I am not using a hard bolt, it might even be grade 2. Bolt does not have any radial markings on the head (ie 3 or 6 lines) but does have a very small 7 imprinted in the center. Galvanized 1/4 x 20, nothing fancy.
I checked the owners manual, and the shear bolt is not a hex head bolt, it is an allen head bolt. The head of the bolt is recessed in the yoke and has a washer and nut on the other end.
Milkman, I didn't have appropriate allen bolts around. I used hex bolts with sufficient non threaded length to pass through the coupled shafts. Again, I'd rather have the shear pin break than other gear train components.
Milkman, I didn't have appropriate allen bolts around. I used hex bolts with sufficient non threaded length to pass through the coupled shafts. Again, I'd rather have the shear pin break than other gear train components.
100% right, but I was replying to Bobg and then clarifying my original post, what I thought was a hex head shoulder bolt is actually an allen head bolt. I understand sometimes you have to go with whatever you got.
Mine has done it about three times, used the Allen head bolts from NAPA that had a shoulder long enough to go through the shaft all the way, the Hillman ones at the hardware store are not long enough. I think the Allen head bolts are at least a grade 5. I think I fixed the problem by grabbing a handfull of the bolts and bringing them home to have spares as it has not done it since.
I have a shear bolt on my rotary cutter. The first hour I had it I backed up over a substantial accumulation of grass (piled and rolled tightly due to incorrect mower adjustment) and broke my first shear bolt.
The mower came with two spares, so I immediately went out and bought five more. I have spent a dozen hours brush hogging heavy saplings and dense vines, but haven't broken another bolt yet. I would not consider moving to a tougher bolt for fear of damaging components.