Rebuilding a Chevy Straight Six – Part 5

Rebuilding a Chevy “Stovebolt” Six Part 5

Section 5: (Reassembly, part 2)

In the last installment of our engine rebuild series, we cleaned the block and bearing saddles and reassembled the bottom end, which included the installation of the cam and crankshaft, pistons and connecting rods. This month we will finish building what is commonly referred to as the short block, or the engine minus its accessories.

Before we start on the top of the engine, we need to install the oil pump and its basket, then attach the pan. Rotate the engine on an engine stand so it is at about a 45 degree angle with the top of the engine upwards and the crankshaft portion down. Now fill the oil pump with fresh 10-30 oil, rotate its gears, and refill it. Slip the pump into place in the block and tighten its attaching lock screw. Make sure the tapered end of the lock screw goes down into the hole in the oil pump body, and then tighten the lock nut securely.

It is necessary to fill the oil pump so the engine will develop oil pressure quickly on its initial startup. If you don’t fill it, there is a risk that your engine won’t develop oil pressure in the first critical seconds of its running life. This could result in scored cylinder walls, burned bearings and even a ruined engine.

Install the oil lines and filter basket assembly. Make sure the lines to the oil pump are properly installed to eliminate the possibility of pump shaft seizure when the lines are tightened in place. Another note of caution: If the mesh in your pickup basket is torn or damaged, replace it or find another basket. On many vintage engines oil cleansing is minimal. As time goes by, if you should neglect to change your engine’s oil, torn mesh in your oil pump pickup basket could allow larger particles of contamination to enter oil galleries, block them and starve the rod and main bearings for lubrication.

Once the oil pump assembly is in place, it is time to install the pan. Lay the gasket on the pan to make certain it fits correctly. Sometimes gaskets have two distinct sides with one meant for the pan and the other for the block. Smear the pan’s mating surface and the mating side of its cork gasket with a thin coat of silicone sealer. Let the sealer get tacky. Now gently press the gasket into place on the pan and position it carefully. Do not coat the bottom of the block or the top of the pan gasket with sealer. It is not necessary to prevent leakage, and besides, you may need to remove the pan at a later date.

Gently place the pan on the engine block and hold it in position while you loosely install two or three of its bolts. Install the rest of the bolts loosely. Snug them up evenly in a couple of stages, working from the center of the pan out to its corners. Check your manual for proper bolt torque figures and don’t over-tighten. If you tighten the pan bolts too much, the cork gaskets used on many engines will be excessively compressed and therefore ruined.

Timing Gear Cover and Harmonic Balancer

Before you attach the timing gear cover, make sure the cover has a new seal where the harmonic balancer goes through it to the crankshaft. Coat the cover’s mating surface, both sides of its gasket, and the mating surface of the block with silicone sealer and allow the sealer to become tacky. Now slip a centering tool, (Chevy made a special tool for this purpose, but good luck finding one) made from a piece of correct-diameter tubing, over the end of the crankshaft, then slide the timing gear cover into place over the tool. Don’t attempt to install the timing gear cover without some kind of centering tool, because its seal must fit evenly against the harmonic balancer to prevent oil leaks. Install the cover screws loosely, then tighten them evenly in a couple of stages to between 6½ and 7 lb.-ft. of torque. Again, don’t over-tighten because you may develop oil leaks from a deformed gear cover if you do.

The harmonic balancer goes on next. Smear a little grease on the seal. Now line up the harmonic balancer on the keyway of the crankshaft. Use a hammer and drift, a round soft metal tool, to tap the balancer evenly into place until it bottoms against the crankshaft gear behind it.

Head and Rocker Arm Assemblies

On engines with overhead valves, the machine shop usually seats the valves and installs new valve guides, valves and springs. Before mounting the head on the block, however, it’s a good idea to check the shoulder heights of the valve guides. If the valve guides are too low in the head, valves can stick. If hey are too high, the valves may lot seat correctly. Check the shoulder heights of the valve guides by lacing a steel machinist’s straight edge next to the valve springs. Check your shop manual for the correct height for your engine.

Inspect the valve keepers to make sure the machine shop used new ones when installing the valves. In overhead valve engines this is critical, because if a valve keeper breaks, your engine may swallow a valve while it is running. This will give it a terminal case of indigestion and possibly ruin your block.

