The article on this page has technical information and a step-by-step “ how-to ” procedure for engine removal and diagnostic disassembly for a 1960's era Chevrolet 235 CID 6 cylinder [ Stovebolt straight-six ] engine.
|Moonlight Engineering Automotive Service Company, Bakersfield, CA 93309-6385on|
Revised and updated article text by John Harlowe †
Both organizations still exist in the 21st Century and Jim Richardson continues to share his technical knowledge through various automotive publications and media.
Preface [ Removing the GM 235 CID Inline 6 Cylinder Engine ]
In its early days, the Chevrolet straight-six Stovebolt was always upstaged by the peppier, more glamorous Ford flathead V-8, even though the General Motors configuration of the straight six engine was a more dependable and less troublesome in terms of part failures.
Later, when the Chevrolet six was honed by years of development into the 235 CID of the mid-fifties, it was overshadowed by the company's own small block V-8, which is among the best American engines ever produced. The Chevrolet mid-1950 Stovebolt six cylinder engine is not as powerful as the V-8, but it is smoother, quieter, and more economical. Best of all, it is dead simple to work on.
Begin your engine removal by scribing around the hood hinges so you can reinstall the hood in the correct position. Remove the hood and set it aside where it won't get bumped or dented. Rest it on something soft and cover it with blankets. Next set the emergency brake, block the back wheels and put the front end of the car on sturdy jack stands. Never work under a car while it is on a jack. Doing so is extremely dangerous. A schoolmate of mine was killed when his car fell off a jack many years ago. When you are certain the car is properly supported, get under and drain the coolant, engine oil, and transmission fluid. I like those flat plastic containers with screw-on lids for this type of job. They are convenient and are available at most auto supply stores for a nominal price. Dispose of these fluids at a proper site such as your local service station.
Cover the fenders and grille of your car with old blankets or tarp's to protect them. Remove the battery, battery cables and support box to prevent accidents such as dropping tools across the poles of the battery. Label the wires then disconnect the wire harness that runs over the radiator support brace. Gently pull the harness out of the way. Remove the horns. The radiator hose and heater hoses should be taken off next. If the hoses are stuck after removing their clamps, try twisting them gently. If that doesn't achieve the desired result, slip a slot-head screwdriver under the stuck hose, shoot a little WD-40 into the gap and then gently twist the hose. Don't try this screwdriver maneuver on the radiator end of the hose because its inlets and tanks are made of soft brass, a slip of the screwdriver could cause damage. If you are unsuccessful after a determined effort to twist and pull the hoses off, cut them loose with a sharp utility knife.
If your car has an automatic transmission, disconnect, plug and remove the oil cooler lines. Tape cardboard over the radiator-core cooling fins to protect them. Remove the bolts holding the radiator support to the fender, side baffles, and cross-member, then lift the radiator out. Put it aside where it won't be damaged. Remove the fan, pulley, water pump, water inlet and thermostat. Save any gaskets, even if they are damaged, so they can be compared to the new ones for accuracy. Disconnect the wiring to the starter, generator, coil and temperature gauge sending unit as well as the ground wire from the engine to the chassis. At this point I also like to remove the starter, generator, distributor and vacuum advance tubing, fuel pump, fuel lines, breather pipe, dip stick, air filter, carburetor and throttle linkage so they won't get damaged in the process of lifting the engine from the chassis. Disconnect the exhaust pipe and remove the intake and exhaust manifolds.
Many people recommend the manifolds remain in place, but I believe it is safer to remove them with the engine in the car.
Finally, remove the windshield wiper motor to avoid bumping it with the engine and transmission as you remove them. Now get under the car and disconnect the linkage to the transmission and clutch and detach the speedometer cable. If your car is equipped with overdrive, disconnect the wiring and cables to the transmission. Take pictures, label the wires and make notes so you will know how to reattach these items. Split the rear universal joint by removing the four bolts that hold it together, put its bearing bolts back in their yokes and wire its bearing caps together to prevent the needle bearings from spilling out. Pull back on the drive shaft to slip it loose from the transmission. At this point the Chevy assembly manual recommends removing the engine and transmission together. But on cars equipped with standard transmission, I recommend renting a transmission jack and removing the transmission while the engine is still in the car.
After the engine is out you merely need to remove the bell housing in order to mount the engine on an engine stand.
Unbolt one of the upper transmission bolts and find two bolts with the same thread but a couple of inches longer. Cut the heads from these bolts with a hacksaw. Remove both upper transmission bolts and install your two headless bolts in their places These will serve as locator pins that will allow you to slide the transmission straight back to remove it so you won't damage the clutch or throw-out bearing. Screw your transmission jack up under the transmission, strap the transmission to it, then pull the transmission back and out. If your car has a Powerglide or Turboglide transmission, you will want to remove the transmission and engine as a unit as the manual recommends. A cherry picker hoist on casters with an arm that cantilevers over the engine compartment is best for engine removal. Never suspend a chain-fall from the rafters in your garage. Even a little Chevy six weighs more than 500 pounds and is capable of bringing the roof down on you.
Remove the valve cover, then loosen a couple of head bolts one at the right front side of the engine and one at the left rear. Attach the lifting chain to these bolts by slipping a link over each of the loosened bolt heads and then tightening the bolts back down. Allow at least 3 feet of 3/l6-inch chain with welded links for this purpose. If the chain is too short, the shallow angle could easily allow the chain to slide forward or backward through the hook of the cherry picker, causing the engine to shift uncontrollably. Also, a short chain will put excessive side loads on the head bolts. And although we're working with a six in this instance, I've found that the two-bolt method is secure enough to remove an engine as large as a Packard straight eight. When you are sure all the accessories are disconnected or out of the way, jack the hoist to take up the slack in the chain, then unbolt the motor mounts.
