You may think that taking time to inspect engine components right after disassembly isn’t necessary. After all, you’ll be paying your machine shop to inspect and recondition your engine with the latest, high-tech equipment. They’ll find anything wrong before money is spent on machine work, won’t they?
Before the Machine Shop
In the best of all possible worlds, machine shops never make mistakes. However, in this world, machine shops do, and there can be some question about who is ultimately responsible. If you don’t know that it’s right, presume that it isn’t. When you’re knowledgeable about all aspects of your rebuilding project, it will likely succeed with flying colors.
This Tech Tip is From the Full Book “SMALL-BLOCK CHEVROLET: STOCK AND HIGH-PERFORMANCE REBUILDS“. For a comprehensive guide on this entire subject you can visit this link:
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This chapter will help you inspect the main components of your engine before you take them to the machine shop—before any money is spent on reconditioning. The following inspection steps are not meant as a substitute for comprehensive testing with precision equipment. Rather, this summary inspection (requiring some precision tools) will give you sufficient familiarity with your components to speak knowledgeably with your machinist. At best, you’ll find nothing outside of the ordinary; at worst, you’ll come across one or more pieces that are damaged beyond repair. A real advantage of the small block Chevy is that you can easily obtain replacement parts, and most are reasonably priced. Even major components such as engine blocks and crankshafts probably won’t break your budget. Information about replacement “cores” and their approximate costs followat the end of this chapter.
A very in-depth component inspection will be done in Chapter 7, “Pre- Assembly Fitting,” after all the parts have been reconditioned by your machine shop. Remember, the more critical your eye, the less money you’ll spend on your engine building project.
What To Do When Your Parts Don’t Pass Inspection
The old saying “anything can be fixed” is nearly true. However, it should read, “anything can be fixed for a price.” Unless you have a defective part that is very rare and cannot be replaced, it’s much cheaper to have your machine shop obtain a replacement core or a new part from the aftermarket and continue with the work.
If you purchase a core from your machine shop, you’ll pay slightly more than from a typical wrecking yard. Despite this, it’s generally preferable to purchase cores from the shop doing most of your machine work. Why? When you take into consideration that a machine shop may buy a large number of used blocks, heads, or cranks, clean them, inspect them, test them, and then findout a certain number are junk, you soon realize that there’s more to buying usedparts than meets the eye. On the otherhand, if you purchase a core from awrecking yard, there’s usually some question whether it’s even returnable, and even if you can return it (haggling at the front counter not withstanding), you’ll have spent a considerable sum of (nonrefundable) money on cleaning, inspection, and testing. So spending a bit more for a “guaranteed core” from your machine shop makes a lot of sense. However, if you decide to buy parts from a wrecking yard, make sure you establish that defective merchandise can be returned before you write the check.
A typical engine overhaul may require one or more of the following replacement cores.
Blocks. Cores will run anywhere from $100 to $250. If you’re looking for a special, hard-to-find casting, expect to pay much more for a dirty, unmachined piece.
Heads. Cores run about $50 to $100 per head. Remember, it’s almost always cheaper to replace a cracked head than attempting a repair, especially with today’s aftermarket. Common “882” castings are not the best head but are acceptable. “624s” are a very thin-wall design and should always be avoided, even for streetstock applications. “186” or “041” castings, at about $100 to $200 per pair, are probably the best replacement castings per dollar spent. These heads were made in late 1969 and 1970, came on 300-hp 350s, used 1.94/1.50 valves, have small chambers, straight plugs, and good flowing ports. Despite the fact that they were made for only two years, we have it on reputable word that there are “a million of ’em” still around. Also consider the late-model, 4-bolt (valve cover) heads. They’re about three pounds heavier than earlier factory designs, making them less prone to cracking, plus they’re plentiful and cheap. There are now a variety of bare and complete heads available from the aftermarket that may offer increased metal in vital areas, and often have better flowing ports. In some cases, these may cost a little more, but in the long run, after machining costs, and new components, you may end up with a better head at the same cost. In all cases, make sure the chamber volume is compatible with your pistons; some 305, small-chamber heads (available everywhere) have under 60 cc and can easily develop 11:1 with flat-top pistons.
Cranks. When choosing a cast-iron replacement crank make sure it has the correct counterweight pattern (305 and 350 have the same stroke and journal size, but the factory balance is greatly different). Steel cranks are just about impossible to find at wrecking yards and machine shops. You might as well buy a new steel crank from GMPP or other aftermarket company for about $200 to $700.
Rods. Rods are a few bucks each. Many machine shops supply cores at no charge to their good customers.
Valves. Used valves will also be inexpensive, but don’t even consider them. Clearances (angles and tight tolerances) and different applications produce too many variables. Go with a new set!
Vibration Damper. Replacement cores run about $35. New ones can range from $100 and higher. If you need a damper for performance or racing, consider a Fluidampr a high-performance unit from B&B Performance.
