1970 340 Balance Problem...Bottom Line

With your vibration at 1400 and 2800 u have an engine balance problem, if u were to rev it to 5600 it will be there also, because it doubles with rpm......providing ur neutral balance converter is the problem there would be a continous vibe at all rpms...360s had a weight added till 1978, cast cranks were in 318s for the 1969 model year, BUT were Internally balanced, even up to the end of production....kim........