John Deere 350 sickle mower breaks cup on Knife Head

[pdreed]

I recently purchased a 350 mower and knife head cup was broken. Welded it and it broke so I bought a complete knife with knife head cup. Used for about 2 hours today an d it broke. Inspecting the gear drive where arm attaches to cutter bar knife, I noticed that there appears to be a good deal of wiggle in bar with counter balance. Is this normal or should the arm be fairly tight when operating? The cover plate over housing does not seem to be to hard to remove to inspect further or am I dreaming.
 

[Tx Jim]

That mower knife head is the same as some of JD's Mo-Co's. Any type wear or looseness will cause knife head to break from the slack. On Mo-Co's slack in the splines where arm(parts key #33A) fit on wobble box was the problem. I realize that 33A is built different than Mo-Co's arm but the principle is the same IE knife head changing directions at a high rate of speed. I would also inspect needle brg(parts key #28) for wear(looseness). Also the knife drive head pin could also be worn.

 

[pdreed]

Thank you so much. I'll get into wobble box and check it further. Needle bearings are new and well lubricated, and shaft from pulley seems to be good and tight so apparently the problem is just with the arm. I'll let you know when I am able to get to it. Am thru with cutting now so may be a while. Thanks again.
 

[gbs]

neighbors 25 foot header got to where it was snapping cutter bars right often at a cost of 900 each, after he had to replace the wobble box problem went away there was to much lost motion in the wobble box causing a shock load effect
 

[pdreed]

Tx Jim: Another question please. After looking at the parts breakdown page, I was intending on getting to the problem by first removing the Drive Head cover to get to the cutter bar and check the bearings. A friend, who was a JD mechanic, offered to help me and he advised that I remove the skid plate and sickle bar and start from the bottom. I'm not a mechanic but have done various repairs etc and would appreciate your comments on way to get to the shaft, etc. BTW, I misread your comments about the needle bearing. I see the one you were referring to. I was referring to the one in the cup. Thanks again for your help. God Bless.
 

[Tx Jim]

Sorry I have no experience on the correct dis-assembly as there were none of those mowers sold at the dealership I worked for. All the help I can be is looking up the parts.
 

[James Howell]

The John Deere Technical Manual TM-1076 illustrates how to remove and repair the mower drive case.

Remove the sub sole from the inner shoe and check the four cap screws ( bolts ) that secure the cutter bar.



Checked the cap screws on our 350 mower yesterday and discovered that all four were broken.





This may have caused the knife head to break on our mower a couple of weeks ago.

Make sure the cap screws are tight and not broken.

Hope this helps.
 

[pdreed]

Thank you very much. I had tried to find a shop manual but had been unable to locate. I will order one from the link you gave. There is plenty of time for me to work on the mower since I am through mowing for this season.
I have never used a forum before and am pleased to find so many kind and helpful people. You folks are wonderful. God bless you for your kindness and may His Grace be multiplied to you.
 

[Dweitzel]

Place the cutter bar down flat, keep hands out of the way and hand turn the belt keeping an eye on the bearing cup and the counter weight. Both pieces should travel in a flat horizontal plane from side to side. I would expect that the bearing cup is being deflected at the beginning of the stroke and the end. The bearings in the wobble box of mine were doing the same when purchased. The deflection caused on the bearing cup would fatigue the metal and snap it after very short usage. The only fix I could see is to take it to a JD dealer. Hope the lower cast part of the wobble box is good. That is around $700 if memory serves me. The wobble shaft is around $2500. If you see deflection, have the JD dealer refurbish the wobble box and you should be good for a LONG time. Just keep grease in all fittings. If you have a machine shop, bearing presses you may be able to do the work yourself. Please let us know what you find.
 

[pdreed]

Thanks for the additional information. It will be a while before I get into the wobble box. However, if the cost approachs the figures mentioned, ---there will be a 350 for sale for parts. A blessed day to everyone.
 

[pdreed]

Thanks everyone. I am in process of putting back together but the problem was in wobble box. The shaft and bearings at center of cutter bar (parts from Diagram #25 & #29) were shot. Parts cost less than $150.00. Should be good to go after get heavy parts back on. (Bar & Knives).
All of your helpful comments and information is appreciatee.
Merry Christmas to all.