Before you start purchasing parts, find out what needs to be replaced and what can be used again. Not everyone is going to replace everything in the engine, so if you are replacing all the internal parts for new ones, you can skim through this chapter to pick up some knowledge and move on to the next chapter. If you are purchasing used parts to replace the ones coming out of your engine, you can use this chapter to assist you in making good purchases.
This Tech Tip is From the Full Book “HOW TO REBUILD THE BIG-BLOCK CHEVROLET“. For a comprehensive guide on this entire subject you can visit this link:
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Step 1:Inspect Bearings(Critical Inspection)
The bearings tell a lot about what your engine has been through. With normal wear, the bearing wear should be fairly uniform from front to rear. Uniform brass material exposed is common, but these bearing shells show brass spots, which are from debris trapped under bearings before assembly. Tiny debris can make a big difference. Slight scoring or gouging in the bearing surface is usually caused by loose debris making its way past the filter and into the bearings. Deep tears in the top layer and dark coloring is usually caused by lack of oil pressure. Stamping on the backside tells you if your engine may have been rebuilt before; Delco or Moraine stamps are a good sign of rebuilding. If your journals don’t have a “.010-inch,” “.020-inch,” etc., stamp, they are most likely still stock size. A “.010-inch” stamp on a main bearing means it’s for a .010-inch undersized crank journal.
Step 2:Inspect Intake Manifold (Critical Inspection)
If you are going to use your original cast-iron intake manifold, inspect it for cracks in the carb mounting flange and intake ports. If your engine has a short water pump check, make sure the alternator boss in the front is in good shape. Check the water jacket ports and thermostat housing mounting boss and threads for severe rust and erosion.
Step 3:Remove Oil Splash Shield
Do not skip this step if you’re going to use your castiron intake. During a rebuild, always remove the oil splash shield that keeps oil from splashing on the hot EGR crossover from under the intake. The amount of hard carbon deposits under the shield depends on the mileage of the engine. Clean the intake in a hot tank or pressure wash only; do not sand blast because the media can get trapped and damage the engine later.
Step 4: Replace Intake Manifold Rivets
Replace the rivets with small Allen-head screws. Tap the holes that hold the shield in place, then install the screws with a drop of Red Loctite to keep them from coming loose and falling onto the rotating assembly.
If you plan on using the same camshaft and lifters in your rebuild, you have to keep them in order so you can put them back in the engine the same way they came out. The cam and lifters “wear” to each other, so this order is critical. Each cam lobe face should be flat and their measurements should all match. The lifter faces should all be completely flat and smooth, unlike the lifters shown here. If you have a hydraulic non-roller lifter cam, set each lifter on a flat wooden surface, push a pushrod into the cup, and make sure each of the lifters compress under an equal amount of pressure. If your cam or just one of your lifters doesn’t pass the inspection, you must replace the cam and lifters.
Step 5: Verify Pushrod Trueness
Check a pushrod for straightness by rolling it across a flat surface, preferably a piece of glass. A slight bend will be obvious as you roll it. Replace any pushrod that is not completely straight. If you are going to use your original pushrods, you need to keep them in order and put them back with the correct cylinder. Visually inspect the rocker arm for abnormal wear in the fulcrum socket; the rocker tip should be smooth, not grooved like the tip of this rocker.
Step 6: Inspect Block for Cracks
Inspect for visible cracks over the entire surface of the block including the cylinder walls. The machine shop does a more precise inspection if you opt to have them leak check and Magnaflux the block and heads. Your inspection could save you money if you detect a bad block. Carefully inspect your lifter bores with a light and your finger to make sure the surfaces are free of burs and grooves. Check the deck surface around the cylinders for possible grooves caused by failed head gaskets. Glance at the threads to make sure they aren’t stripped. Make sure there aren’t any chunks of block missing around the transmission mounting holes and starter.
Step 7: Check the Block for Sleeves and Other Problems
A sleeve doesn’t necessarily mean that the block is junk. This block has a sleeve installed. Closer inspection showed signs of coolant leaking into the crankcase at the base of the sleeve and that a small crack was present. It’s obvious; a good shop did not do this work. This sleeve would need to be machined out and replaced. After weighing the cost of repairing it, this block was discarded.
