Читать книгу Chevrolet Inline-6 Engine 1929-1962 - Deve Krehbiel - Страница 13

CHAPTER 3

THE HEAD AND ASSOCIATED PARTS

The lifters on this specific engine are hydraulic. Hydraulic lifters get their name by filling with engine oil on engine startup and then compressing/decompressing as they move up and down over the camshaft. This makes for a much quieter and smooth-running engine. A retainer clip on the top of a hydraulic lifter holds in the internal parts.

Solid lifters are as named: solid. They have a cone on the top to accept the pushrod but no internal parts, thus no retaining clip.

You can learn if your engine has solid or hydraulic lifters by shining a flashlight down the pushrod hole. If there is a retaining clip on the top of the lifter, they are hydraulic.

This is not needed if you did your homework on the identification because the block’s numbers tell you which type you have. Cars usually had hydraulics and trucks always had solids.

The head assembly after cleaning the rockers. Once cleaned, it’s important to refit to make sure you have all rockers and shims in the exact spot they were in before disassembly. Spray all that pretty, clean metal with WD-40 for safe keeping.

Lifters

Load each lifter one at a time into the small parts cleaner, making sure to keep the parts together and not mix them with any of the others. My first three didn’t have retainer clips, so I substituted a 3/4-inch snap-ring retainer from one of my boxes. The edge of the retainer may need to be carefully ground down, so it is away from the pushrod, but it’s a very solid fix.

These hydraulic lifters may have been the originals; you can see the wear patterns. With a thorough cleaning, they could be reused without problems.

The cleaning product Simple Green can be your friend in the shop. This stuff even cuts through the pitch left on saw blades when woodworking. It works great for removing residual kerosene.

Once the parts are cleaned using kerosene and a soft brush, soak them overnight in Simple Green cleanser. This removes all the petroleum-based contaminants so you start off with fresh metal. Use a soft, green Scotch-Brite pad for cleaning, rinsing each part carefully and applying some engine oil to all the surfaces.

Lifter Reassembly

With oil all over everything, including inside the lifter housing, turn the inner lifter barrel upside down and place the ball bearing over the hole, then place the ball bearing cover over the top of it. I like to drip a little oil over this assembly to sort of make everything stick together.

Next, place the tension spring on top of the ball bearing cover. Everything should go together perfectly. If it doesn’t, you are doing something wrong.

Now, while balancing the inner housing, ball bearing, ball bearing cap, and tension spring in one hand, turn the lifter housing upside down and gently twist it down over the assembly. It should be smooth until you feel some hydraulic resistance. Most of the resistance is from air being trapped between the two barrels. With a very small, thin tool (I used the plastic straw from a WD-40 can), push on the ball bearing just a little until you feel the resistance burp away.

From left to right: tension spring, ball bearing cover, pushrod cap, inner lifter barrel, ball bearing, and lifter housing. Not shown is the 3/4-inch snap-ring retainer. After a thorough cleaning, the parts look practically new.

Keeping a little downward pressure on the assembly, place it on a flat surface and fill the inner lifter barrel to the top with engine oil. Place the pushrod cap over the top. This cap pushes down below the surface of the lifter housing. Place the snap ring in the pliers and hold it over the pushrod cap, push down on the assembly using a pushrod so that the cap is sufficiently below the surface of the lifter housing to get the snap ring to engage. (Keep in mind that most lifters have their own retaining spring that is much easier to install, but I am telling you this just in case you run into what I did.)

You should have one fully loaded, fully burped, serviceable hydraulic lifter. Now do that 11 more times. When finished, find a nice container that you can use to hold all 12 of them and be able to fill it with engine oil over the top of the lifters.

These lifters are fully assembled and ready for reinstallation, it’s a good idea to soak the parts in oil for safe keeping. This keeps them filled with oil, which is a good way to start the first engine runup.

For this build, the machine shop decided that it would cost the same amount to purchase new hydraulic lifters as it would cost to resurface the old ones ($7.50 each). With that in mind, I just had the shop order new ones. The effort was not wasted, I learned something new!

Pushrods

You need to test the pushrods (mine were also in the box) to be sure they are perfectly straight and that each end is in the proper condition to be used. To do this, you find a perfectly flat surface (glass is good) and roll them across your work table or bench, watching for any wandering or out-of-straight condition. If they are not straight, do not try to bend them back; just get new ones.

The machine shop advised that these be replaced due to very small pits in the metal. These rods get a lot of abuse and the worry of failure is too likely.

Next, carefully inspect each end to make sure the little hole in the center is pronounced and clean. If there is any residue in the center, clean it thoroughly so that its surface is shiny and smooth. You can go the extra mile and clean the entire length with Scotch-Brite or similar pads. Test for straightness one last time.

In this rebuild, I was not happy with the condition of five of the pushrods. One had a very significant wear spot that reduced the diameter and the others were slightly bent. Luckily, I had a box of old pushrods from other Stovebolts and found five perfect replacements. This engine has 11¼-inch pushrods.

Even after all that, the machine shop wasn’t comfortable with some of the pitting, so new rods were obtained for this engine. This is why you should box up everything and take it to the machine shop for a proper inspection. My collection of pushrods is getting bigger!

The 1954–1962 235/261 engines used 11¼ × 5/16-inch pushrods. Never try to straighten a bent rod. The metal has memory, and it won’t be long before it fails again. New ones cost about $7, and it is cheap insurance to replace those that are pitted, bent, or cracked.

The lifter end of the pushrod is shiny due to its metal-to-metal contact. The hole in the center is to allow for a small amount of oil.

The design of the rocker end of the pushrod captures the rocker assembly so everything stays straight and true. The indention allows for a small amount of oil.

