Dadnatron
Veteran Member
I just purchased a new flail mower. Straight from China. I ordered it, shipped it in, and put it together.
Everything seems to work normally. Everything turns by hand, but the flail is 84" long with hammers.
The gearbox isn't the biggest one I've seen, but I suspect it should be adequate, at least for some time. However, I am breaking shear bolts upon startup each time I try to get it going.
I can get it started, with the PTO and the machine turning, but long before it spools up to regular power, the shear bolt breaks. The original bolt was a Grade 5 bolt. I went through 3-4 of them again, without success. I decided WTH, and put in a TSC Grade 8 and same thing happened. They are shearing upon startup. Everything moves, and it doesn't appear that anything is bound up. It just seems as though the inertia of getting this thing moving is higher than the strength of even a G8 5/16" bolt.
Overall, the size of the bolt seems pretty small and I wonder if the PTO shaft is undersized for the size of the machine. I measure the U-joint to be 70mm so this would be a Series 3 PTO shaft according to U-joint measurements. Given the PTO requirements rated on the machine and the HP of my tractor, this should be between 70-100hp and a Series 8 PTO shaft. But I see no torque on the shaft (I've removed the cover and have just been trying to make sure everything is up and running before I put it back on.) It moves... the flail drum freely moves and spins for quite a while after the bolt shears. I suspect it gets up to about 40% speed, lasting about 2 sec before the shear pin breaks.
I'm thinking I need to add a slip clutch to the shaft in order to be able to tighten it adequately to make the system work. And while I've used PTO shafts with the clutch already installed, I've never installed one myself.
Any thoughts on this issue? I know the typical is 'something is too tight and it is binding' but I don't think this is it... I think it just takes 'too much power' to get everything up and moving, and by the time that has occurred, the shear bolt has broken.
PS: I am contacting the manufacturer and telling them about the issue. I think, looking at the situation, that they simply included the wrong size PTO shaft for this machine. A Series 3 shaft would be typically with a 20-25hp machine.
If this is the case, and I want to get another 'domestic' PTO shaft, what is the best source for one? I'd like to get one with a CV joint and a slip clutch if possible. Any options on US source? I need 540rpm collapses to 72" between shafts with expansion of about 12-16" it appears.
Everything seems to work normally. Everything turns by hand, but the flail is 84" long with hammers.
The gearbox isn't the biggest one I've seen, but I suspect it should be adequate, at least for some time. However, I am breaking shear bolts upon startup each time I try to get it going.
I can get it started, with the PTO and the machine turning, but long before it spools up to regular power, the shear bolt breaks. The original bolt was a Grade 5 bolt. I went through 3-4 of them again, without success. I decided WTH, and put in a TSC Grade 8 and same thing happened. They are shearing upon startup. Everything moves, and it doesn't appear that anything is bound up. It just seems as though the inertia of getting this thing moving is higher than the strength of even a G8 5/16" bolt.
Overall, the size of the bolt seems pretty small and I wonder if the PTO shaft is undersized for the size of the machine. I measure the U-joint to be 70mm so this would be a Series 3 PTO shaft according to U-joint measurements. Given the PTO requirements rated on the machine and the HP of my tractor, this should be between 70-100hp and a Series 8 PTO shaft. But I see no torque on the shaft (I've removed the cover and have just been trying to make sure everything is up and running before I put it back on.) It moves... the flail drum freely moves and spins for quite a while after the bolt shears. I suspect it gets up to about 40% speed, lasting about 2 sec before the shear pin breaks.
I'm thinking I need to add a slip clutch to the shaft in order to be able to tighten it adequately to make the system work. And while I've used PTO shafts with the clutch already installed, I've never installed one myself.
Any thoughts on this issue? I know the typical is 'something is too tight and it is binding' but I don't think this is it... I think it just takes 'too much power' to get everything up and moving, and by the time that has occurred, the shear bolt has broken.
PS: I am contacting the manufacturer and telling them about the issue. I think, looking at the situation, that they simply included the wrong size PTO shaft for this machine. A Series 3 shaft would be typically with a 20-25hp machine.
If this is the case, and I want to get another 'domestic' PTO shaft, what is the best source for one? I'd like to get one with a CV joint and a slip clutch if possible. Any options on US source? I need 540rpm collapses to 72" between shafts with expansion of about 12-16" it appears.
