are fully grooved and oil the connecting-rod journals 100 percent of the time. Upon grinding journals to final dimensions, it is not necessary to nitride treat nodular-iron crankshaft journals. Nodular cranks are very durable, and hold up just fine through the 600-hp level, as do the forged-steel cranks. Beyond these power levels, it’s a coin toss as to which will fail first, the block or the crank. I am not saying nodular crankshafts absolutely fail at horsepower levels beyond 600; I have seen them live at higher outputs. I just have never seen a crankshaft break at the 600-hp level, and consider it a safe target for those choosing to use a factory nodular crankshaft.
As of this writing, the only aftermarket production Oldsmobile crank-shaft produced is the big-block crank made by Eagle. It is characterized by Eagle as being a “cast-steel” crank. I have used some of these cast-steel crankshafts in some Pontiac engine builds making about 800 hp (with nitrous oxide) and they’ve never failed. I have found that the grinding job on these units is not necessarily flat, round, or sized properly, and required rework to be perfect. When purchasing these units, you should inspect them closely, and expect to grind them to suit your particular application.
Bryant Racing and Velasco Crankshafts make top-of-the-line billet crankshafts for Oldsmobiles. This 4.600-stroke model is made with premium material, center counterweights, hollow main journals, and many other features. The stiffness of the crankshaft reduces cap walk and main-bearing issues especially on the number-2 and -4 main bearings.
Crower has also manufactured a few Oldsmobile crankshafts. This model has big-block Chevrolet rod journals and a 4.250 stroke.
On most of my 750-hp or more powerful builds, I use Billet Bryant crankshafts that have a 4.600-inch stroke. You can make one with more stroke and get it to fit, but the 4.600 version fits well in the block without too much headache.
Custom-crafted Oldsmobile crankshafts are available from Bryant Racing, Velasco, and Moldex, all of which are experienced in manufacturing premium-quality competition crankshafts for all big- and small-block applications. These crankshafts are expensive; manufacturing lead times range from 8 to 16 weeks, depending on the manufacturer’s plant loading. For those who need them, they are worth the wait, and they represent the absolute peak of quality.
The price of these premium aftermarket crankshafts goes up as you add features. Expect to pay between $2,500 and $3,500 for a billet Oldsmobile crankshaft as of this writing. These more expensive billet crankshafts incorporate lightened, scalloped, and knife-edged counterweights. They feature hollow main journals, a center counterweight, drilled and lightened crankpins, a scalloped rear flange, and a surface-hardening treatment (such as nitriding).
The biggest advantages of using these billet units are less rotating weight and less crank flex. These two points are reasons why your high-performance Oldsmobile engine may live longer once equipped with one.
If your goal is to rebuild a stock street cruiser that will never see more than 3,000 rpm and will use a stock stall converter, there is no reason to read beyond this paragraph. Factory clearances and standard crank-grinding procedures are fine for your application.
However, maximum-performance engines require additional bearing clearance. You cannot check clearances at the time of assembly. By then it’s too late. Proper clearances must be designed into the build and be part of the plan from the start.
You can’t just take your crankshaft to a crank grinder and tell him to grind your crank 10/10 (.010 inch removed from the main-bearing journals and .010 inch removed from the rod journals). You will get your crankshaft back with standard crank journal diameters and should result in factory clearances with a standard bearing. Performance Olds engines require additional clearance. Your typical high-performance Oldsmobile engine cannot live with standard factory clearances.
As we know, all gasoline production Oldsmobile blocks are weak. Factory crankshafts, both iron and steel, flex when used in performance situations. As more torque is produced, both are stressed and the crank starts to bend and flex like a piece of linguini while the block is also flexing and moving. Therefore, allow enough bearing clearance so the flexing doesn’t result in the engine clearancing itself because of the crank journal contacting the bearing. The higher the RPM, and the greater the weight of the reciprocating components, the more the connecting rods stretch and the sides of the bore close in. This requires more bearing clearance to compensate. If you stick to the factory .002-inch-clearance stuff, there is a good chance of trouble.
When measuring bearing clearance, always measure vertical clearance. The horizontal clearance is always larger, depending on how much eccentricity is designed into the bearing.
The back-and-forth thrust clearance measurement, without the center main cap installed, should read the same as when the center main is torqued in place. If it is not the same, the cap is not in the proper location or the mating surface of the main cap is not square to the thrust surface.
The only way to measure exact bearing clearance is to use micrometers and dial-bore gauges. Don’t stress out over a few tenths here or there. If you have enough clearance, those few tenths won’t mean anything.
If the clearances are too tight, and the bearing touches the crankshaft journal, the spinning engine parts grind against each other and machine themselves. If your bearing clearance is a little loose, there is no negative. I will not build a high-performance Oldsmobile engine with less than .0035 inch of bearing clearance on the rod journals and .0040 inch on the main journals. The more power the engine produces, the more the components flex, and the more clearance is required. My personal 1,200-hp, 8,800-rpm, nitrous-enhanced Oldsmobile small-block engine has .0049-inch vertical clearance on its 2.500-inch main journals and .0043-inch clearance on its 1.888-inch (factory Honda-size) rod journals.
To make sure you didn’t install the incorrect undersize bearing, or if you simply do not have access to micrometers and dial bore gauges, use a feeler gauge to measure the vertical clearance. This has to be done with the bearings dry; oil takes up some clearance. Forget Plastigage.
Experience has taught me that when a main bearing is tightened to specification (torqued) in the block, or a rod-bearing cap is torqued on a connecting rod, the bearing bore diameter will be pretty close to .0020 to .0025 inch over the nominal spec. For example, torque a big-block Oldsmobile rod bearing in a connecting rod, and it measures 2.5020 to 2.5025 inches
