Читать книгу Oldsmobile V-8 Engines - Bill Trovato - Страница 9
ОглавлениеCRANKSHAFTS
The crankshaft transfers all the power made in the combustion chamber to the transmission. In high-performance applications, it needs to be incredibly strong. This chapter will be your guide to the best-possible crankshaft choices for your particular engine build.
Factory Small-Block Crank Identification and Application
All 330-ci Olds engines (1964–1967 model years) were produced with a forged-steel crank. The 350-ci Olds engines produced from 1968 to 1972 were fitted with a nodular-iron crankshaft. Those 350s made from 1973 through 1975 could be either nodular or gray iron, and then gray iron material in all of the 1976 and later engines. All of the small-block 350 Oldsmobile cranks had a 3.385-inch stroke with 2.125-inch-diameter rod journals and 2.500-inch main journals, with the exception of the 350 diesel engines. These had a 3-inch main-journal diameter and were made of nodular iron.
The 330-ci crankshafts are easily recognized by their smooth surfaces, rounded counterweight noses, and wide parting lines on the forging. Use of this crankshaft requires a 330/400/425 flexplate/flywheel because the 1964–1967 small-block flange bolt pattern is different than the 1968-and-later Oldsmobile bolt pattern. Cast-iron 350-ci cranks are easily recognized by their somewhat rougher surface, squared-off edges on the counterweights, and narrow parting lines. The nodular-iron crankshafts are readily identified by a large “N” or “NA” designation cast into the number-1 counterweight.
These three versions are all dimensionally and functionally interchangeable. Although the steel crank is desirable for roughly 600- to 800-hp small-block engines, the nodular-iron crankshafts are very durable in the range of build that the gas 350 block will tolerate. The 350 Olds main bearing webs in the block will likely fail before your 350 nodular crank. The nodular-iron cranks support about 600 peak horsepower. The gray-iron cranks are well suited for stock and moderate performance builds up to about the 400-hp level.
Factory Big-Block Crank Identification and Application
The 1964–1967 “short-stroke” 400-ci engines were produced with forged-steel cranks and are the same as their 425-ci brothers. Later-model (1968–1969) “long-stroke” 400-ci engines could have either cast nodular-iron or forged-steel crankshafts. Most of the big 455 Olds engines produced from 1968 to 1972 were equipped with a nodular-iron crankshaft, but a forged-steel unit can be found. There is wide speculation on exactly where these forged crankshafts were used, but ultimately, there seems to be no specific application where you can be sure to find one, and they’re very difficult to find.
The thin parting lines on the ends of the throws indicate 350 nodular-iron crankshafts.
Notice the undercuts in the ends of the rod and main journals on this 350 N crankshaft. At a quick glance, even with no micrometer, you can tell if the shafts have been ground undersize.
The 330 Olds crankshafts were all steel with the 3.385 stroke. They always have the wide parting lines at the ends of the rod journals and have a smooth finish compared to cast-iron crankshafts.
This part number, 388776, identifies a 330 Olds steel crankshaft.
The older 400 short-stroke and all 425 Olds cranks were steel and appeared very smooth (shown). You can verify that it is a 400/425 versus a steel 455 crank by the lack of a lightening hole in the side of the rod journal.
As with small-block cranks, steel big-block cranks have a smooth look, a wide parting line, and rounded crank-throw noses. The cast 455 cranks have narrow parting lines and squared crank-throw noses. The 455 steel crankshaft is extremely heavy. The weight possibly negates any material advantage there may be over a nodular-iron unit in applications less than 600 hp.
The 400/425 needs the counterweights cut down about .300 inch (shown) to fit in a DX block. You only want to cut as much as you need to fit in the block to avoid having to add expensive Mallory metal.
Depending on the bobweight of the rotating assembly, you need to install Mallory slugs in the counterweights. Expect to pay about $25 to $30 per slug plus the cost of installation. A balance job can be pretty pricey.
The 1973–1974 455 crankshafts could be either nodular iron or gray iron, and they were made exclusively of gray iron material until the end of the original 455 production run in 1977. As with the small-block crankshafts, the nodular-iron 455 cranks are identified by a large “N,” “NA,” or a small “CN” cast into the number-1 counterweight. You may notice that “CN” crankshafts have four lightening holes in the rod journals rather than two holes in the front and rear rod throw as on “N” cranks. Most of these are also machined for pilot bushing installation. The more of these I see, the more I think that they are the nicest of the Oldsmobile 455 cast crankshafts.
