Back in the day when Quadra engines was popular, my cousin bought one. It was a shaker so he sent it to a engine balance person. His name was Dario B. and he did what he called "over balance" on my cousins Quadra 50. It came back & sure enough it was a lot smoother. I seen a very neat engine Dario built from scratch. He is in one of the 4-5 other model engine forums I read once in a while. Capt,n