A single stock key on a BBC will work to about 9 Lbs. with a 6 or 8-71, no problems. To do your deal, just replace the stock crank key with an alloy/ hardened one. Pioneer sells them as a PK-9 for the stock and a PK-9A for the alloy key. Then it will work fine to 16-17 lbs. boost. The guys that are shearing them off usually have strip-sealed 6 or 8-71s or have backfire problems on startup, and that will wallow out the keyway just a bit everytime that it happens until the key finally shears. If the key shears cleanly then it was just a stock key- too much boost issue. We are a dealer for most blower companies, and have a full machine shop here too. Make an appointment, and go have lunch or take the Missus shopping and your crank will be keyed any way you want it by the time you get back here! We are in Avondale,AZ. just off of I-10, easy to find! TIMM