This “CN” crankshaft is easily identifiable by the four lightening holes in the rod journals. They are the lightest, best-cast Oldsmobile crankshafts of all.
The nodular cast crankshafts for 455s have a rather large “N” cast into the counterweight. In addition, they can have a small “CN” cast into the counterweights on later models. If you cannot find either, you have a low-performance, late-model crankshaft.
Unlike the small-block family, 425 and 455 cranks do not directly interchange. The 425-ci version has a 3.975-inch stroke with 2.50-inch-diameter rod journals, 3-inch-diameter main-bearing journals, and a flywheel/flexplate bolt pattern that matches the old 330 crankshafts. The 455 has a 4.250-inch stroke with 2.50-inch rod-journal diameter and 3-inch mains, and is drilled for the later flywheel bolt pattern that matches all the later small-block flanges.
The 455 forged-steel crankshaft is the heaviest crankshaft; these weigh about 90 pounds.
The 455 forged-steel crankshaft is very rare and often described as rather ugly.
This 425 crankshaft was knife-edged on the CNC machine. Forget doing this operation by hand unless you have nothing but time.
The wide parting line on the rod journal and lack of a lightening hole easily identifies a 400/425 crankshaft.
The easy way to identify a 455 forged-steel crankshaft is by the lightening hole in the rod journal.
Both the steel and nodular-iron crankshafts typically support more horsepower than the 455 blocks handle in ungirdled applications.
The biggest single performance improvement that can be made to the factory Oldsmobile crankshaft is to have the crank properly and professionally ground. This is the only machining investment necessary on a factory cast-iron crankshaft.
It is not necessary to cross-drill factory Oldsmobile crankshafts for increased oil flow; the main bearings 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 for a standard-size bearing. Similarly, torque a big-block main bearing in a big-block housing bore and the inside diameter measures 3.0020 to 3.0025 inches on a standard-size bearing. The actual bearing clearance is the inside diameter dimension of the bearing in its housing, minus the dimension of the journal’s outside diameter (OD). In general, the inside diameter of the bearing in the connecting rod and main journal is .002 inch over the nominal dimension. On undersized bearings (meaning .010-inch, or .020-inch, etc.) you simply subtract the undersize you are using from the nominal dimension.
As-manufactured or machining size errors can and do happen. Machinists sometimes make errors when sizing journals or cylinder bores, and there is a plus-or-minus size tolerance to the actual thickness of the manufactured bearing shells. Occasionally, mistakes are made in packaging or labeling manufactured parts. It never hurts to torque up a bearing in a rod or main journal and measure it yourself. The best way to achieve what you want is to torque up your bearings, measure with a dial-bore gauge, subtract the amount of clearance desired, and give that dimension to the crank grinder.
What should your bearing clearance be? See sidebar “Bearing Clearances” for my recommended bearing clearances. Keep in mind that non-rigid components require more main bearing clearance than more-rigid components. For example, an engine with a relatively heavy piston teamed with relatively soft factory connecting rods requires more rod bearing clearance than engines with lighter pistons and ultra strong connecting rod. You have to look at all your components to determine what clearances are best for your application. If you lack the experience to make these critical determinations, I must advise you to consult an expert who has this experience.
Rear Bearing Clearance and Number-4 Main Failure
If you have measured the bearing clearances in the main journals, you know that the rear main (also known as number-5 main) has an extra .0010- to .0015-inch bearing clearance if the crankshaft mains are all ground to the same dimension. The rear shells are, by design, thinner radially than the first four shells. The GM factory initiated this design and the aftermarket bearing companies simply copied them.
I don’t know why the GM engineers gave that extra clearance to the rear main, but I can only guess that it is because of the additional width. I am absolutely convinced this additional clearance in the rear shells is the main reason for the notorious number-4 main bearing and number-4 main web failure. I have never seen a rear main wasted in an Oldsmobile engine, but I have seen plenty of number-4 main and main bearing failures.
