Two different crankshafts

[ppower]

I am rebuilding my Ford model A engine using an engine block from an engine I bought as spare.

The two engines have different crankshafts which seem to be interchangeable. The main difference is the shape of the diagonal webs although the crankshaft with the stouter diagonal webs has circular webs of slightly less thickness.

Can anyone explain the history of the changes?

 

[Rowdy]

Steve Plucker has the info on his website. I believe the change was in mid 28. Yes, they interchange without a problem as the throws and all critical dimensions are the same. Rod

 

[Kurt in NJ]

The thin one is forged , the thicker is cast

 

[John Stone]

The thin one is forged , the thicker is cast

I believe both are forged.

 

[wrndln]

I agree with John, model A crankshafts are forged.
Rusty Nelson

 

[BILL WILLIAMSON]

Should I pop mine out & inspect it?
Bill W.

 

[Tom Wesenberg]

I wouldn't go racing without a counterweighted crankshaft.
In fact I won't even assemble my slow driving engine until I get the counterweights on the crankshaft.

 

[Chuck Sea/Tac]

The thin one one is 28. I hear they flex more. I've been told early racers liked them because of less weight and oil drag?. I have a standard one myself.

 

[ppower]

Many thanks, Presumably the reason for the change has been lost in the mists of time.

 

[Kevin in NJ]

Hard to be sure from the pictures, but it appears to me that the upper crank does not have a proper radius at the corners of the journals.

If that is true then you have to be worried about cracks and it certainly should not be used as is.

 

[johnneilson]

The thin one one is 28. I hear they flex more. I've been told early racers liked them because of less weight and oil drag?. I have a standard one myself.

Yes less MOI to accelerate.
However, what they didn't tell you was that the cranks were changed after just a couple races. The fact of the matter is just how good the machining was for that time.

J