289 crank pilot size for automatic


New Member
Sep 14, 2018
Farmington MI
I have a 65 A code Mustang with the stock C4 automatic, case fill, small bell, 157 tooth, 10.5" torque converter(TC) bolt pattern, 28.2 OZ offset weighted flexplate. The engine is a real 65 289 HP long block with cast iron headers, complete. I have had drive train vibrations problems for years with this setup. It has destroyed one TC and trans pump allready. The plan this time is a new TC, and flex plate again. Pull the bell off the trans and check dowel pin alignment. The question is, as nearly all 289 HP engines were in 4 speed cars, the small 4 speed crank bushing has been removed, is there a size the crank needs to be for the TC pilot? or is the TC bolt-centric? TC's for this trans are threaded stud type with nuts. I guess I could ask the TC people, but I value you opinion :)
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A true HiPo 289 requires a special 30.4 Oz flex plate or flywheel.
They also had 2 weights up front, a 24.5 Oz balancer and a 5.9 Oz counterweight which equals 30.4 Oz.
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That’s interesting info, and could explain things. Yes I have the internal offset weight, as well as the thick dampener, it Is a real deal 65 HP and on the registry as engine only survivor from the hand stamped vin #. So even if it was a 4 speed version, it would have 30.4 offset weighted flywheel, I have not hard of this, but I will say going through the engine everything was different than a standard 289
It uses heavier 3/8" rod bolts vice 5/16".
There were 2 flex plates made for the HiPo.
Part Number C4OZ-6375-C (which may have a dab of orange paint on it) and C4OZ-6375-E (which has a C7ZP-A stamping on it).
You sir are correct, Found a 2008 Fairlaner article by Bob Mannel indicating a 30.4 offset weighting for the 289HP for flex plate or flywheel, and flexplate
C4OE-6375-C or none or painted marking such as special or HP C7ZP-A Thank you again. So I just have to glue on a couple nickles on a 28.2 oz flex plate and...