Ok so the 1966 401 is an externally balanced motor. If you have a motor that came out of an automatic car and you want to put a 4 speed trans on it instead of the automatic what balance changes need to be made ? Obviously you need the pilot bushing for the trans in the end of the crankshaft but how do you make sure you have the balancing part correct ? Did Buick use 2 different crankshafts 1 for standard and 1 for automatic ? Service/Chassis manual says your supposed to line up the guide hole on the flywheel and the hole in the crankshaft for correct orientation. Is the flywheel thicker/heavier on the 4 speed motor to compensate for the weight of not having a torque converter ? Did the 401 use two different harmonic balancers so you have change it from an auto to a 4 speed car ? Probably over thinking this but would like some wisdom on this.
Hi, Just get a flywheel for a 401/425 and you should be fine, as my car has a 64 401 that had a 400 trans attached before I converted it to a manual transmission, put a stock GM cast iron flywheel on it and later a TA billet in 2012 both no issues, car has been together since 09 and no issues with vibration, car goes 80mph at 4000 rpms with no issues than lots of exhaust sound, lol Depending upon the route your going manual transmission parts for a A-body are relatively rare, as all unique to 65/66 Gran Sports, aftermarket might be more options if you go to a hydraulic clutch. Good luck with the project Regards, Jim
Thanks Jim I thought I was overthinking. I have a factory set up for a 66 GS flywheel bellhousing Z bar etc. etc. Just doing to much reading in this Chassis Manual. Best Michael
Just remember that the flywheel/flexplate will mount in six different positions, and five of them are wrong.
