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  1. #1

    Default Broken Shear Bolt...

    Hi all,

    My rotary cutter just boke the shear bolt (near the gearbox of the cutter) I cannot find the broken one so I am not sure what to be looking for. I have been searching online for the things but they dont seem to exist. Can I just stick a standard bolt and nut in there? If not where do I find these shear pins or bolts.
    BTW-my rotary is an old Ford (510 I think). I know it is Ford but the numbers behind it are gone.

    Thanks in advance for your help.

  2. #2
    Gold Member
    Join Date
    Sep 2003
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    255

    Default Re: Broken Shear Bolt...

    I just use a standard non-hardened bolt, because that is what was in it originally. It seems to shear anytime I hit a big hidden rock or log, but I guess that's what it's there for. I would start with a standard bolt first, and if that shears too easily, move up to a grade 5 if you need to, but I wouldn't start with that. Mine uses a 7/16" bolt, so I didn't want to use something too strong, and risk busting the gear box.

  3. #3
    Platinum Member Stef's Avatar
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    Mar 2005
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    673
    Location
    South Quebec, Canada
    Tractor
    Kubota B3030 TLB, TYM 330

    Default Re: Broken Shear Bolt...

    Usually shear bolts are grade 5.

    For instance: the shear on the PTO shaft for my snowblower is a 1/4" bolt 2 1/2" long grade 5.

    Last winter I broke one and I went to my dealer. I thought it was a special bolt of some kind but he told me not to worry about it, it's a standard bolt grade 5. So next time, I'll go to the hardware store and I'll pay half the price asked at my dealer.
    Stef

  4. #4
    Elite Member WayneB's Avatar
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    Oct 2006
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    2,788
    Location
    New Hampshire
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    Kubota B-7500

    Default Re: Broken Shear Bolt...

    On my Woods snowblower it is a 5/16 x 1" bolt and Woods recommends a grade 8 bolt but I use a grade 5. Would rather replace bolts and not mess up the PTO or blower. Works for me and I bought my first ones from the dealer and paid a higher price.

  5. #5

    Default Re: Broken Shear Bolt...

    That is good news that I can use a standard bolt!!
    My next question is how do I know what "grade" it is. I went to my local TSC and asked what "grade" the bolts were. I got a blank stare and a shoulder shrug. Needless to say I didn't buy one yet.
    Should there be somthing stamped on the bolt? Also, does it matter if the bolt will be fully threaded?

    Thanks for your help!!

    Lidge

  6. #6
    Silver Member Stoweski's Avatar
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    Feb 2006
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    122
    Location
    Altamont, NY
    Tractor
    Kubota B3200 Kubota RTV900

    Default Re: Broken Shear Bolt...

    Quote Originally Posted by Lidger
    That is good news that I can use a standard bolt!!
    My next question is how do I know what "grade" it is. I went to my local TSC and asked what "grade" the bolts were. I got a blank stare and a shoulder shrug. Needless to say I didn't buy one yet.
    Should there be somthing stamped on the bolt? Also, does it matter if the bolt will be fully threaded?

    Thanks for your help!!

    Lidge

    Hi Lidger,

    Check out this site...
    Bolt Grades

    I went through six bolts on my snowblower this year. At $1.75 each it gets rather pricey. I was wondering if I could use a regular bolt. The only problem I see is that on the original shear bolt there are two grooves in it... probably where the shaft meets the bolt. Not sure if thats important... I'm guessing it is.

    Keith
    Kubota B7610
    Kubota RTV 900

  7. #7
    Super Member
    Join Date
    Feb 2006
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    8,411
    Location
    VA
    Tractor
    JD2010, Kubota3450,2550, Mahindra 7520 w FEL w Skid Steer QC w/Tilt Tatch, & BH, BX1500

    Default Re: Broken Shear Bolt...

    Quote Originally Posted by Stoweski
    Hi Lidger,

    Check out this site...
    Bolt Grades

    I went through six bolts on my snowblower this year. At $1.75 each it gets rather pricey. I was wondering if I could use a regular bolt. The only problem I see is that on the original shear bolt there are two grooves in it... probably where the shaft meets the bolt. Not sure if thats important... I'm guessing it is.

    Keith
    Its important - those reduced bolt sections are the shear points. Get some all thread gr5s from mcmaster carr. The thread grooves will provide natural shear points without having to pay the premium for a modified bolt. Youll probably have to buy 25, but much cheaper per item and useful for many other bolting applications.
    larry

  8. #8
    Elite Member WayneB's Avatar
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    Oct 2006
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    Location
    New Hampshire
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    Kubota B-7500

    Default Re: Broken Shear Bolt...

    Quote Originally Posted by SPYDERLK
    Its important - those reduced bolt sections are the shear points. Get some all thread gr5s from mcmaster carr. The thread grooves will provide natural shear points without having to pay the premium for a modified bolt. Youll probably have to buy 25, but much cheaper per item and useful for many other bolting applications.
    larry
    Larry is absolutely right! You just want to be careful about the softness of the bolt and bolt size. It is best to use a softer bolt and have it brake than go harder and have something else brake. On my Woods snowblower I called the company and they told me to use a grade 8 bolt and I should be okay (just saying I should be okay I decided to go lighter Grade 5)! My kubota parts guy also looked it up and said grade 8 and he added if you are worried about it protect the tractor and go with a grade 5. Bottom line is I would rather go through changing out shear bolts then replacing PTO drives.

  9. #9

    Default Re: Broken Shear Bolt...

    Thanks for your help everybody!!

    I picked some up from TSC today per all your advice. You cant beat paying for those nuts and bolts by the pound!!

    Lidge

  10. #10
    Silver Member simonmeridew's Avatar
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    Sep 2005
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    243
    Location
    Northeastern Vermont
    Tractor
    Kubota L4400

    Default Re: Broken Shear Bolt...

    to determine grade of a bolt, look at the end you put the wrench on:
    Grade 8 has six lines arranged radially
    Grade 5 has three lines arranged radially
    Grade 1 has no lines.

    On my Bush Hog finish mower (5 foot, 3 blades) I use a grade 8 bolt, it's 3/8 X 2 1/2 inches. I put it through the holes connecting the shaft and the PTO assembly(you have to turn it around some to get it to line up) then I put on one of those nuts with the nylon inserts and it will stay put till the cows come home, or until the bolt shears through and it falls off somewhere. Last summer I didn't shear any off, some summers a couple. I figured out that when I raise the mower high with the lift arms, the pto shaft has to do some serious shifting of direction, that is, it isn't a straight shot from the back of the tractor to the mower; because there's a lot of momentum in the rotation of the blades(inertia) and because there's no CV joint, there's a lot of jerking as the tractor tries to turn at a constant rate but the pto, and its u-joints, varies in its rpm depending on which point in its rotation it's at. Sorry that's a long convoluted sentence but it happens when the mower is high. If I don't keep the mower high, I don't break shear bolts.
    I'd use grade 8, because you don't want the thing shearing off every time it encounters a couple of thorn apples trees you're trying to cut off.
    simonmeridew

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