Rebuilding a Chevy Straight Six Part 2
Section 2: Disassembling the engine
In our last issue we began a series on engine rebuilding using a 1957 Chevrolet six cylinder as our example. When we left off, we had pulled the engine from the car, removed the manifolds, carburetor and head. We also had disassembled the rocker arm assembly, removed the pushrods and hydraulic lifters and examined all the parts for wear. During the teardown process, we noted heavy ridges at the tops of the engine’s cylinder bores, indicating that it will probably need to be rebored.
In this installment we will concentrate on the bottom end of the engine, which consists of the crankshaft, connecting rods, pistons, cam and timing gears. Many engines have timing chains as well as timing gears, but the Chevy six has only the meshed timing gears.
To begin disassembly of the bottom end of the engine, turn it over on your engine stand so the oil pan is up. Be prepared for a little oil and coolant to run out onto the floor from hidden nooks and crannies in the block.
Loosen the pan bolts, working from the center of the engine out to the ends. Note that there are four larger bolts securing the pan around the front and rear main bearings. When all of the bolts are out, slip a putty knife under the pan and pop it loose. Often, on engines that have been in service for a long time or with those that have been neglected, you will find a great deal of sludge in the pan. If you do, scrape it out and dispose of it properly according to local environmental laws. I usually put engine sludge in an old paint can and set it out next to the trash on special days when the city picks up toxic materials. Your area may have different procedures.
The oil pump comes out next. Disconnect the pipe that connects the pump to the block, but do not attempt to remove the mesh filter and pickup tube on the Chevy six pump. These are installed at the factory and are not intended to be disassembled. Down in the block is a setscrew and nut that holds the pump in place. Loosen the nut, then remove the setscrew. Now pull the oil pump out, wash it with solvent, disassemble and inspect it. Is the pump body cracked or worn? Are the gears worn or damaged? Is the shaft loose in its housing? Check the inside of the cover to determine excessive wear. It should not allow oil to leak past the ends of the gears. Also check the regulator valve plunger. Inspect the screen in the oil pickup unit. Is it torn or damaged? If so, replace it. If problems other than a torn screen exist, you will need to obtain a rebuilt pump, because these items are not rebuildable by the home mechanic.
You can obtain a rebuilt pump from an antique parts supplier such as Egge Machine in Santa Fe Springs, California. Egge will be the source for most of our components on this project (see info below on Egge).
The next challenge will be to remove the harmonic balancer from the front of the engine. The manual says to use Chevrolet tool 1287, but an ordinary gear-puller will remove it just as easily. Generic gear pullers come with an assortment of bolts for different applications. For this project we selected two 3/8-inch x 16 bolts of the correct length and put them through the appropriate holes in the puller, then into the holes on the front of the balancer. Make sure you tighten them enough to avoid having them pull out and strip the threads in the balancer when you tighten the puller. Also make sure you tighten them evenly so the crosspiece of the gear-puller is parallel to the gear. Otherwise you will pull on the gear at an angle and possibly cause some damage. Now tighten the puller slowly until the harmonic balancer pops off. Be careful – it may come off with considerable force.
Remove the timing gear cover by loosening all of its screws evenly, then removing them. Note that, on the Chevy six there also are two bolts that attach from the back of the cover through the front main-hearing cap. Save the screws and bolts in a labeled coffee can or jar. Next remove the smaller crankshaft timing gear using the same gear-puller as you used for the harmonic balancer or if you just happen to have a set of those special Chevrolet engine tools use number 8105 which will do the same job in the same manner.
Turn the large fiber camshaft gear until the holes in it line up with the screws that hold the camshaft thrust plate in place. Insert a screwdriver through the holes and remove the two camshaft thrust plate screws. Support the cam at the back of the engine with one hand so it won’t damage its bushings on the way out, and then carefully slip the cam out the front of the engine. The cam lobes and bearing surfaces should be shiny and free of grooves or evidence of wear. If the cam is seriously worn, it will need to be replaced. When it’s time to take the engine components to the machine shop, the cam will need to be more carefully checked for wear with a micrometer, then Magnaflux tested to check for cracks. It should also be straightened if necessary.
Never lay a cam, or crankshaft, on its side when storing it. If you do, there is a good chance it will warp from its own weight. Stand the cam on end using the timing gear as a base. Strap it to a post in your garage using coat hanger wire to keep it from being knocked over. Chevy cams are long and are made of cast iron alloy, so they can crack, or even shatter, if dropped. The crankshaft also must stand on end and should be supported by wiring it to a vertical framing joist or post in your garage.
Before removing your engine’s pistons and connecting rods, mark them with a file or punch so you can remember their cylinder number and positioning in the cylinder. Most pistons were made of comparatively soft aluminum by 1957, so marking them is easy but requires some care on your part. Gently tap the punch when stamping in the identifying numbers to avoid any damage. (The usual procedure is one dot for the number one piston, two dots for number two, etc.) Also make sure you punch all numbers in the same location on the piston, so you will know which way the piston is supposed to face when reinstalling it. The future usefulness of your old pistons however will depend on the overall condition of the engine. If your engine is worn and requires reboring (as is often the case) you will have to install new oversized pistons to fit the larger bore.
To conveniently work on the connecting rods and crankshaft, turn the block upside-down in your engine stand. Number the connecting rod end caps as you did the pistons using a punch or small file. Each connecting red end cap must go back on the same rod and be placed so it’s facing as it did originally. If you need to turn the crankshaft while working shoot a little light oil onto the cylinder walls then try to turn it with your hands. If you cannot move it use a piece of wood to pry against the balance weights to move it.
When I go to the trouble of taking an engine apart I usually rebuild it completely although doing so is not always required. If your engine had good oil pressure before you tore it down, the rod and main bearings may not be badly worn and it’s not absolutely necessary to replace them. Inspect them for wear, pits, scoring, galling or other damage, and if they appear to be in good condition, you can further check their clearances with Plastigage. This product is available at auto parts stores, and consists of a tiny plastic rod inside a paper envelope. To use it, merely place a bit of the plastic on the crankshaft journal, then torque the rod bearing cap into place. (The torque Specification on a ’57 Chevy six is 35 to 45 lb.-ft.)
Do not turn the crankshaft with the Plastigage in place, as it will distort your reading. Now remove the bearing cap and use the accompanying paper to check the bearing’s clearance. If it is between .001-inch and .004-inch, the clearance is still satisfactory provided the Plastigage is flattened evenly. If the squashed plastic is wider at one end than the other, your crankshaft may be worn. If the clearances on your rod bearings are greater than .004-inch they are too loose and will not hold sufficient oil pressure. If your bearings are still serviceable, you’re lucky. Most of the time, if your engine has to be torn down for an overhaul, it is also necessary to have the crankshaft turned at a machine shop and then install undersized rod bearings to fit it.
To get the rods and pistons out of the engine, you merely need to remove the connecting rod end caps and push the pistons through the top of the engine. Wrap the ends of the connecting rods with old socks or several layers of duct tape to keep them from scraping and scoring the cylinder bores when pushing them out through the bores. If the pistons hang up on a ridge at the top of the cylinders you will need to obtain a ridge cutter or reamer, available from an automotive tool store. Adjust the cutter so it will only cut a little at a time, then squirt light oil onto its blades. Now turn the cutter in each bore until the cylinder ridge is removed. Wipe up any residue or shavings with a rag.