RC2072 Broken Shear Bolt
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Thread: RC2072 Broken Shear Bolt

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    RC2072 Broken Shear Bolt

    Had been mowing for 45 minutes and my RC2072 just stopped cutting. The “shear” bolt connecting the pto to the gear box had broke without me noticing. I am certain I didn’t hit anything (at least not today), and I am also 70% sure my slip clutch is in working order. The mower is 4 yrs old. Has anyone else ever had this bolt break? I found the broken bolt on the mower, there are 6 diagonal lines on the hex head. As mentioned, I do have a slip clutch. I spun the drive shaft on the gear box with a screw driver and it spun freely.
    4066R open station

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    johnH123's Avatar
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    I though I was the only one. I had that same thing happen on my woods BB60x. I went to tractor supply and got 5 new grade 8 bolts and nylock nuts. I installed one and kept 4 for spares. I would also make sure that once you put in the new bolt you slip the clutch and make sure to adjust it to spec.
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    Shear bolts should be grade 2 or 5.....

    Looking for trouble with an 8



    Theres lots of arguments/thoughts on this...I prefer the softer of all options..

    Dan


    JD 955 ,70A loader, 60" mmm , Original I-match ,4' woods B hog , 5' Box blade , 12' orchard plane/driveway grader ,various other doo-dads & homebuilt implements. Goossen BFBlower, JakeRake..this thing is different.
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    Quote Originally Posted by DeereBoots View Post
    Had been mowing for 45 minutes and my RC2072 just stopped cutting. The “shear” bolt connecting the pto to the gear box had broke without me noticing. I am certain I didn’t hit anything (at least not today), and I am also 70% sure my slip clutch is in working order. The mower is 4 yrs old. Has anyone else ever had this bolt break? I found the broken bolt on the mower, there are 6 diagonal lines on the hex head. As mentioned, I do have a slip clutch. I spun the drive shaft on the gear box with a screw driver and it spun freely.
    yes that has happened to me. I think the shear bolt over time is work hardened making it brittle and they eventually just break.
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    Quote Originally Posted by johnH123 View Post
    I though I was the only one. I had that same thing happen on my woods BB60x. I went to tractor supply and got 5 new grade 8 bolts and nylock nuts. I installed one and kept 4 for spares. I would also make sure that once you put in the new bolt you slip the clutch and make sure to adjust it to spec.
    grade 8???? You should use a a grade 3 that's what i have always used. I want the bolt to break like its supposed to not my tractor or implement. Your using a bolt tougher than any part of your implement or tractor, not a good idea. A grade 2 is rated at 64000 pounds per square inch and a grade 8 is i think has a tensile strength of 150,000 p psi!

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    Quote Originally Posted by johnH123 View Post
    I though I was the only one. I had that same thing happen on my woods BB60x. I went to tractor supply and got 5 new grade 8 bolts and nylock nuts. I installed one and kept 4 for spares. I would also make sure that once you put in the new bolt you slip the clutch and make sure to adjust it to spec.
    you wont need any spares
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    my shear bolt just broke too. but it lasted 12 summers-so...............i can't complain a bit-as i've tried to cut sawmill timber with itover the yrs.

    everytime i see the commercial on tv for state farm insurance--where Sheryl's she shed is on fire-i think of a shear bolti just get a kick out of it.
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    Quote Originally Posted by theduke View Post
    Shear bolts should be grade 2 or 5.....

    Looking for trouble with an 8



    Theres lots of arguments/thoughts on this...I prefer the softer of all options..


    That's the point though. if it has a slip clutch you want the 'shear bolt' (its really just a bolt that transmits power from the slip clutch to the gearbox input in this case) to be as hard as possible so that the clutch is slipping instead of bolts breaking.

    Quote Originally Posted by bfloyd4445 View Post
    grade 8???? You should use a a grade 3 that's what i have always used. I want the bolt to break like its supposed to not my tractor or implement. Your using a bolt tougher than any part of your implement or tractor, not a good idea. A grade 2 is rated at 64000 pounds per square inch and a grade 8 is i think has a tensile strength of 150,000 p psi!
    At what PSI is the clutch going to slip at? if its adjusted right and isn't froze up it will do its job and slip if/when you hit something. it doesn't even matter because the original was a grade 8 anyway;
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    Last edited by johnH123; 06-28-2019 at 09:23 PM.
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    - Farm Star rear bale spear

    Yamaha Rhino 700, Yamaha Rhino 660,
    Murray 624 mower/38" deck

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    Mine has no clutch.......


    I can understand your thoughts but have to wonder why there is a bolt. It should have been or could have been a splined connection at the gear box with the quick disconnect like the pto end.

    I've only seen a couple of these on rototillers.....great idea so you can store the driveline/clutch assembly in the shop & out of the rain.
    Grade 8 still sounds painfull to even consider it shearing...
    JD4044M likes this.
    Dan


    JD 955 ,70A loader, 60" mmm , Original I-match ,4' woods B hog , 5' Box blade , 12' orchard plane/driveway grader ,various other doo-dads & homebuilt implements. Goossen BFBlower, JakeRake..this thing is different.
    Kubota U-15
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    Thanks for all the input. I am hoping the bolt broke due to fatigue over the past four years. But, to be safe, I bought two new bolts. One is a grade 5, and I will put that in first. The other is grade 8, same as what was originally installed. If there is something wrong with the gearbox (unlikely as it spins easily by hand), the grade 5 bolt will break more easily than the grade 8 bolt.

    As far as the slip clutch, I last slipped it in May, 2018. But, I have occasionally used a sharpie to mark the two clutch plates. The marks show that the plates move slightly during use, usually when I engage the pto. The clutch doesn’t get hot while mowing either so it is not too loose.
    rtgt, theduke and JD4044M like this.
    4066R open station

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