What's the max you can turn down a 455 crank and still use Olds rods? I'd seen bearings for .040 undersize so can I assume that's the max?

 

It's a function of the bearings you can get. I'm guessing that 0.040 is probably the max, since as the bearing shell gets thicker, it can move around more and run the risk of spinning. The crank journal itself really isn't the limiter, as people turn them down all the time to use Chevy rods with a smaller big end.

 

Gotcha. Thanks Joe.

 

I *THINK* i read on a site that they could add material via welding to the crank and turn it back down. did I understand that corectly and if possible is that a good idea ?

 

Hmmm not sure I agree with you there Joe, at least I'm not sure exactly what it is you mean.

As per a Clevite engineer;

Std and .010 under bearings use the same thickness on the outer shell.
Then .020 and .030 under share the same shell as well. Only a .040 will have a bit more tin and copper in each half than either the .010 or .030 under bearing. So I'm not sure how a thicker overall bearing shell will move around more. Remember the bearing thickness will increase on the i.d. so the bearing tang will still hold them in place no matter what the overall thickness of the shell, not to mention they will still have the same bearing crush all else being equal.

 

Mark,

Yeah... maybe that wasn't the right term. I'm ***-U-MING that there's some upper limit on the overall thickness of the bearing shell. At some point (consider a half inch thick shell for the sake of argument), the added lever arm of the bearing thickness could lead to the shell walking around in the rod, probably fore-aft, actually. I don't have any data on this, but I've got to believe that there is some practical limit on this.

 

Hmmm... not really. King Bearing has been making rod bearings that allow you to run larger journal SBC rods on a small journal SBC crank. They work just fine, even in mild race applications.

 

OK, cool. I stand corrected.

 

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Short answer: It depends.
Here is a link: http://crankshaftrepair.org/welding/#more-134

Author suggests there are limits to how far it is practical to grind a crankshaft before welding it back up to specs is a better solution.
Caveat: they are in the crankshaft welding business.
Jerry