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#1
12-29-2011, 02:43 AM
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61 Pontiac 389 Crankshaft Change
Dear Members,
I'm in the process of rebuilding my 61 Bonnevilles 389. During the rebuild I want to change the rotating asymbly to make it a 421. The car has a Hydramatic transmission and I am having a problem locating a forged aftermarket crankshaft with the bolt circle and size that will accept the Taurus coupler ring /gearless flexplate. I want to keep the Hydramatic transmission so the adapter plate to use a later automatic is a direction I don't want to take. I would appreciate you help. Sincerely Gmil60 |
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#2
12-29-2011, 11:03 AM
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Why do you need a forged crankshaft for a cubic inch upgrade? A stock cast crank will work fine except for a race-only engine.
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#3
12-29-2011, 01:17 PM
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389 crankshaft change
You are right for my street application I don't need a steel crank. I decided to upgrade the lower end when I had it apart. I received a build proposal from Butller which gave me the idea to change out the lower end and upgrade the cylinder heads. If I can't find a aftermarket crank to work I will probably use a cast 421 crank. I spoke with Buttler performance, I'm in the process of sending my flex plate to their shop so they can match up a crankshaft and check the spacing.
Sincerely Gmil60 |
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#4
12-30-2011, 04:18 AM
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Quote:
I'm guessing you were trying to say "torus cover" (see 'torus' in any dictionary); but your [mis]spelling gave me quite a chuckle!
__________________
Anybody else on this planet campaign a M/T hemi Pontiac for eleven seasons? ... or has built a record breaking DOHC hemi four cylinder Pontiac? ... or has driven a couple laps of Nuerburgring with Tri-Power Pontiac power?(back in 1967) ... or has a Pontiac born the same year as Jim Wangers? (1926} 
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#5
12-30-2011, 08:01 AM
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Being this is my first Pontiac, I did not realize the bolt circle on the rear crankshaft flange was the same. The majority of the rotating parts I am ordering through Butler due to their experience with Pontiac Engines. The actual question arose when I got ready to order the forged aftermarket crankshaft. I was asked by Butler to check the bolt circle and spacing of the flex plat and it did not match anything they had in inventory to send me. I can only assume companies like Scat seem to be making crankshafts mostly for late Pontiac engines.
Oh!! by the way I'm glad I gave you a chuckle with my spelling of Torus. I never knew anything like a fluid or hydraulic couplers existed before the purchase of this car. Thanks for your input Regards gmil60 |
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#6
12-30-2011, 11:10 AM
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[QUOTE=pontiac jack;4506674]Every single Pontiac V8 '55 - '81 used the same crank flange bolt pattern.
QUOTE] Jack are you sure on this? I thought there was a change in the late 50's |
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#7
12-31-2011, 01:33 AM
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The crank flange bolt pattern did not change in the late 50's. What did change was counterbalancing material was added to the flange which prevented bolting up a 55/56 dual range without removing a little material on either the flange or the flywheel. It is only a problem with the dual range. That was discussed here some time ago and is discussed at this link.
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