Rocker Assembly

The rocker assembly is bolted on top of the head and consists of two shafts, the rockers, the springs, etc. This is the assembly for adjusting your valves. It goes together in only one correct way. Getting any shim or spring in the wrong place leads to excessive wear or premature failure. This assembly is notorious for being dirty, mostly or completely clogged, and the mounts can be stuck to the rocker shaft.

If everything looks in order after a cursory cleaning, it’s time to get your hands dirty. You can never have enough pictures of this assembly because every shim, every washer, every spring, and every rocker needs to be assembled in the exact order it was taken apart.

If the parts are simply sitting in a box, reconstruct the assembly to make sure that you have all the parts and everything is serviceable. Once complete, take a picture, so you have a template on how to put it back together. You can also refer to the photo in the shop manual.

This engine is the newer-style 235 with a center-flow spout that has no second tube coming out and looping back to the bottom of the assembly. This newer style puts all the upper engine oil flow through the rocker assembly shaft system before dumping it back into the reservoir.

Cleaning

Here too, you need to clean things thoroughly before even thinking about a successful assembly. Too often, cleaning reveals something you need to address. In this case, I go out of my way to ensure that this assembly is perfectly clean. To do this, you really want to take it apart carefully and place components in the proper order. In this example, two rocker shafts meet in the middle. Once disassembled, these two shafts need to be inspected carefully for excessive wear. It’s very common for these rocker shafts to be considerably worn where the rockers move on them. It’s worse when there is no oil reaching the rockers. In this engine, both shafts have very little wear and look really good for their age.

Take about a 14-inch piece of 3/8-inch steel rod and push it all the way through the inside of the shaft. Do it very slowly and knock off all the crud with a small screwdriver (or similar) as you go past each hole. Use your parts washer’s pump action to push kerosene through the shaft. Repeat this until the kerosene comes out clean.

This style of rocker assembly (the newer style) has no oil-return pipe. All of the oil going to the upper end goes through the rocker shaft assembly before being dumped back out into the reservoir.

On the outside, use double-O steel wool to make sure the entire surface is perfectly smooth. Don’t expect to remove all the stains, but do clean it thoroughly. Don’t use an aggressive grinding wire wheel for this. You need to keep as much of the finish as possible. Do not sandblast the shaft.

You need to clean all the rocker assembly parts. First run them through the kerosene wash, use a wire brush, dry them off, then remove the pushrod contact assembly from the rocker arms. You want to thoroughly inspect the ball that comes in contact with the pushrods to ensure that there is no damage or excessive wear. You also do not want to damage that part of the rocker. Once apart, clean the rockers including the valve contact area with kerosene and light oil.

This super cleaning was accomplished by taping all machined surfaces with masking tape then bead blasting the outside of each rocker. Don’t forget to chase all the passages and clean thoroughly after blasting.

You want to clean each rocker thoroughly. Chase the threads, use a piece of safety wire or a paper clip to clean the oil hole. Once blasted, run some 400-grit sandpaper through the shaft hole, on the flats of everything. When assembling, remember that the shaft’s oil holes face downward. Once the entire assembly has been cleaned, put it back on the head to make sure each rocker contacts the valves exactly in the middle. Once you are happy with the cleaning job, spray some WD-40 all over the assembly to keep the rust at bay during the rest of the project. Set the assembly aside.

I like to leave about three threads showing on the rockers. This is a good neutral position for the valve adjustment procedure later. As this rebuild progresses, you will be glad you addressed these issues before going to the engine machine shop. Had any lifters or rods been damaged or you want a second opinion, you will have this information beforehand.

Head Machining Prep

You will save money and time at the machine shop if you remove the valves beforehand. One threaded plug needs to be removed and saved for later, and to make life easier for the machine shop, also take out the valves. You must do this at least once to appreciate how badly these valves can become abused.

To remove the valves, you need a valve spring compressor similar to the one in the tools list. You may prefer a throat about an inch longer.

The rocker assembly is now ready for the finished head. Spray the outside of any super clean assembly with WD-40 to keep things from rusting.

With everything cleaned and working like new, you can set the whole assembly aside awaiting the finished head. Notice how the WD-40 brings out the shininess and makes it look normal again.

Be careful with the spring compressor. Lock the handle, then turn the crank handle, making sure you are solidly on the valve on one end and centered on the spring on the other. Once you turn the screw sufficiently, the keepers either fall out or can be retrieved with a small screwdriver. Break the plastic retainer and then let pressure off the spring the same way. The spring should safely come out, and the valve should slip out as well. If it doesn’t, I use the handle end of my hammer to tap it a little.

This is where you need to get to before you send the head to the machine shop. Everything must be removed. You will not be reusing the valves, and if the springs do not meet specs (as ascertained by the machine shop), they will be replaced too.

Be sure to remove all plugs and fittings. Take it easy on the temperature sensor on top of the head. That fitting is very difficult to find. It is not a standard NPT size on pre-1955 vehicles.

Once compressed, the keepers almost fall out. Carefully remove the keepers, then do it 11 more times.

Place the valve spring compressor carefully in the center of the valve shaft. It is not as dangerous as with the suspension of a car, but always think safety first when removing springs under load.

Damage from a poor-running engine looks like this. This engine is in need of a valve job. It never ceases to amaze me how these engines run anyway, despite the damage to a point.

All of this crud was attached to the valve. Something went terribly wrong. Discoloration of the metal proves that something was causing them to become abnormally hot.

Be sure to remove any fittings on the head. When the engine shop cleans the head, the techs can do a better job with everything removed. If you cannot remove a fitting, let the shop know.

Remove the temperature sensor carefully. This one is easy, but the ones used for vehicles prior to 1955 have a nonstandard thread size and need to be taken out with care. Any copper line to this sensor needs to be handled carefully because it contains a special gas and cannot be opened or crimped.