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Drivetrain => The Nailhead => Topic started by: moteaux on January 24, 2019, 09:42:44 PM

Title: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: moteaux on January 24, 2019, 09:42:44 PM

I pulled my ST300 and noticed the flywheel alignment hole does not line up with the crankshaft alignment hole.  I believe my 65 GS has a 64 401.  It is a KT109xxxx.

My flywheel has no indications of additional holes or weights for balancing. Does that make sense?
Are there crankshaft differences between 64 and 65 401's?
Are ST300 flywheels interchangeable with other Buick engines and transmissions?
Is it possible to have a non-401 crankshaft in a 64 401?
?And lastly, does anyone have some ideas why my flywheel alignment hole does not align with the crankshaft alignment hole?

I have attached a couple of pictures for reference. Thank you in advance for any help you can provide on this matter.

Title: Re: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: TrunkMonkey on January 24, 2019, 10:36:39 PM

The index hole is a visual aid, so if it is not in perfect alignment, it will be OK.  It is so you do not get it in the "five other incorrect"  positions available.

Pics of the entire flexplate, front and back, will help with the other questions.

Title: Re: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: WkillGS on January 24, 2019, 11:12:25 PM

By any chance is the flex plate installed backwards? I need to take a better look at the pics....
The flex plate has two large open 'window' cutouts, and the third 'window' has a plate in it, so that is your balance. Sometimes there are some partially drilled holes to fine tune the balance.
'64 to '66 cranks are the same, '63- earlier are different for the Dynaflow trans.
Flywheels and flexplates interchange within specific engine families..... 64-66 401 and 425, a 300 flywheel will interchange with 340 and 350.

401 ST300 flex plates have two sets of holes for converter mounting so they can be mated to either the smaller Skylark GS converter or the larger converter used in the big cars. Some other 401-425's have the dual pattern as well, I think 65-66 only?

Title: Re: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: moteaux on January 25, 2019, 07:21:33 PM

I have attached pictures of both sides of the flex plate.  The previous owner marked the sides of the flex plate.  As marked, the raised side of the flex plate was mated to the engine.  Said differently, the raised side of the flex plate points towards the engine.

Title: Re: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: telriv on March 10, 2019, 01:44:24 PM

Looks as if the flexplate was installed correctly
Looks like one of my "Mini" starters


Tom T.

Title: Re: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: moteaux on March 10, 2019, 09:04:59 PM

Tom, that is one of your starters and I couldn't be happier with it. Thank you very much.

Title: Re: 401 Nailhead Crankshaft-Flywheel Alignment
Post by: telriv on March 10, 2019, 09:09:39 PM

I thought so & THANK YOU very much for the compliment.

Tom T.