Small Engines (Lawn Mowers, etc.): snowblowers, shear bolts, head gasket

Question
I have a Sears 8 horse, 28" cut that will not throw snow.
Belts have been changed, impeller bearing and head gasket has been changed, it will only throw snow 2 feet. Machine is approx. 20 years old. any suggestions what else to check?

Answer
Are the main auger shear bolts sheared/broke?  If you have a two stage model, is the second stage impeller key wore or broke?  Did the unit work fine last snow season?

I would suspect something is wrong with the impeller.  Did the shop who replaced the impeller bearing install the aguer tines correctly?  Some models have a right and left side.  Install the tines backwards and the machine will throw snow out the front of the snow bucket rather than pulling it in for the second stage to blow it out the chute.  I have seen this problem several times where the customer installs the aguers backwards.

Let me know.
Eric