Further to ... a few years back I had problems with this same blower and it was determined that the chain was incorrectly installed during the original assembly. The unit had to be taken apart and reassembled by the dealer. Not sure if this may have corrupted the unit internally but clearly something must be wrong with the mechanics if I cannot operate at high throttle speeds without continually breaking the impeller pins.
At this point I may investigate reaming out the impeller pin holes and installing a stronger bolt. I can't imagine this would damage the gearbox if I am only pushing light snow.
Cheers everyone !
A couple of thoughts...
1) I would suggest you do a "divide and conquer" method of troubleshooting. Pull the impeller sheer bolt out entirely. Pull the short driveshaft from the blower to the quick hitch entirely. This will leave you with just the impeller and chain reduction drive to spin independently of the augers and gear box.
Spin the impeller by hand. See if it's catching on anything, indicative of a bent impeller shaft. Feel the running tension on the drive chain. When I've done this I can feel the "click click click" of each chain link running across the teeth of the sprockets. Feel also for backlash or slack in the chain. There should be some. Given the size of the chain links themselves and the small distance between the sprocket centers there's very little option available to get the chain to fit perfectly - some slack will be present in the chain. There should not be enough slack to allow a chain link to have to rise up to climb onto the sprocket.
Spin the augers by hand and feel how they and the gearbox run - should be quite smooth. You'll feel some backlash between the two augers; that seems to be perfectly natural as I've felt it on all three of my blowers as well as on brand new ones at the Kubota dealers. If the gearbox is bound up then you should be looking there for the cause there. I highly doubt it would be so bound up as to break a shear bolt.
2) rather than trust the dealer, go to a fastener supplier and source the correct Grade 5 bolts to use as shear bolts. While the Kubota dealer is not likely providing the wrong part, we do know that shear bolts for the impeller should be grade 5, and we don't know for certain the grade of the part being provided by the dealer. Again, I don't intend to impugn your dealer but rather I am suggesting they are working with what they get from Kubota which may not always be the right part.
As I've been writing this I've come up with one other thought... There is a potential for you to have a bad input bearing on the impeller shaft. This would allow the rotational forces to escalate quite dramatically when under load. Again, with the shear bolt and input driveshaft removed, play around with the impeller to see if that input bearing has play in it.
And yet another thought... The chain sprockets are held onto their respective shafts with Woodruff keys and grub screws. Make sure those grub screws are tightened down and that you've actually got the Woodruff keys in place.
EDIT: It took me far too long to write the post above Clearly the OP has found the cause of the problem. The right part is critical to success!