Flywheel and Flexplates. Flywheel cores run about $50 and will need to be resurfaced. Depending on the condition, a new one may be worth the cost, especially if you’re planning on a performance engine. If you’re replacing the flexplate, make sure to get one with the correct number of gear teeth! Same goes for the flywheel.
Other Cores. EGR (exhaust gas recirculation) intake manifolds are very hard to find (just about all factory manifolds are cracked). Legal replacement manifolds are available from many aftermarket companies, including Edelbrock, Holley, Weiand, etc. These intakes are considerably lighter than the stock cast iron ones and often will flow better for improved performance. Prices generally start just over $140 for new ones, or hit a swap meet to find a used one.
Unless you’re knowledgeable about component interchangeability, discuss cores and replacement parts with your machine shop before you buy. Remember, the quality of your engine is truly the sum of its parts!
Initial Parts Inspection
Step-1: Begin Cylinder Block Inspection
Every engine has its own “personality.” Here are a few common problem areas on the small-block (a high-intensity light, such as the one used here from Snap-on Tools, is very helpful). First, inspect the valley area for water jacket cracks. They sometimes run horizontally, just above the lifter bores. Cracks also occur on the outside of the block, just below the deck surfaces. Check the decks for cracks or combustion-gas gouges from blown head gaskets. Check all threaded holes for stripped threads or cracking, including the oil-pump mounting hole on the rear-main cap. If the engine was purchased from a junkyard, look over the exterior of the block for damage, like broken off chunks (especially around starter mount), etc., and have the block Magnafluxed and pressure-tested.
Step-2: Continue Cylinder Block Inspection
Check that the main caps fit snugly in their recesses on the block. The parting edges between the cap and the block bores should line up and be smooth to the touch (if they aren’t, the caps may have been switched). Inspect the camshaft upper-sprocket thrust face for gouges. If you have access to precision measuring tools, mic the cylinder bores, check the main bores for proper size and out-ofroundness (block may need align boring—many small-blocks do), and mic the lifter bores to make sure none are worn or oversize. Finally, look for any cracks in the bottom end, particularly at the bottom of the cylinder bores (from previous improper disassembly techniques), around the main bolt-holes (from excessive over tightening of the bolts), and in the main webs (often due to excess stress from detonation).
Step-3: Cylinder Head Inspection
Cylinder heads, particularly late-model castings, are weak points. It is not uncommon to find cracks in the valveseats, bolt holes, exterior surfaces, and elsewhere. Some factory castings are so prone to cracking they should be avoided. Probably the worst of all is the 624 head (“624” refers to the last three casting numbers—462624—located over or under two of the intake ports). If your engine has these heads, consider scrapping them and finding replacements. Possible replacements are the 882, 487, 493, 993, 545, and others. Ask your machine shop for help in selecting replacements (make sure they have the accessory mounting holes needed for your application).
Step-4: Continue Head Inspection
Continue looking for cracks in the valve seats, across the lower row of bolt holes, and in the exterior parting line across the centerline of the exhaust ports. You may find evidence of previous weld repair work, since about 25 percent of all small-block heads have small repair spots from the factory. GM does a nice job on these “touch ups,” and repaired heads should not necessarily be tossed aside. Look for eroded valveseats and head surfaces between chambers. Inspect the valves for stem, lock groove, tip, and face wear. Also, look for hairline cracks across the face and head. Check for excessive guide wear by wiggling the valves in the guides. Examine the rocker studs for looseness, damaged threads, or side wear from rocker arm contact. Look over the spring splash shields for wear.
Step-5: Inspect Crankshaft
Remarkably, about 50 percent of all small-block cranks are reusable directly after cleaning and polishing. Unfortunately, some cranks may look fine at first glance but turn out to be unusable. Here are the common things that can turn your crank into scrap metal. Check the crank thrust surface by running your finger over the thrust flange. It should be smooth and perfectly flat. Check the key ways on the nose; they should not be enlarged and the keys should fit snugly. Mic the journal diameters; they should not be more than .030 inch under size or look badly discolored. Inspect the rear seal surface; it should be smooth and have no annular grooves. If your crank doesn’t pass these initial tests, consider obtaining a replacement from your machine shop.
Step-6: Continue Crank Inspection
Continue inspecting the crank by looking for some less-serious problems. Inspect the flywheel flange and crank nose for damaged threads (this thread-chasing tool set from Snap-on, part RTD42, cleans threads without reducing thread strength). Look at the rod side-thrust faces on each rod journal; they should be smooth and have no discoloration. Finally, if you’re going to be using a manual transmission, make sure the crank has a pilot bushing installed (or that it’s machined to accept one). This Snap-on puller kit (part YA6100) removes old pilot bushings from just about any crankshaft. Finally, the crank should be Magnaflux-inspected by your machine shop. If your engine is out of a car with a manual transmission, make sure to remove the pilot bearing from the crankshaft (and be sure to install a new one). Snap-on and other companies offer a puller tool, or you may be able to remove them yourself with a screwdriver or grease gun.