If you think about what is going on here it makes perfect sense. If the rear main bearing clearance is .001 or .080 extra, and the rear of the crankshaft, which is attached to the flywheel, moves around as it starts to transfer power to the drivetrain, where do you think the load is transferred? You guessed it. It transfers the load to the next one in line, which is the number-4.
Chevrolet engines do not have additional clearance in the rear, and neither do Ford engines. In fact, most engines do not have that additional rear main clearance. The Oldsmobile is the only engine that has a notorious failure rate for number-4 main bearing shells and breaking blocks in the number-4 main webs.
You can easily fix this issue by simply machining the rear (number 5) main larger than the number-1 through -4 mains so that it takes the load. This is simple with undersize applications such as .010, .020, .030, etc. In crankshaft applications that have standard main journal sizes, the only way to help this situation is to purchase a main bearing set with .001 less clearance than you are working with and use the rear shell to tighten it up.
MAHLE Clevite manufactures a bearing set (PN MS 804 H-1) for big-block Oldsmobile applications that yields a .001 tighter clearance. In a typical standard-size main journal application, you can use the MS 804 H on the number-1 through -4 mains and use the rear shell from the MS 804 H-1 set to tighten the rear clearance by .001, which forces the rear journal to take the load off the number-4 main. You could also use the MS 804 HX bearings in numbers 1 through 4 to tighten the rear by .002 compared to the front four. With all of these shell choices, you can set the main clearance to whatever size you want if you cannot machine it.
One of the most important machining operations you will do in your high-performance Oldsmobile engine build is the preparation and grinding of the crankshaft. Forget shopping around for the cheapest price for a crank grind! Always remember, you get what you pay for. Every machining operation takes time and care. Just because you stick the micrometer on the journal in one spot and its dimension is what you intended, the grind job may or may not be suitable. I have seen many improperly ground crank journals on re-grinds and, shockingly, on brand-new crankshafts. A properly ground crank journal should measure exactly the same everywhere on that particular journal. With improper or no dressing of the crankshaft grinder wheel, you may see taper or out-of-round (different measurements) from one side of the journal to the other. This means that clearance is tighter in some spots and the oil wedge is improper, lacking two perfectly flat surfaces.
Bearing Clearances
The information below represents the minimum amount of bearing clearance, and should keep you out of trouble. When checking your bearing clearances at the time of assembly, don’t stress out if the actual measured clearance is more than anticipated. In the case of clearance, a little more is acceptable; any less is not.
The chart below is a reasonably accurate guide for people who have no means of properly measuring their clearances prior to assembly. The housing bore dimensions and the main bearing cap material both slightly affect the bearing dimensions. My experience is that the dimensions in these charts are within a few ten thousandths of an inch, and that amount is nothing to worry about. For those who feel they need to have bearing clearances within .0001 inch, simply measure your components. This data is for all for standard-size bearings; for use with undersized bearings, simply subtract that undersize dimension (.010 inch, .020 inch, .030 inch, etc.)
Small-Block Olds
Mains
| Main housing bore | 2.6870 inches |
| Uncoated bearing | Clevite MS805P |
| Dimension of bearing torqued in main housing bore | 2.5023 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.5000 | .0023 |
| 2.4995 | .0027 |
| 2.4990 | .0033 |
| 2.4985 | .0037 |
| 2.4980 | .0043 |
| 2.4975 | .0047 |
| 2.4970 | .0053 |
Mains
| Main housing bore | 2.6870 inches |
