You say "impeller". Do you mean the fan? The other shear bolts pictured above are for the augers, which I have blown several times with no damage. I use the proper Kubota shear bolts.
Now if it is the "fan" part, there are 2 different designs of the BX2750D. Earlier models used a grade 8 bolt through the shaft (and fan sleeve), one that was also grooved to provide the proper shear points. Newer models have a smaller 1-1/4" grade 5 bolt through a flange (double flange) between the fan and the flange mounted on the shaft. I find that is much more reliable and easy to replace compared to the older grade 8 bolt system. The old grade 8 bolt was a bear to get out at times.
I had the older 2750D model and found that after a few blown fan shear bolts, it became harder to align the holes to replace the grade 8 bolt. I suspect things got twisted or bent over time, probably because of too much stress. It got so frustrating that I bought the newer model with the simple grade 5 bolt on the fan portion. I keep the old blower for spares (except the drive shaft and fan)
As for the chain, remember to lubricate it, every 4 hours I believe, with chain saw bar oil. I pour a bit in the open hole every time I take the blower out to clear snow.