The main caps should fit tightly in the block registers. If you have a dial bore gauge, you can re-install the main caps and check for outof- round main bores from excess stress caused by detonation. Also run that gauge in the cylinder bores for out-ofround bores. The machined boss on the face of the block behind the cam sprocket should be smooth. If it’s different, the timing chain set uses a bearing plate (shown). Check for chips on the web at the bottom of the cylinder bores usually caused by a previous failure or by knocking the rods into the block upon disassembly.
Step 8: Replace or Rebuild Oil Pump Pickup (Critical Inspection)
It’s typical to replace the oil pump but to reuse the oil pump pickup. If you are going to reuse the pump, it needs to be rebuilt (see Chapter 8 sidebar, “Oil Pump Checking and Modifying”). The oil pump pickup has a screen on the underside and it should be in good shape. If the pickup is mangled in any way, replace it. If the pickup has been welded to the pump, you should consider replacing both because you have no assurance the person who did the welding didn’t damage the oil pump in the process. The oil pump mounting surface on the rear main cap should be smooth and the oil pump should fit tight in the two dowel pins.
Step 9: Inspect and Clean the Head Gasket Surface (Professional Mechanic Tip)
Clean the head gasket surface so you can inspect it. Don’t gouge the surface. At a slight angle, lightly scrape the surface with a razor blade scraper (this is a good method for all gasket surfaces). Check for divots or grooves leading away from the combustion chambers (caused by head gasket failure); if present, the head and the block may need resurfacing.
Step 10: Inspect Valves
If you had to file a valve to remove it from the head, you should replace the valve and the locks. Build-up of carbon on the backside of the valve is a sign of oil getting into the intake port by way of a worn valve guide or a leaky gasket under the intake manifold. The valve on the left shows signs of “peppering” on the sealing surface because the seats are original; they have not been upgraded for use with unleaded fuels.
Step 11: Check the Crankshaft (Precision Measurement)
A few quick checks indicate the condition of your crankshaft. The crank key should be a tight fit in the keyway. There should not be a deep groove in the journal where the rear main seal rides. The thrust flange on the crank should be flat and smooth to the touch. Check the size of the crankshaft journals with your micrometer. Dark spots or deep scoring on the journals are bad signs. If your crank is more than .030 inch undersize or if your crank doesn’t pass these initial inspections, you need to start shopping for a new one.
Improper balancer installation could have damaged the threads in the front of the cranks, so check these threads. Also check the threads in the flange on the back of the cranks where the flywheel or flexplate mount. If your crank has one, remove the pilot shaft bushing and install a new one later if you have a manualtransmission- equipped vehicle.
Step 12: Check Flex-plate for Damage
The flex-plate should be free of cracks. They typically crack around the area that bolts to the crank. The flywheel friction surfaces should not have deep stress cracks. Sometimes you can resurface a flywheel and save it; if not, get a new one. Your flex-plate or flywheel should be inspected for missing or chipped teeth; replace it if you find any. These are slightly chipped and could cause problems in the future.
Step 13: Inspect Pistons(Critical Inspection)
Make sure the pistons don’t have any excessive skirt wear or cracks, including around the wrist pin. The piston rings shouldn’t be locked into their grooves. If they are, and carbon build-up is not the cause, it’s possible the piston needs to be replaced. Clean the carbon out of the grooves and check fit again. The face of the piston should be free of holes, gouges, and marks that look like pools of molten aluminum. The rods should not be bent or twisted. They should not be severely discolored around the bearing end. If your engine was rebuilt, make sure the rods are number stamped “1” through “8.” If your pistons or rods don’t pass, you can simply replace the ones you need and have them matched to the good parts.
Step 14: Inspect Harmonic Dampers (Critical Inspection)
Harmonic dampers are wearable items. Check your damper’s rubber ring between the hub and outer ring. If the rubber shows signs of cracks, distortion, or misalignment, it’s time to replace it. When they fail, the outer ring can slip on the hub causing the timing mark to move and also cause bearing-damaging vibrations.
Step 15: Harmonic Damper Repair
The seal in the timing cover can wear a groove in the harmonic damper. Victor-Reinz makes a repair sleeve that simply presses over the hub and turns a leaky damper into a useable unit.
Machine shops typically have many engines apart at the same time that yours is in their possession. Use a number stamp like these. These are used for numbering rods. Use these, a center punch, or an engraving tool to distinctively mark all the parts you plan to take to the machine shop so there are no accidentally swapped parts while they are out of your hands. Mark the rods on the flat surface near the rod bolt.
