I've seen two lines of attack on this. The most common is to cut the crank down to fit the smaller block. The other is to line bore the block to fit the crank. Either way requires about 120thousandths to be cut. Sounds like a lot to me. Any advice or information on this? Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Hi Chuck,

I don't know if this helps or not, but I put a 292 crank into a 256 block. I had the block align-bored to match the crank. I did this because of the abundance and price of 292 parts compared to 256, but that doesn't really apply to your situation.

 

 

Ed

Wouldn't the availability of 312 bearings, type/servicability of the main seal, and the condition of the crank be important factors? (If I had a NOS 312 crank, I wouldn't let anyone touch it! A 292 block ruined by an incompetent machinist would be easier to replace). I have heard that a good crank-turning job (especially the seal surface) is NOT something you can take for granted. Line-boring (like ballancing) is often done anyway by those who want the very best motor possible.

6 VOLTS/POS. GRD. NW INDIANA

My personal preference is to grind the 312 main journals on the crankshaft down to the 292 size when given the option and here are some of the reasons I use to justify this.

 

1.      The cost of the 312 main bearing sets are exorbitantly more expensive than the 292 main sets.

 

2.      Bearing speed for the 292 mains is less thereby making the 292 main size more favorable for increased performance and/or efficiency with everything else being equal.

 

3.      The main bolt spacing is an inherit block weakness for the larger main journals.

 

4.      The larger journal mains do not tolerate as much main bolt torque as the smaller sized main bores on the 292’s.

 

5.      The 312 main bearing sets are becoming increasingly more difficult to obtain in the various undersizes and especially in the name brand bearing sets.

 

6.      It’s ultimately less expensive for a machine shop to cut the mains down on a 312 crankshaft versus boring a 292 block out to the 312 main bearing size.  The bearing tang slots must also be put back into the journal bores if boring the main bores out to the larger size.  When boring the mains to the larger size in the block, then a decision must be made early on to either leave the main seal at the 292 size or remachine the block to the larger 312 seal size.

 

7.      Until recently, real main seal selection for the 312 was limited but Best Gasket has solved this issue.

 

Lorena, Texas (South of Waco)

There is one other good reason to cut a 312 crank and that is to use a crank that has had the mains already ground to the min undersize available for 312's.

Doug T

The Highlands, Louisville, Ky.