busshog shear bolt

[MikeA57]

We broke 2 shear bolts on the bushhog a couple of weeks ago and I went out and bought a half dozen spares to keep on hand. I thought they were 1/2" Grade 2 bolts. When I went to put one of them in last weekend I found out that they are too small to fit through the holes in the yoke although they fit fine through the shaft of the gear box. I'm wondering if anyone can think of a problem with me enlarging the holes in the yoke so the 1/2" bolt will fit all the way through? I'm thinking that since they were obviously smaller than 1/2", when the gear box locked up from hitting something it acted like a cutter on the bolt since it was a larger hole than the bolt going through it.

 

[greg_g]

A rotary cutter - regardless of condition - is worth more than half a dozen GR2 bolts. The answer to the over-bore question depends upon whether the existing holes have gone elliptical. If they're still round, get the right diameter bolt. Using bolts that are too small is what ruins the holes to begin with. So if they're already worn to the point of being elliptical, you can consider boring them out. But it's a death spiral, you'll likely have to do it again - and again. It might be less aggravating to either (a) replace the yokes, or (b) replace the whole PTO shaft.

//greg//

 

[skipmarcy]

Try a 7/16" grade 2 bolt, been running them in my rotary cutter for almost 15 years with not a single problem, a little bit of slop hasn't hurt a thing on mine and I know I have over 1000 hours on mine. No telling how long they were used before I got it used years ago ....

 

[LD1]

The shear bolts are there to protect the bushhog AND tractor from damage.

With the hole in the shaft being smaller than 1/2", that gearbox was obviously designed for a SMALLER shear bolt. The shear strength of a 1/2" bolt is going to be higher than whatever was in there before. And if you go bigger, you risk breaking the next weakest link in the system. Which would likely cost more than even 100 shear bolts. So measure the hole (or test fit with some other bolts) and get the right size.

The yokes being egged out or larger will have little effect. Cause once under load, there isnt really any slop. The slop gets taken up by the driving force. So its not like if you hit something that the yoke has a half-a-hole head start. So it has little effect. The bolt you had broke for a reason. Its cheap and easy to replace. Would you rather be replacing the PTO shaft or gearbox or tractor pto????

 

[Soundguy]

he said the input shaft WAS 1/2" but the yke is smaller.. ? perhaps 7/16 or 3/8 unless I read that wrong.


sounds like a replacement yoke from a smaller mower.

if the holes in the yoke are smaller than the shaft.. I'd bore them out true tothe shaft diameter hole. mind you.. if the youke was for a smaller bolt.. it may be thinner.. and after shearing some 1/2" it will liekly start to go eliptical as it was made to shear smaller bolts.

just keep that in mind that one day instead of a bolt shearing, the yoke may come apart... as someone else said.. it's a spiral at this point.

you can't leave it sloppy.. that's asking for shearing... making it right will wear the yoke..

eventually, down the line.. SOMEthing will need repalcement.

optionally you could BUSH the hole in the shaft if the holes in the yoke are not eliptical.. however.. smaller bolts will shear faster.


any sign that the hole in the input shaft was overbored?

 

[LD1]

Brain fart...I read that backwards. If it is the yokes that are too small, then no I dont see a problem enlarging it. I now understand what you were talking about with the shearing effect. Do yea, drill out the holes or bush the shaft.