Hi all,

I was wondering if I can put a 67 forged crank into my 78 block? I figure I have to have the cast balanced anyways cause I'm replacing the pistons. A local guy here in town has one so I can go and measure it up to see how the mains and journals are. Will they be 2.75" mains and 2.375".

One other thing, I know I'll have to replace my balancer, but what about flex plate and torque converter? Thanks all.

Joe Welder

 

"Balance" implies the entire rotating mass. Even on an "old school" "balanced" 440, if you went in there and replaced the rods and or pistons with something different, the thing is no longer balanced.

One example is the 440sixpacks. My 70 was an externally balanced engine, because Ma had gone to heavier rods. Don't know if they changed the pistons from 69 1/2 to 70 or not. So basically the real change was the rods.

So the point is, if you build an engine, and use pistons, rods, different from the weights of the originals, "it ain't balanced no mo."

But if you are CLOSE and use a crank (forged) from an internally balanced engine, then GET THE MASS BALANCED and YES you will need an "internal" balanced balancer and flywheel or converter

 

My terminology is forged and cast and internally or externally balanced. Swaping a crank from one engine to another requires another step.

Because it's from another engine the mains will have to be align bored for the crank that it not virgin to that block.

I take my crank, rods, pistons and piston rings to the machine shop and all of the pistons and rods are made to weigh the same. The bob weight is calculated and then the crank is balanced. Then they spin it up on a machine to check the balance. I get charged 250 bucks for this. Turning the crank first costs me 55 to 70 bucks at the crank grinder.

 

Thank you for the response, based on that info I will pass on the forged and stick with my cast "externally" balanced crank. Although technically I guess it's not balanced anymore seeing as I don't plan on reusing the pistons.

The machine shop prices up here are substantially more than where you are, as an example, polish of the crank here is $68, I'd be afraid to ask what an align bore costs. Haha. A balance is $450. Thanks again. Great help. I'll figure this all out eventually.

Joe Welder

 

You would need to re balance the motor, Personally I don't think you need to align hone the block unless the old bearings show strange wear patterns for a semi stock rebuild <500 hp or doing a complete blueprint. The motor can tell you a lot when you take it apart and measure everything. When you have the crank re ground it is no longer a virgin either... I would go with the steel crank. As I broke a cast crank in a 360 once...

 

Placing a strange crankshaft in an engine that it was never in will need to be align honed.... the mains will have to. They did that at the factory to make the crank fit the mains. I tried putting a forged crank in another engine block and it didn't want to go. I was referring to him wanting the forged crank out of the 67 block into his 78 block. Even if you buy a new crank you will have to align hone the mains of the block it is going into.

 

Just from speaking to the gentleman with the crank for sale, I have a feeling that it is in great shape. He is a mechanic who wants to do a stroker and once he found out the difference in buying a kit (that can be ordered balanced) compared to having to source individual components and still have to get the balance afterwards he decided that he would go the kit route. He is only asking $250 O.B.O. So I'm thinking what I could do is throw my block on a pallet (with my bearings) in the back of the truck and drive it down there with my dial cal and an outside mic and check it out.

Should this crank measure up the same as my cast? i.e. overall length etc. I'm just thinking from a timeline standpoint. 67'-78' 11 years? Thanks guys. This is one component I want to get right since it will be the foundation for the whole project.

Joe

 

I am now the owner of a forged crank! The mains and journals are within a couple of thou of tolerance, and the runout is less than a thou with my old bearings on the 1&5 mains. I may need a grind but I'll bring it to my machinist friend to determine that for me. Wasn't a bad price either $200, considering how much more we usually pay here in Canada. If i need a grind it's $185. So for less than $400 i'm into the steel that horses are made out of.

Cheers,

JB

 

I once put a forged crank from a 71-440 into a 75 block that had came with a cast crank. The motor ran great! Of course I used the forged crank balancer, and had the assembly re balanced as I was using K B pistons.