Shear Pins

[Piperflyer]

I broke a shear pin that is part of the drive shaft off of the pto drive shaft going to my snowblower(3 pt hitch). I really don't think it was strong enough. I know I didn't hit anything or grind anything up other than light snow. My question is are there different grades of shear pins where I could use a stronger one & what grade would I ask for if there is? Thanks

 

[shvl73]

I would call the manufacturer and get some new ones. In the mean time, soft grade 2 bolts could be an acceptable substitute.

 

[BackwoodsMan]

I have had a similar experience with snow blower shear pins. I think there is a gradual fatigue that occurs. Over time the cumulative affect of ice chunks and other heavy loads weaken the pin and then suddenly a piece of ice creates a drag and the pin shears. If you put a new pin in it should last awhile. In a pinch I have used a low grade bolt, ie., no raised markings on the top (60 KSI). This eventually sheared without any damage to the blower, so I think it was close to the shear pin strength.

 

[DMW]

The first time I used a new snowblower on my then new tractor I sheared the pin 3 times in an hour of use. I found lowering the snowblower to the ground( to reduce the angle of the driveshaft) and engaging the pto at idle reduced a lot of the shock to the pin. ( I haven't had a sheared pin in over a year now) New parts in the snowblower wearing in for the first time could have also contributed to it. It's a pain to replace, always seems to be dark and extremely cold when it breaks ,but, I would rather replace a pin then worry about my tractor's pto driveline.

 

[MadReferee]

The shear pin on the PTO shaft that came with my Puma snowblower is a grade 5 metric bolt. The owners manual specifically calls for a grade 5 bolt here and another on the auger. I have found that the PTO shear bolt will break before the auger shear bolt will. I shear 3-4 bolts per season, most of which are caused by chunks of ice from the town road plowing or short sticks from the trees getting stuck between the auger and fan.

I also tried a grade 2 bolt and it broke under almost no load. The best advice I can give is FOLLOW THE MANUFACTURERS INSTRUCTIONS. What works on my snowblower may or may not work on yours.

 

[KubotaTerry]

I have a relatively new 5' JRW 3pt snow blower. I bought it a month ago and its already got about 20 hours on it. One storm after another here in Colorado....

It uses a 6mm grade 8.8 bolt on the PTO shaft for the shear bolt. I have broken about 8 of them in 20 hours. None of them from hitting anything other than snow. Some of the snow was really solidly packed from being drifted in and then settled for a few days. If I try to take too big of a bite at once, the shear bolt will break. On "normal" snow (whatever that is), they seem to hold up just fine no matter how deep the drift (even over the top of the blower). On some snow, I have to take it easy and go pretty slow to prevent breaking the bolt. Sometimes they also seem to break for no particular reason. I think they just suffer from fatigue. I broke one just from releasing the clutch with the engine RPMs too high.

Luckily, the bolts are cheap and pretty easy to change. It's tempting to up the grade of the bolt, but I'd rather just keep replacing a cheap bolt than risk damaging something more substantial.

Terry

 

[shaley]

Terry, not to be picky here, but I see a lot of confusion when people talk about metric fasteners. In metric bolts, a grade is called a “property class.” A property class designation consists of two numbers separated by a decimal point. The number before the decimal point is one-hundredth of the nominal tensile strength of the bolt in newtons per square millimeter.
The number after the decimal point is the ratio between the nominal yield stress and the nominal tensile strength, times ten.
Bolts in property classes 4.6, 5.6, and 8.8 and above must have the property class marked on the head of the bolt. Property class 6.8 roughly corresponds to SAE grade 2; 8.8 to SAE 5; and 10.9 to SAE 8.
People will think you are using a grade 8 bolt in your snow blower.

 

[KubotaTerry]

Terry, not to be picky here, but I see a lot of confusion when people talk about metric fasteners. In metric bolts, a grade is called a “property class.” A property class designation consists of two numbers separated by a decimal point. The number before the decimal point is one-hundredth of the nominal tensile strength of the bolt in newtons per square millimeter.
The number after the decimal point is the ratio between the nominal yield stress and the nominal tensile strength, times ten.
Bolts in property classes 4.6, 5.6, and 8.8 and above must have the property class marked on the head of the bolt. Property class 6.8 roughly corresponds to SAE grade 2; 8.8 to SAE 5; and 10.9 to SAE 8.
People will think you are using a grade 8 bolt in your snow blower.

Thanks for the explaination. I was wondering what the 8.8 meant. I've just been carefull to use the same thing.

Terry

 

[Soundguy]

I agree with the others.. only use the size and grade bolt that the manufacturer recomends. it may be a pain changing them every now and then.. but it is probably cheaper and easier than changing a gear box and paying for it...

Soundguy