Conrad's Time Machine (Adventures of Conrad Stargard)

Just out of the Air Force, Tom looked up two of his old pals, one of whom had just wrangled with a Federal grant to study motorcycle gangs. For ease of study, the trio formed their own gang and hit the road, intently studying each other in various seedy bars along their way. Then these poor man's Easy Riders ran into a strange perfectly hemispherical hole in the ground where a house had been, and found the pieces of the machine that had done this. They realised that the device was nothing less than a time machine and they though they could get it working again. Unfortunately, they did, and the world would never be the same...