I'm in the process of building a 292 with a steel crank and my machinist has a concern about the radius area where the journal meets the throw. Radius is a little tight or should I say a sharp angle. For a performance build should the crank (which is a useable standard) be ground .010" and have more radius built in?  Better oiling? Would a better route be a nice polish and go with a .001" bearing? All opinions welcome. Thanks.

Unless you widen the journals or do a very significant undercut, the existing radius is what you’ll have to live with.  Building the journals back up in this area and then remachining for a larger radius is typically not recommended as this leaves a stress riser in the radius area and potentially makes the crankshaft weaker than what you started with.  Turning the crankshaft 0.010” undersize will not be enough of an undercut to allow any significant increase in journal radius but with due diligence, the existing radius can be maintained.  The other consideration when making a significant increase in journal radius is the clearance to the bearing and possibly the need to narrow the bearing itself so the bearing is not riding against the edge of the radius.

 

A good balance job will overcome some of the crankshaft shortcomings in relieving certain stresses imposed on the crankshaft.

 

Absolutely nothing wrong with using 0.001” oversize bearings if you can maintain your desired bearing clearances.

 

Just one opinion.  Any others welcome.

Lorena, Texas (South of Waco)

I have never been pleased with .0010 bearings. If it polishes up standard I use standard. If not I do what I have to do. Back in the 60's I had a .20 under steel crank that outlived the rest of the engine several times. I am in the process of building a 292 out of a NOS service block I recently found. I have a .030 under steel crank that I bought 40 years ago for a spare and I'm going to put it in the engine I'm building. I can live with a little too much clearance, but when bearings get tight, bad things happen. And I've seen that happen with .0010 bearings.

Kenneth

Fredricksburg, Texas