| Polydyne coated bearing | Clevite MS805P |
| Dimension of bearing torqued in main housing bore | 2.5010 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.5000 | .0010 |
| 2.4995 | .0015 |
| 2.4990 | .0020 |
| 2.4985 | .0025 |
| 2.4980 | .0030 |
| 2.4975 | .0035 |
| 2.4970 | .0040 |
| 2.4965 | .0045 |
| 2.4960 | .0050 |
Connecting Rod
| Rod housing bore | 2.250 inches |
| Uncoated bearing | Clevite CB684P |
| Dimension of bearing torqued in rod housing bore | 2.1273 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.1250 | .0023 |
| 2.1245 | .0028 |
| 2.1240 | .0033 |
| 2.1235 | .0038 |
| 2.1230 | .0043 |
| 2.1225 | .0048 |
| 2.1220 | .0053 |
Connecting Rod
| Rod housing bore | 2.250 inches |
| Polydyne coated bearing | Clevite CB684P |
| Dimension of bearing torqued in main housing bore | 2.1260 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.1250 | .0010 |
| 2.1245 | .0015 |
| 2.1240 | .0020 |
| 2.1235 | .0025 |
| 2.1230 | .0030 |
| 2.1225 | .0035 |
| 2.1220 | .0040 |
| 2.1216 | .0045 |
| 2.1210 | .0050 |
| 2.1205 | .0055 |
Big-Block Olds
Mains
| Main housing bore | 3.1890 inches |
| Uncoated bearing | Clevite MS804P and H |
| Dimension of bearing torqued in main housing bore | 3.0023 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 3.0000 | .0023 |
| 2.9995 | .0027 |
| 2.9990 | .0033 |
| 2.9985 | .0037 |
| 2.9980 | .0043 |
| 2.9975 | .0047 |
| 2.9970 | .0053 |
Mains
| Main housing bore | 3.1890 inches |
| Polydyne coated bearing | Clevite MS804P and H |
| Dimension of bearing torqued in main housing bore | 3.0010 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 3.0000 | .0010 |
| 2.9995 | .0015 |
| 2.9990 | .0020 |
| 2.9985 | .0025 |
| 2.9980 | .0030 |
| 2.9975 | .0035 |
| 2.9970 | .0040 |
| 2.9965 | .0045 |
| 2.9960 | .0050 |
Connecting Rod
| Rod housing bore | 2.6250 inches |
| Uncoated bearing | Clevite CB542P and H |
| Dimension of bearing torqued in rod housing bore | 2.5023 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.5000 | .0023 |
| 2.4995 | .0028 |
| 2.4990 | .0033 |
| 2.4985 | .0038 |
| 2.4980 | .0043 |
| 2.4975 | .0048 |
| 2.4970 | .0053 |
Connecting rod
| Rod housing bore | 2.6250 inches |
| Polydyne coated bearing | Clevite CB542P and H |
| Dimension of bearing torqued in rod housing bore | 2.5010 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.5000 | .0010 |
| 2.4995 | .0015 |
| 2.4990 | .0020 |
| 2.4985 | .0025 |
| 2.4980 | .0030 |
| 2.4975 | .0035 |
| 2.4970 | .0040 |
| 2.4965 | .0045 |
| 2.4960 | .0050 |
| 2.4955 | .0055 |
Small-Block Chevrolet
Connecting Rod (stroker applications)
| Rod housing bore | 2.2250 inches |
| Uncoated bearing | Clevite CB663 H |
| Dimension of bearing torqued in rod housing bore | 2.1023 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.1000 | .0023 |
| 2.0995 | .0028 |
| 2.0990 | .0033 |
| 2.0985 | .0038 |
| 2.0980 | .0043 |
| 2.0975 | .0048 |
| 2.0970 | .0053 |
Connecting Rod (stroker applications)
| Rod housing bore | 2.2250 inches |
| Polydyne coated bearing | Clevite CB663H |
| Dimension of bearing torqued in rod housing bore | 2.1010 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.1000 | .0010 |
| 2.0995 | .0015 |
| 2.0990 | .0020 |
| 2.0985 | .0025 |
| 2.0980 | .0030 |
| 2.0975 | .0035 |
| 2.0970 | .0040 |
| 2.0965 | .0045 |
| 2.0960 | .0050 |
| 2.0955 | .0055 |
Connecting Rod (stroker applications)
| Rod housing bore | 2.1250 inches |
| Uncoated bearing | Clevite CB745 H |
| Dimension of bearing torqued in rod housing bore | 2.0023 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.0000 | .0023 |
| 1.9995 | .0028 |
| 1.9990 | .0033 |
| 1.9985 | .0038 |
| 1.9980 | .0043 |
| 1.9975 | .0048 |
| 1.9970 | .0053 |
Connecting Rod (stroker applications)
| Rod housing bore | 2.1250 inches |
| Polydyne coated bearing | Clevite CB745H |
| Dimension of bearing torqued in rod housing bore | 2.0010 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.0000 | .0010 |
| 1.9995 | .0015 |
| 1.9990 | .0020 |
| 1.9985 | .0025 |
| 1.9980 | .0030 |
| 1.9975 | .0035 |
| 1.9970 | .0040 |
| 1.9965 | .0045 |
| 1.9960 | .0050 |
| 1.9955 | .0055 |
Big-Block Chevrolet
Connecting Rod (stroker applications)
