Shear bolts on 513 cutter

jrdellaratta · Jul 6, 2004

This weekend I blew another two shear bolts on my 513 cutter---this works out to 6 bolts in less than 20 hours of cutting over the past 2 months. Kind of aggravating, especially since some bolts seem to go in very unlikely places: open, flat areas, with not-too-tall grass. The good news is that I've gotten very good at swapping out the bolts; the better news is that I'm seriously considering an MX6 with slip-clutch.

Is it possible I have the cutter set too low, or that the blades are too tightly connected to the stump-jumper and don't have enough "give"?

Dutch445 · Jul 6, 2004

JR,
Are you sure you are replacing with the proper grade of bolt? (hardness)
Also, how low are you cutting? If you are very close to the ground, you could be hitting the ground on and causing the bolts to break. Is the cutter level from front to back? (and side to side i guess also)

RobS · Jul 6, 2004

I broke one the other day, first this year. Over the past couple years I've probably broken five or six total. Are you seeing/hearing it hit things? If so, that could explain it. Mine doesn't seem to mind the rocks as much as the scalping.

Are you using the proper bolt (size and grade)? Not sure what else to tell you but I sure would like to upgrade mine /forums/images/graemlins/smile.gif

beenthere · Jul 6, 2004

( ""Is it possible I have the cutter set too low"" )

There would be a clue to this by just looking at what you are mowing. Are you tearing up ground? Are you into stumps, roots, or rocks? Someone borrowed my rotary cutter (before I had the Deere 513) and it came back with the seals out and the blades destroyed. He said he didn't hit anything in particular. I was later at his place where he was putting trails through his woods. I couldn't believe what he was using my rotary cutter for. He had it down where nothing was left but bare ground. He was using it more like a box blade or a surface tiller. Not saying you are doing that, but if the correct shear bolts are breaking, then there should be indication as to what is causing the problem that you can see.
Do you hear the blades banging around when starting and stopping the cutter? That is when I hear them, knowing they are loose. They shouldn't be stiff, and you can check that by moving them to see if the blades are properly bolted on with a bushing to keep them from being too tight.

Kyle_in_Tex · Jul 6, 2004

I had the same exact situation happening with my 4310/LX5 combo. My dealer has sold me some low grade bolts and self locking nuts. These are the type of nuts that have a plastic ring that keep the nuts from backing off. When installing the nut onto the bolt, just take up the slack, do not overtighten the nuts. (Overtightening stretches the bolts and weakens them.) Also, I had to loosen the slipper clutch all the way to make sure it wasn't froze up between the metal and fibrous clutch material ring. I then experimented with the amount of preload applied to the clutch's bellville spring plate. I ended up having to back each nut back at least 2 full revolutions to where the slipper clutch would slip under the harshest conditions. make sure you adjust all the clutch's nuts the same. Now everything is much better...Kyle

jrdellaratta · Jul 7, 2004

Thanks for the suggestions.

1) What I'm cutting is pretty well-maintained; I usually go after it when it's 8"-12" high. There are spots with stumps, but I know where they are and avoid them. (what my dad does, on his weekend jaunts around the property, I can't speak to)

2) I have the rear of the cutter alot higher than the suggested 1"-2" higher than the front height, mainly becasue I was trying to improve the discharge rate, and keep the cutter from bogging down in any case. Should I make it more level? It's very seldom that I scrape anything, except occassionally the front of the runners.

3) I've been using the 8.8 M10x75 shear bolt as called for in the manual, but I will be careful not to overtighten the lock nut from hereon. What I have is not the plastic type, but the metal one that costs ~$1 (the bolt only costs ~$0.37). I've started a collection, and can proudly saty at this point that I have all three peices of each of the 6 broken bolts. I have no idea what to do with them, but for some reason want to save them.

4) The blades seem to have a decent amont of swing to them, when I push/pull them by hand, but I will say this: with the cutter raised fully, they don't swing forward on their own, like the blades on my BH light-duty 5'er used to (which I'm starting to miss, rugged as it was)

em14 · Jul 8, 2004

I have the 513 and if I am using it on the JD 5220 I carry a sack of shear bolts. I find that most of the bolts are sheared when I forget to ease the engagement of the PTO. The "shock" load from the PTO agnist the stationary blade (not turning) will eat shear bolts like pop corn. On one of the pages in the manual I seem to remember another recommendation for a grade 5 bolt. That's different than what they say in the back of the manual! I don't have the manuals here to check myself but that is what I went to ... If I use the 513 on the JD 790 I seldom shear a bolt ... I keep telling myself that I am going to install an old slip clutch I've got but I need to replace the shafts which are bent. Anyway I don't worry very much about shear bolts on this cutter any more. It works very well and cuts some very heavy brush and 2" plus trees without shearing a bolt ... it's just me forgetting to engage the PTO slowly that's the biggest problem.

RobS · Jul 8, 2004

I find that most of the bolts are sheared when I forget to ease the engagement of the PTO 

Oh yeah, I forgot about that one. I had trouble with that, then my wife had similar troubles. Once we learned to engage the PTO slowly and only at engine idle, we quickly solved that problem /forums/images/graemlins/smile.gif

jrdellaratta · Jul 8, 2004

I've been consistent about engaging the PTO at idle, once I took possession of the unit and poured through the manuals. One question, remains, though: do the shear bolts wear at all, get weakened in any way over time, or do they just snap in an "all or nothing" scenario?

RobS · Jul 8, 2004

do the shear bolts wear at all, get weakened in any way over time, or do they just snap in an "all or nothing" scenario? 

I suspect they do get weakened with "medium" impacts over time and will eventually break with a lesser impact than a fresh bolt would. The one I replaced last week left me with this impression as I hadn't hit anything significant in recent memory.

From an engineering point of view, any load on the bolt that causes deformation will weaken it though it may not be enough to cause ultimate failure. Subsequent loads will further weaken or eventually fail the bolt. The shear bolts are relatively soft steel so they will tend to deform quite a bit before breaking /forums/images/graemlins/smile.gif