Now turn the engine upright in the engine stand. Inspect the deck mating surface on the block for the head, and make certain the piston tops and bores are completely clean. Although we cleaned these areas in our last installment and covered the engine with a plastic tarp when we weren’t working on it (January ’96), if any particles of debris are found, wipe down the areas with soft cloth and some lacquer thinner or WD-40. Even a little grit or dirt can wreak havoc with a new engine. Place the head gasket on the engine and make sure it has all the required holes and they line up correctly with those on the block.

Fashion a couple of guide pins to help install your engine’s head. Pick up a couple of extra long bolts at the hardware store that have the same threads as your head bolts and cut their heads off. Using your fingers only, tighten them into head bolt holes on either end of the block so they can act as locator pins for your head and head gasket. Before going on to the next assembly steps, put an old set of spark plugs in your engine’s head to help keep out dirt. (Use old plugs because they may be bumped and damaged during the assembly process.)

Coat the head gasket on both sides with a good sealer such as Gaskacinch; make sure you have the gasket perfectly aligned so all the bolt holes and water passages are open, then gently press the gasket into place on the block. Set the head on next. If the head on your engine is a long, heavy, cast iron type like the one on our Stove Bolt six, get a friend to help you lower it on so you won’t accidentally dent or deform the gasket. Coat the head bolt threads with a little Permatex or silicone sealer, tighten the head bolts into place with your fingers, then remove the guide pins and install the last two bolts.

Using a torque wrench, tighten down all the head bolts evenly in three stages to the correct specification following the bolt-tightening sequence shown in your shop manual. If you don’t have a tightening sequence diagram to follow for your engine, start at the center of the head and work out toward either end of it, alternating back and forth as you go. The head bolt torque specification for our little Chevy six is 90 to 95 lb.-ft. of torque, but other engine’s specs may differ.

Lifters, Pushrods, Rocker Arms

Make sure hydraulic lifters are filled with oil, coat the lifters lightly with oil, and then drop them into their holes. If you are reinstalling your old lifters, put them into the same holes they came from, as they will mate best with their original pushrods. Now oil the ends and set the pushrods into place above the lifters. If you are using your original pushrods, put them back where they came from as well.

The rocker arm assemblies go on next. In a previous installment of our engine rebuilding series (October ’95), we discussed cleaning, reassembly, and making sure they are kept in sequence. On a Chevy six, as on many older engines, there are four types of rocker arms. (They include separate right and left exhaust and intake configurations.) To assure proper alignment to the valve stems, the rocker arms must be arranged in their correct order. Make sure the pushrods are seated in the rocker arms, then tighten the rocker arm assemblies evenly into place using a torque wrench. A common torque rating for these bolts is 25 to 30 lb.-ft.

The technique and specifications for preliminary valve adjustments vary depending on year and make as well as whether an engine has hydraulic or mechanical lifters. The job usually involves bringing each cylinder up to TDC (Top Dead Center) then adjusting the gaps between the ends of the rocker arms and the ends of the valve stems to the specifications stated in your shop manual.

Coat one side of the valve cover gasket and the mating surface on the valve cover with silicone sealer allow them become tacky and press the gasket into place. Set the valve cover on the head and install its bolts. Snug them evenly in two stages, but again, don’t over-tighten. Attach the engine side plate using the same technique. In both cases, only use sealant on one side of the gasket so you can remove these panels later. The oil pressure in these areas of the engine is minimal, so you won’t have leaks, even without sealer on both mating surfaces, providing the gaskets are evenly tightened into place.

Attaching Manifolds

In the case of our Chevy six, the intake and exhaust manifolds are attached, as was common practice on inline engines of the past. Such integrated manifolds should be taken, still lofted together, to the machine shop so their mating surfaces can be planed flat. Long manifolds on inline engines are prone to warping. If they are not planed during an overhaul, they may crack from stress when tightened back onto the cylinder head. To reinstall manifolds on an inline engine, attach them loosely, then – with the manifold pilot sleeves and gaskets in place – attach them loosely to the head. Tighten everything evenly in three stages working from the center of the manifolds out to the ends. Check your shop manual for the proper torque. On our Chevy, the center clamp bolts require 15 to 20 lb.-ft. of torque, while the two end clamp bolts require 25 to 30 lb.-ft. of torque.

In the next issue of CLASSIC AUTO RESTORER we’ll complete our assembly procedures, attach the bell housing and flywheel, and reinstall our engine. There will also be tips on starting your engine for the first time.

By | 2018-07-22T02:08:22-06:00 May 3rd, 2018|Classic Chevy Trucks|0 Comments

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