Mower shear bolts breaking

[monkeybreath]

Well, I am finally able to get to use my tractor and implements after being out of town for a couple of days. I have used the FEL and box blade and post hole digger and all work well. But I have had a problem with my 72" rear rotary mower (72" Gearmore w/KK labels as well). I read manual thoroughly, hooked it up, checked oil and lubed, double checked all connections, adjusted height, and checked all again as this was my first time using this. Then put in neutral and idling with break on, engaged the PTO to test before I pulled out into field to mow, and "pop", the shear bolt broke. I confirmed that the blades would move, (really rusty under there), and then replaced the shear bolt, and started up again and "pop" it broke again. So, stopped working, and will call dealer in the morning when they open. But - any ideas ? By the way when I bought it I was told to get a 5 bolt as a replacement - but only found a 2 and I think an 8, I will keep looking for a 5.

 

[Slamfire]

I broke another one tonight, have been using 1/4 inch stove bolts, cause I had them. I think in my case I'm spinning the blades too fast. With the pto in 1st gear, it dosen't reach 540 rpm, so I run it in second, with the engine turning at 1800 rpm,. I don't know how fast the blades are turning. I know the main bearing on the output side of the gearbox is good, I replaced it myself. Maybe a change to 5/16th bolts will do the trick. /forums/images/graemlins/confused.gif

 

[monkeybreath]

The bolts I have been using are 1/2 by 3 1/2- What I can't understand is why they break before I even attempt to mow anything. Also, not the best design for replacing the shear bolts - seems like there could be a better way - the safety shield completely covers everything so a real bear to get in there and change the shear bolts.

 

[Slamfire]

Learn to love the shield, I took the 2-point hitch base and turned it upside down for a shield. It has kept the shaft from jumping up and smacking me upside the head, whenever a shear pin breaks on the tractor end. /forums/images/graemlins/cool.gif

 

[normde2001]

Why are you using such small bolts? Use bolts that fit the holes, probably 1/2" #2. How do you know your mower won't hit 540 rpm in 1st pto gear. It will at about 2200-2300rpm.

 

[normde2001]

With the pto driveline hooked up and the pto in neutral, can you turn the driveshaft by hand? Everything should turn freely at that point. Possibly your driveshaft is too long and binding up.

 

[DieselD]

What angle is the driveline at when the bolts are shearing. Did you check for the slip axle lenght?Some are long and have to be cut, there too long when raised.
Danny

 

[monkeybreath]

I'll check those items - and discuss with dealer. The drive line came with the mower and the only adjustment I made was to raise the deck at the rear wheel - it was at the lowest of three settings and I set it at the middle adjustment. That appeared to raise the rear deck by about 2". I am not familiar enough with it yet to know that much about it in detail. Read manual thoroughly and proceeded very carefully so a bit disappointed when couldn't get to mowing, but hopefully will be able to resolve it soon. Thanks.

 

[bgott]

I did a days mowing a couple of weeks ago for a guy whose tractor broke down. I broke a stack of shear bolts. I got the time- to- change down to about three minutes flat. That shield is actually pretty easy to get out of the way once you do it a few time. If you look on the shield it has arrows pointing to lock and unlock. Once you figure out how they're doing it ( it ain't as self explanatory as you might think) the shield slides right up the shaft cover and the bolt is exposed. You have to hold the shaft cover and rotate the shield to get it to unlock. Once you figure out this simple proceedure ( I get ate up with the dummies every once in a while, so what? /forums/images/graemlins/tongue.gif) the next trick is to get the broken bolt out of the shaft on the gear box. Line the holes up and dig out a spare hitch pin and use it for a drift. The little bail on the pin serves wonderfully to keep your fingers out of the way of the hammer. As far as your problem with the bolt breaking before you have the pleasure of hitting something, the other guys might be right about the shaft being too long. Then again, if it's too long, how are you sliding it on the splines in the first place? You need to pull the shaft, remove the safety cover, re- install the shaft and move it through it's full range of motion. Don't engage the PTO, that bolt shearing without a shield to catch it would hurt if it hit someone.

 

[Slamfire]

5/16 is the size of the hole, I used the 1/4 inch to save a trip to town, 11 miles. First gear in the pto gear box is good for 470 rpm with the engine running at 2300, 2 gear is good for 7hundred and something, I don't remember exactly.