I built up a Miyata from the bare frame. Everything worked fine for 50-75 miles. At that point the Sugino Super Maxy crankset began to slip. I removed the crankset and inspected it for damage and seeing none I reassembled and immediately it slipped again when pedaling. I used a Sunlite SL-26 cartridge BB size 68 by 118mm with 1.37” by 24T English thread. Drive train aligns perfectly.

No metal grinding or damage, just slips. Weird because it worked initially. Any thoughts? Thanks.

What do you mean by slip? Is the chain skating on top of the chainrings? Is the rear freewheel used or new? New chain? Sometimes worn freewheels and chainrings with new chains will slip like you mentioned. it could also be how you are shifting. The freewheel pawls may not be engaging properly. Lots of possibilities.

The freewheel and chain are new. The chain fully engages with the FW and CW. However, the hub is old. Maybe the hub is stripped, causing the FW to slip. I will try the bike with another set of wheels. Thanks for your message.