1966/67 Flywheels vs 1968 and later

[Norton1]

I have been told there is a difference in the 400 ci motors. But I can not figure out what it is. Anyone here know? It's for a manual tranny -

Thanks,

Steve

[joe_padavano]

Steve,

Same answer as on 442.com. As far as the flywheel is concerned, the crank flange bolt pattern is different. As for other differences, the 65-67 400 uses a 4.00" bore and a 3.98" stroke on a forged crank. The 68-69 400 uses a 3.89" bore and a 4.125" stroke on a cast crank.

The reason for the two very different motors with the same displacement starts with GM's corporate limit of 400 cu in on the A-body cars. Olds wanted to save cost by reusing the expensive crank forging from the 425. The existing 3.98" stroke dictated the bore. Yes, the early 400 and 425 cranks are the same. In 68, Olds increased the stroke of the 425 to make the 455. Again, Olds reused the (now longer stroke) crank on the 400, which required the smaller bore to stay under the 400 cu in limit.

[Norton1]

Joe,

Thanks. I'm off to an old wrecking yard today to sort through hundreds of old flywheels in search of a flywheel for my 66. I had toyed with the idea of using a later flywheel and simply remachining the bolt holes to fit my 400. They are not off by very much I've found. But I am unsure of how they balanced the flywheels. The cranks, at least in my experience, area all balanced at the factory. So if I reset the holes and static balanced the wheel it should work fine.

I think I'd also use a fluid filled harmonic balancer on the motor to ensure a vibration free motor.

If I do find one of each I may go ahead and try the idea out. If it works it would be the salvation of many of us with the older rigs. Not to mention the savings over Joe Mondello's $400 flywheels. Not that his aren't worth it - just really spendy when you are on a fixed income and working like we did in the 60s and 70s on these automobiles.

Thanks again.

BTW - Mondello's tech line will FAX anyone a copy of the bolt flange differences with schematic included.

Steve

[joe_padavano]

There's one on ebay right now...

[Norton1]

Yes - I saw that. $150 is his minimum. So I went to the local wrecking yard. The old boy who has ran if for the last 50 years is tired of it and has turned it over to the local hot rodders to clean up some of it. I went through a van full of flywheels and found one. $20.00. Made my day.