truck crankshaft

Hello , I plan on using a bbc 427 truck crankshaft in my 396. I was told that I would have to have an area in the rear of the crank be machined out. Something to do with a truck crank going into a car block. Is there a difference between truck and car cranks and the rear saddles area's of the block's? Thanks Ben

 

Your informant is full of it.... Physically they are the same. But, the truck crank is balanced to a much heavier 4 ring HEAVY piston. The crank should be balanced to your ***embly if you value your dentures.. It'll shake rattle and roll at high rpm.

 

The crank will fit with no issues at all. If it was the 427 tall block crank it will be a forged Tuftrided (surface hardened) which is still good to about an .020 journal cut.

You can never get hurt balancing a rotating ***embly but I will say that if it is the truck crank that had the tall compression height 4 ring pistons it indeed will have heavier counterweights which will actually improve the balance if you have lighter piston. That is called overbalance and it was common to have at least a 52% overbalance (more counterweight than needed) with oval track engines as the balance was better at the higher RPM's and improved bearing life in addition to keeping things from spitting out the side of the block.

It is the same thing as putting a 350 crank in a 305...works great. Put a 305 crank in a 350...you have a tooth rattler.

 

For the record. GM's early Tuftriding. (Nitriding) is less than .006 deep in most all cases. Later technology (1990's) and practices have led to more dept penetration.

Also the "overbalance" was only 2% the other 50% is part of the balance reciprocating formula. A true 52% percent overbalance would not stay in the machine...

 

So should I have it balanced for the lighter ***embly or not ? The pistons do have 4 rings. So on the safe side I would ------ the crank. Thanks guys, Ben