Farrell, No chance, Bought an engine fully rebuilt but had sat for couple of years, installed it, ran it down the road , sounded like crank was going to fall out, HARSH , not vibrating, pulled down, crank bent 4 thou, straightened it, same noise , pulled , balanced , same noise, pulled sent to a good rebuilder, new couter balanced crank fitted, cam bearings, new white metal on rods, insert mains ok , rings, valves, balaced , etc, fitted back, same dam noise, pulled rebalanced , same noise, It sounds like crank wants to fall out, above 30mph , below fine, Either mains off centre line or bore line has been moved, you can,t push piston straight up & down it needs to oscillate, like figure 8 pattern, Im leaning to an off set guegon to fix it, Might try Daves suggestion on custom pistons once checked, All other engines have built myself, one is happy at 5800 revs & smooth, so i know something is not inline ,
Good news is i fitted steering rods by above ideas, so all not lost, One is never too old to learn, Heading to Boise meet in 2 weeks, Team leader for modified,