Be sure to have an assistant handy for this phase of the operation because you'll need help in guiding the engine as it comes out. Otherwise you could wind up slamming your motor into the sides of the car. Now jack the engine up and out of the car, and roll the hoist and engine out of the way, or roll the car out from under the hoist. The car will rise as you take the weight of the engine off the springs.
If your car came with a standard transmission, remove the bell housing and then attach the engine stand plate to the back of the engine and bolt it securely in place. If your car is Powerglide-equipped, detach the transmission from the engine being careful not to remove any of the torque converter cover bolts which extend through holes in the flywheel. You can place your engine and transmission carefully on your garage floor while you are working on this and use your hoist to lift and move the transmission when you have it separated from the engine. Now attach the engine to an engine stand.
On a 1957 Chevy, the rocker arms are numbered so it is easy to avoid scrambling them but earlier vehicles may not have the rocker arms numbered. If the rocker arms are not numbered by the factory, it would be wise to use a punch and stamp numbers into them, or, use a paint pen to mark the rocker arms. There are four different types of rocker arms on a Chevrolet straight six engine including left / right-hand intakes and left / right-hand exhaust rockers. Don't mix them up.
Disassemble the hairpin clips, springs, supports and rocker arms. As you disassemble the rocker arms from their shafts note whether their bearing surfaces are worn and whether their tips are worn where they ride on the push rods and valve stems. Also inspect the shafts to see if their oil galleries are clogged with dirt and whether they are worn where the rocker arms rotate on them. Replace any worn parts. Clean any sludge or varnish from inside the rocker arm shafts and the oil supply tube using a rifle bore cleaning tool and solvent. Summit Racing has these cleaning brushes for around $10 [ 05/07/2013 ]. It has been my experience that Summit Racing offers the lowest prices for stock and performance parts.
Next you will need to remove the push rods and valve lifters. But before you do, make a rack for them by drilling correct diameter holes in a piece of 1-by-2-inch wood to hold them in their proper order. It is important that lifters and push rods go back in their original places when they are reinstalled.
Pull the push rods out through the top of the head. Clean them with solvent and check to make sure they are straight by rolling them on a flat surface. Note whether their ends are worn. If any push rods are bent or worn, they should be replaced. Pull the lifters out of their holes. All of the 235-cubic-inch mid-195O Chevrolet inline-six engines were equipped with hydraulic lifters that gave excellent service, provided one followed a strict oil and filter change interval of 3000 miles or three months [ whichever comes first ]. If not, then dirty oil will cause premature lifter wear and that will result in lifter collapse. If your engine's lifters are old, worn or damaged, it's a good idea to replace them. Here are some things to look for. The plungers in the lifters must be free in the lifter bodies. To function properly, the plunger must drop of its own weight when the lifter is held vertically. Check lifters for free fit in the block, and make sure the ends that ride on the camshaft are not worn or pitted.
Worn lifters can be rebuilt, but they must be kept surgically clean during the process. The plungers are matched to their bores, so they are not interchangeable. If your old lifters are good, clean them thoroughly, then store them where they won't get dirty [ a coffee can with a lid works well ]. If the lifters are not in good condition, rebuild or replace them.
The next step in the engine rebuild process is to unbolt the head. The bolts are torque into place at 90 to 95 Lbs.-Ft., so you may need a breaker bar or extension to get them loose. If any seem to be stuck, tap on them rapidly with a ball peen hammer. Tapping a putty knife under the bolt head at several points is another way to pop it loose. If you break the heads off of any of the bolts, remove the rest of them, then use a stud remover to remove the broken ones.
After you have removed the head, inspect it for cracks around and between the valve seats. If you find any cracks, obtain another head. Fixes usually don't work well and heads for old Chevrolet straight-six engines are still available [ 05/07/2013 ] but one might need to do some Internet research to locate a good cylinder head at a reasonable price. Also observe whether there are any cracks in the block, especially between cylinder bores. A cracked block can be fixed but it is usually not worth the trouble on an engine as common as the Chevrolet inline six cylinder engine [ this engine is less common in 2013 then it was 18 years ago in 1995 ].
If you notice a heavy ridge at the tops of the cylinders, and its likely you will on a high mileage 235 CID straight-six engine, it probably means the engine will need to be re-bored. The ridge is formed because the piston rings does not ride up that far in the engine block so that area at the top of the cylinder bore does not experience wear.
Examine inside the water passages of the head and block. You may notice a rust buildup. If you do find rust use a screwdriver to dig the loose rust out of the head and block. Rust build-up will prevent the free flow of water around the pistons and valves and will cause your engine to overheat. Later your machinist will clean the head and block in the hot tank but it s a good idea to assist with this process by chipping away as much rust as possible.
At this point you may want to disassemble your valves and springs using a valve compressor tool or you may want to wait and let the machine shop take the head apart and tell you what you need. If you disassemble the valves and springs yourself store the little keepers that hold the valves in place in a plastic bag so you won't lose any of them. The valve springs will need to be tested for proper tension. Your machinist can usually do this for you. Your valve guides will also need to be checked by your machinist for wear.
In the next section the discussion continues with the disassembly of the bottom end of the six cylinder engine, an inspection the cylinder bores, crankshaft, bearings, wrist pins and camshaft for wear and what needs to be done to finish prep on the the engine for the machine shop. We will also talk about how to order the necessary parts to rebuild your engine.
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