I have been rebuilding Austin Healey 3000 BJ8 engines for three years. We have done many successful rebuilds. The last 8 engines all appear to have a bearing issue. We are seeing scratches on the main bearings. A typical response would be that there is grit in the motor. In an effort to determine the source of this problem we have painstakingly gone through every cleaning procedure and examined every component of the engine before assembly. All of the machinists have 25-35 years of experience. I am confident in the machine work that is being done. We have checked and re-checked everything before and during assembly. I am at a total loss and need information. We are spinning the engine on an electric test stand and after an hour we see scratches on the bearings. We have been using the Brad Penn 30 wt. break in oil. We use a Fram oil filter. Any ideas of what we could be missing or not aware of? We rebuild many engines and have no issues with any engines other than the Austin Healey. Thank you!

Perform a Used Oil Analysis (UOA). It may highlight sand (from casting) or some other culprit. Send an oil sample to Blackstone Labs. Are you using assembly lube?