Shipwright, If you have a rebuilt pressure plate and most are these are netorious for being out of balance. This information came from my mechinest who has ben messing with these engines for 45 years. Remove it and the fly wheel and take it and have it balenced. I had the same problem in my 53 235 and it fixed the problem. Make sure that they make a witness mark so you can align everything when installing the pressure palte to the fly wheel. Hope this helps
