model number 917.28861 54"deck.
Did a full tune up on the mower.. ran great but then i engaged the blades and there was a lot of knocking and vibration coming from the deck
Finally i realized one of the blades wasnt in the star pattern enough and stripped the mandrel, So i replaced the mandrel recently and put the new blades on.
Engaged the deck and same still a ton of vibration. Checked all the pulleys everything checked out.. i replaced the 5 year old belt figured there was not enough tension.
Engaged the deck.. same vibration.. just maybe a tad less.. Took off the blades.. Engaged the deck.. Vibration.. I honestly cant figure it out? im going under the tractor
again today after spending 12 hours on it yesterday.. to check the main pulley under the motor? maybe that has something to do with it.. im just checking for looseness...
Any help would be great..?

Click to expand...

Here are THREE VIDEOS
https://www.youtube.com/watch?v=OezhslSGbnw

https://www.youtube.com/watch?v=hkAJ_5HnSIA

https://www.youtube.com/watch?v=O51hSaBhmnY

Boobala said:

At this point I would remove the cutting deck and give it a THOROUGH inspection. Run the mower WITHOUT
the deck and see if things change ...?? Vibration is caused by movement ( something loose, cracked, vibrating, etc.)
You may have to clean the deck really good to find what may be the cause ..
Finally ...How did you manage 5 years out of a belt ..???

Click to expand...

To be honest this tractor is my fathers whos 60 that does not believe in preventive manitance and fixing things him self..
So i feel bad and do any work i can for him and look at it as a learning experience.. im the one who replaced the belt other wise there have
never been a new belt.. he also saved the old one lol..

I took the deck off and cleaned everything and replaced the mandrel.. One this i did not mention is two bolts broke in the old mandrel housing so i taped and dyed out the bolts and re threaded
then bought 3 new bolts that fit the thread with washers and replaced it.. the mandrel is snug so im confused.. i dont think this would have thrown it off still? the problem was before i did this and after..

DIDN'T finish your last post..
failed to mention if you ran mower WITHOUT THE DECK ??? ...results ..??
mandrels (spindles) may be tight mounted to the deck ..BUT are the SHAFTS wobbling or bent IN the mandrels
do they rotate smoothly and freely ...??? if not ... could be bearings are shot !!

Boobala said:

DIDN'T finish your last post..
failed to mention if you ran mower WITHOUT THE DECK ??? ...results ..??
mandrels (spindles) may be tight mounted to the deck ..BUT are the SHAFTS wobbling or bent IN the mandrels
do they rotate smoothly and freely ...??? if not ... could be bearings are shot !!

Click to expand...

A lot of people get the mandrel confused i believe? and call it a shaft..? There a mandrel housing.. which i taped and re bolted.. The Actually mandrel is the part that fits between both
bearings and attaches to the blade that spins.. anyway i literally stripped one of the mandrels "shafts" replaced it.. it had i guess a bearing at the bottom? that was new.. also
there was an old bearing that was at the top.. that i did not replace.. but it seemed to spin fine..

So Basically Here it is.. Process of elimination
This Problem started after i did a tune up..
I replaced the plugs.. Checked them they were sam model number as the old..
I replace the air filter.. same.. also ran with out one..
I replace the oil/ and filter, also tightend and tefloned both bolts on the engine block due to oil leaking.
I then replaced the Fuel filter.. the fuel filter looked a little smaller but said it worked in engine up to i believe 29hp or so.. not sure if it was for kholer engine though.
then i replaced the blades.. my father used it and said it didnt feel right at all like it didnt have enough power and the deck was vibrating too much.. his guess was lack of power..
So i realized the mandrel was stripped.. the star shape.. so i took off the old mandrel housing.. broke 2 bolts in it.. Tapped new threads not perfect.. Bought stainless 5/16ths bolts and washers
re attached it and it fit fine and snug.. replaced the with the new mandrel.. old top bearing still in.. put blades on perfect.. Still Vibrationg and struggling..
I then replaced the 5 year old belt with a new one.. that didnt help..

So i have acouple of ideas.. maybe this will help you guys in helping me..
1.Fuel filter? Wrong size? restricting engine power.. not enough power to run the deck correctly..?

2. Since i tapped new threads in the mandrel housing and used different but similar bolts with washers this could actually be throwing it off?

3. top bearing spins fine but is 5 years of age..? doubt this is the problem but someone mentioned it..

4.. the drive pulley, and maybe belt? also maybe the automatic clutch.. i dont know much about these things but in my video theres some side to side blade in the clutch.. belt feels fine but
maybe its super old and worn out?

My questining is that this issue happened after that tune up above.. so it has to be one of those things no?

The 2004 dyt 4000 only recently had its original blade and ground drive belts changed.... Regarding the vibration: bad bearings can appear ok at rest, but be faulty at load. What is the check for "grittiness" when turned by hand? Blade balance ? Did you look at the runout of the spindles?

Just ordered these https://www.amazon.com/gp/product/B00CTYQAU4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
came with two im just gonna install one..
im hoping maybe this will fix the problem..
ive been worried since we tapped new threads and used different bolts.. that maybe this threw everything off.. so im changing them just to rule it out..
55 bucks later.. this mower loves money..

motoman said:

The 2004 dyt 4000 only recently had its original blade and ground drive belts changed.... Regarding the vibration: bad bearings can appear ok at rest, but be faulty at load. What is the check for "grittiness" when turned by hand? Blade balance ? Did you look at the runout of the spindles?

Click to expand...

run out of the spindles??

Just ordered these https://www.amazon.com/gp/product/B00CTYQAU4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
came with two im just gonna install one..
im hoping maybe this will fix the problem..
ive been worried since we tapped new threads and used different bolts.. that maybe this threw everything off.. so im changing them just to rule it out..
55 bucks later.. this mower loves money..

You never stated if you ran the mower WITHOUT the cutting deck ..???
If so what were the results ?? By doing so you determine if the problem is in the deck or in the tractor ...

"Runout" The shaft should turn with no wobble...like a pencil does in your fingers. Any small "runout" is magnified to anything attached to it....the star holding the blade. So the blade of slightly bend spindle shaft (hit something?), or a worn or loose bearing will transmit imbalance from the rpm of the unbalance blade through the deck. This is what happens when you run an unbalanced car wheel. A little problem becomes pounds of force felt through the floor and suspension. You need a way of seeing if the shaft is "true." The wire pointer is poor man's dial indicator. "Dial indicator"...a little gage with a contact point and a pointer showing movement of the shaft, if any.

Also check that the 4 bolts that hold the engine in the mower are tight.
An please answer the previous question so we can work out if it is in the deck or the mower.