Your engine is disassembled and you are ready to start the visual inspection. Wear patterns and defects in the parts tell a story of what’s been going on inside the engine and why it’s being rebuilt. Different types of failures leave different types of damage. There are all types of failures including: loss of oil pressure; foreign objects entering into the intake manifold; internal parts failure due to overrevving or using parts not designed for your driving style; overheating; freezing; and, head gasket failure.
Each type of failure requires a different repair. If your engine suffered from a head gasket failure or if you suspect it, there are some tell-tale signs to look for. When a head gasket fails, the water escaping the coolant passage or compression leaking out of the combustion chamber can cause pathways or grooves in the head gasket surface of the block and heads. These pathways are typically found between two cylinders or between a coolant passage and one cylinder. If these pathways exist, the block and head can be resurfaced to eliminate the groove. Machining these surfaces can lead to intake manifold fitment and piston-to-valve clearance problems. The machine shop will make a determination on fixing this problem or if other components need to be sourced.
Inspect the parts and follow the clues they leave in order to approach repairing the engine or rebuilding it. Every engine and part has a different story to tell.
Inspecting your parts is an important step. If you find visual damage on your parts before going to the machine shop, you can save yourself some money by not paying them to do the same thing. The damage that’s harder to find, like fractures or small cracks, will be caught at the machine shop. If you see a crack in your block on any surface other than the cylinder, you should consider replacing it unless it’s a numbers-matching block on a rare car. In the case of saving a severely cracked block, you should contact your machine shop and determine your options. Saving a rare block after it has been cracked from rotating parts failure or from a frozen cooling system is a dying art. Most machine shops don’t do more than sleeve them. A crack in a cylinder is repairable as long as the crack hasn’t traveled into the main cap web or too far up to the deck surface.
Check the block for wear and cracks in the cylinders. If the cylinders don’t appear to have any significant wear, you probably don’t need to waste much time looking for cracks. If you notice a ridge about a quarter inch below the deck surface, such as the one seen in this chapter, your block should go under some close scrutiny to determine if it can be bored far enough to eliminate the ridge. If the cylinders do have significant wear, the machine shop will need to determine the fate of the block.
Once your heads are disassembled, you will have a clear picture of their condition. When removing the valves, you know if they had a ridge you needed to file down and might have noticed if they felt loose in the guides when you took them out. Give the entire casting a once over and look for visible defects, which include worn valve guides, damaged threads, deterioration around the coolant passages, chunks of material missing, or cracks in any part of the casting.
If you see cracks or divots in the head castings’ combustion chamber area, your engine might have stopped working because a foreign object made its way into the cylinder or a valve was dropped. I’ve seen a carburetor base-plate screw fall into an engine and cause three bent intake valves, one bent exhaust valve, a damaged head, a cracked block, and a collapsed piston. The screw bounced around to three different cylinders before getting past one valve completely where the real carnage took place. I’m sharing this to relay that damage in one cylinder can also mean that other cylinders should be checked for problems.
Get your micrometer out and start checking the journals of the crankshaft. Check for any deep scratches and to see if the crankshaft has already been ground too far. The size of the rod journals should not be less than 2.17 inches and the main journals should not be less than 2.72 inches. If they are, consult your crank grinder. After all is said and done with the crankshaft machining, you don’t want to use it if it has been ground more than .030 inch from original; it’s not reliable enough to use. If you notice dark spots on the journals or if one journal is noticeably darker than the others, it’s possible a bearing failure caused that journal to soak up some extreme heat and should be replaced.
Replace connecting rods that show signs of being bent or twisted. A bent rod is not always apparent upon visual inspection. Uneven wear patterns on the piston is a sign of possible problems with the connecting rod it’s attached to. The machine shop needs to make more in-depth inspections of them when they are reconditioning them. As with the crank, if your connecting rods have a darker bearing end than the wrist pin end or one rod is visibly darker than the others, it’s possible that a bearing failed and it severely overheated the rod and could have fatigued it to the point where replacement is necessary.
Inspect the harmonic damper for visible cracks in the keyway or any part, a worn-out seal between the hub and the outer ring, and a groove in the hub where the seal in the timing cover meets the damper hub. Any cracks in the metal or a worn band between the hub and ring are signs that you need to replace the damper. A groove worked in by the timing cover seal can be fixed with a repair sleeve.
Written by Tony Huntimer and Posted with Permission of CarTechBooks