185 shear bolt on drive line

[Mike H]

Had a failure this morning with the shear bolt at the back of the flywheel on the 185
thinki I might have over tightened the bolt wen I installed the new drive belts this winter
the one piece found was the nut and part of the threaded bolt ,,it broke just inside of the nut.
havent found the rest of the bolt in the snow yet
temp was -6 this am.
the tractor was running[getting warmed up] and I heard a loud pop
any thoughts ?

gota get warmed up before I go back outside to fix

Mike

[Eugene]

Was the tractor stationary when the shear bolt went? If so, I haven't a clue.

[Mike H]

Was the tractor stationary when the shear bolt went? If so, I haven't a clue.

ya just setting still [warnming up ,,getting ready to use] no load on the drive line other than the cold transmission.

ill check tomorrow to make sure the trans isn't stuck

just a weird place for the bolt to break ,,, only used 1/4'' drive scocket set to tighten too.

Mike

[Mike H]

found the bolt [sticking up out of the snow]
its in one piece with 2 threads left on the end.

Mike

[Landreo]

What bolt did you use? That bolt is not a shear bolt, it should be a at least a grade 5 but is likely a grade 8 allen head cap screw. It has to be tight enough to prevent movement, rotation, of the drive shaft to flywheel coupler. If you used a 1/4 inch drive ratchet then it was not tight enough and the vibration and rotational shear force wore the bolt until it broke. The hole in the drive shaft may now also be worn excessively. I have not found any torque specs for that bolt but 25 ft-lbs would be reasonable for a 5/16 grade 8 bolt. It needs to be very tight. I use a 3/8 ratchet with an allen head adapter to get it tight enough. The original is almost all shaft with only a short threaded part. HamiltonBobs sells the bolts but they do not appear to be the correct bolts. McMaster-Carr has bolts that will work and the correct stength but have a longer threaded length. I have used some of the longer bolts from McMaster-Carr to get the correct shoulder lenght and just cut the threaded end to the correct length.

[BigBill]

Everyone I looked at so far has had threads in the working area on the shaft. I feel the bolt should have the threads on the outside of the working area. A custom bolt can be made by buying it with a longer solid bolt body the cut it to fit. Then thread it one thread below the hole where the nut goes. This way it’s not working on the threads. This can also be drill and safety wired too.

[Mike H]

going to write this one off as a defective bolt.
no unusual ware & tear on the body or the hole it goes into.
it was a nice clean break at the bottom of the thread.
the main body of the bolt covered 99% of the contact area.
bought a grade 8 allen long one to support the hole and trimmed the extra threads off.
dropped the new one in today and got some snow removal done.

Mike

[BigBill]

I’m going to look at boltdepot for a replacement that’s solid. I wonder if a piece of Thompson shaft would work. It’s hardened on the outside.

[Landreo]

The original bolt was a 5/16-18 grade 8 allen head with a 1 3/8 inch unthreaded portion and a 5/8 inch threaded portion.

[BigBill]

Your right the solid body of the bolt should be inside the hole not any threads in the hole. The flywheel works on the threads till it eats through the bolt. One of my 154s had threads in the hole. I caught it just in time.

These are awesome cubs too if they were maintained and repaired correctly. Seems to me they were run into the ground.