| Rod housing bore | 2.3250 inches |
| Uncoated bearing | Clevite CB743 H |
| Dimension of bearing torqued in rod housing bore | 2.2023 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.2000 | .0023 |
| 2.1995 | .0028 |
| 2.1990 | .0033 |
| 2.1985 | .0038 |
| 2.1980 | .0043 |
| 2.1975 | .0048 |
| 2.1970 | .0053 |
Connecting Rod (stroker applications)
| Rod housing bore | 2.3250 inches |
| Polydyne coated bearing | Clevite CB743H |
| Dimension of bearing torqued in rod housing bore | 2.2010 inches |
| Crankshaft Main Journal | Main Bearing |
| Dimension (inches) | Clearance (inch) |
| 2.2000 | .0010 |
| 2.1995 | .0015 |
| 2.1990 | .0020 |
| 2.1985 | .0025 |
| 2.1980 | .0030 |
| 2.1975 | .0035 |
| 2.1970 | .0040 |
| 2.1965 | .0045 |
| 2.1960 | .0050 |
| 2.1955 | .0055 |
The second area of concern is surface finish. You cannot have a crankshaft journal too flat or too smooth. A common procedure is to rough grind the journal and then superfinish it until it is smooth. You have to be very careful when superfinishing because the abrasive belt typically removes more material in the center of the journal and less on the ends.
Do yourself a favor; don’t shop around for this operation. You get what you pay for. Find a good crank grinder who is easy to deal with and pay him for his time. Typically, if you have a conversation with the crank grinder and let him know that you are willing to pay for the extra time spent on a quality job, it is usually received very well. And he will be very happy to spend the extra time required to give you a high-quality grinding job. The extra expense is usually pennies when compared to the consequences of engine failure.
One of the most popular Oldsmobile performance modifications is to increase the stroke of the crankshaft. This increased stroke not only increases the cubic inches of the engine, but has a few other advantages.
In general, an engine with increased stroke makes more torque at a lower-RPM range, which makes this modification ideal for high-performance street engines. More torque and horsepower in the lower-RPM ranges allows the use of tighter torque converters and low-numerical gears, which makes this modification a popular choice for high-performance street cars. I have not seen an engine yet that didn’t like to be larger. An increased stroke makes more average horsepower and torque throughout the RPM range. I have never seen that to be a negative thing, whether it is a street engine or a race engine. Another advantage is that the rod-journal diameter is reduced, which allows the use of more popular (available and less-expensive) Chevrolet connecting rods, in addition to reduced friction and less weight.
This finished 3.750 destroked 425 crankshaft is knife-edged, balanced, and, with reduced-diameter counterweights, ready to be bolted into Greg Finnican’s 394-ci DX Olds small-block.
This procedure is done to the crankshaft by changing the rod-journal diameter to that of a smaller-diameter engine (usually the common Chevrolet). By removing the material on the part of the rod journal closest to crankshaft centerline only, instead of removing the material all the way around, the stroke of the crankshaft is increased. The stroke is increased by the amount of material you remove from the bottom of the journal.
An example of a typical stroker Oldsmobile crank is a 455 big-block. The factory stroke is 4.250 inches, and the rod journal is 2.500 inches in diameter. If you want to increase stroke by .250, giving the crankshaft 4.500 inches of stroke, the rod journal is reduced by at least .250 inch. When stroking the 455 nodular-iron crankshafts to 4.500 stroke with the big-block Chevrolet 2.200 rod journal, they seem to have a problem with flexing at horsepower levels around 700, as I learned in the 2009 Popular Hot Rodding [PHR] Engine Masters Challenge. After two crankshafts wiped out the number-2 and number-4 main bearing on the dyno, it was pretty clear that the crank just wasn’t going to handle it. I know for sure there is a problem with flex at the 700-hp level, but I have several successful builds at 600 hp.