Step-7: Inspect Rod/Main Bearings
Inspect the main and rod bearings for excessive wear. Signs of poor lubrication or dirty oil will show scores or light scratches. If there is other engine damage you may see metal particles embedded into the bearing material. Discoloration indicates inadequate oiling or excessive heat. These two rod-bearings show signs of detonation. Also, look on the back of the bearing for signs of excessive loads or detonation. While you’re looking, there may be numbers such as “.020” that indicates the bearing is .020 inch oversized meaning that the crank has been turned prior.
Step-8: Inspect Rods and Pistons
Make sure the rods and pistons are all the same type. If the engine has been previously rebuilt, it’s possible you may find an oddball rod/piston or two, and if the weight is different, the engine may have had an out-of-balance vibration. Inspect the piston skirts for uniform wear patterns; canted or twisted patterns indicate a bent rod. Check the big-end inside diameter for roughness or discoloration (probably due to a spun bearing—rod may not be rebuildable). If you have the necessary precision tools, check the big-end bore for correct size and out-of-roundness. Mic the width of the rods and compare them to the width of the crank throw; clearances should be between .005 and .012 inch for most applications.
Step-9: Continue Rod/Piston Inspection
If your cylinder bores have almost no detectable wear and you’re planning on reusing the pistons, mic the outside diameter (usually at the bottom of the skirt) to verify that none of the pistons have “collapsed.” Check the width of the ring lands (they should have no more than .003 inch clearance with a new ring—measure using a feeler gauge), and give the pistons a careful visual inspection. Have your machine shop clean and test them for proper pin fit, piston-to-cylinder wall clearance after honing, and piston/rod alignment. As with the crankshaft, cracks in the rods and pistons are almost impossible to find with the naked eye. You may want to ask your machine shop if it would be more expensive to have all the rods Magnafluxed compared to buying a new set. Your choice.
Step-10: Inspect Camshaft and Lifters
Chances are that you are going to replace the cam and lifters for an improved set. The only time the cam and lifters are reusable is: 1) when all the lifters have contact surfaces that are smooth and uniform in appearance, with a slight crown [A], not a concave shape [B], 2) the lifters have no detectable outside diameter wear, 3) all the cam lobes show no signs of galling or excessive wear (mic the lobe heights to verify lack of wear), 4) the distributor-drive gear teeth on the cam show no significant wear, 5) the lifters have been organized so that they will be reassembled in exactly their original position, and 6) the cam and lifters will be reassembled into the same engine block. If you have one of these rare small block cam and lifter sets that pass all these tests, you can reuse the camshaft. Oil the cam and lifters and wrap them in wax paper to prevent rust during storage.
Step-11: Inspect Oil Pump and Pickup
Most engine builders reuse the oil pickup but replace the pump. Refer to Sidebar “Oil Pumps: Blueprinting and Modifying” on page 44, for inspection, rebuilding, and performance modifications. Check the pickup/screen carefully for damage. Look for cracks in the tubing seam, especially where it enters the pump cover. Make sure the wire screen is not loose or plugged with debris; the pickup should get a thorough soaking in carburetor cleaner before reuse. Finally, inspect the oil pump and rear main cap mating surfaces; no gasket is used between the oil pump and the main cap, any damage to these surfaces will result in high-pressure oil leaks.
Step-12: Inspect Oil Pump and Pickup
The vibration damper can become worn or damaged in several areas. First, make sure that the keyway in the hub is not enlarged. Check the pulley-attaching threads (if damaged, they can be Helicoil repaired), and make sure the rubber is not working out from between the inner hub and the outer damper ring (if it’s oozed out even slightly, consider replacing the damper). If possible, put the damper in a lathe and measure how much it wobbles; the maximum is about .020 inch. Finally, check the hub oil seal surface for a grooving that can lead to an oil leak. The contact lip on all replacement seals is moved inward, so if the hub groove is shallow, the new seal will ride on an undamaged surface. If the groove is deep, a slide-on metal sleeve is available; it can be used with factory or replacement front seals.
Step-13: Inspect Intake Manifold
Many factory small-block manifolds have a heat shield riveted under the riser passage. Hard carbon deposits build up under this shield; it must be removed before the manifold is hot tanked or jet washed. A small chisel and light hammer taps will usually work the rivets out. Inspect the riser passage for heat cracks. If the manifold is equipped with EGR (exhaust gas recirculation), carefully inspect the plenum for cracks running down between the large throttle bore. EGR manifolds get very hot, and cracks in this area are quite common. Finally, inspect the manifold-to-cylinder head surfaces for cracks, erosion from rust, or other damage.
Step-14: Mark Your Parts
This completes the initial inspection of major engine components. If any of your parts did not pass inspection, refer back to page 48. Regardless of the outcome of your inspection, put your own individual mark or stamp on every part before you take it to the machine shop. Use a number stamp, center punch, or an engraving tool, and mark only on non-machined surfaces. Identifying your parts will prevent possible mix-ups and disagreements in the future.
Written by Larry Schrieb and Posted with Permission of CarTechBooks