installation d'un arbre à cames

By Steve Warner Photography : Steve Warner Brought to you by Sport Truck The key to making power is maximizing just the right combination of parts that, once installed, will make your entire powerplant come alive. Power starts at the camshaft--the heart of the engine. This is probably the single best area for realizing huge power gains because an aftermarket camshaft can increase valve lift and duration. Most truck manufacturers install an all-around camshaft, one that will keep the truck from suffering poor gas mileage and will make decent power in all situations whether it's cruising, towing, or racing. You can, however, change the camshaft in your engine and then specifically tailor the new camshaft to your exact needs. For example, if you plan to use the truck most often for towing heavy loads, then use a camshaft specifically designed to produce more torque in the low rpm range. All of the big manufacturers offer a technical hotline to address your needs. For our application, we wanted the maximum horsepower we could achieve without having to increase the stock compression ratio or go to more exotic pistons and crankshaft. So we consulted the folks at the Crane technical support hotline. They advised us to use one of their Compucam hydraulic roller camshafts. The following information about how to install the Compucam camshaft applies to any and all hydraulic and roller tappet camshafts. So, if you want to maximize your engine's performance without adding more expensive power bolt-ons like superchargers and turbochargers, a camshaft, lifter, valve spring, and rocker arm swap may be just what the doctor ordered. Article Source: Crane Cams

With the use of a Crane Compucam hydraulic roller camshaft, this bone-stock small-block Chevy realized a 15hp and 15 lb-ft of torque increase at 5,000 rpm. The entire building process should take no more than one full weekend if the engine remains in the truck, or about 3-4 hours if you remove it to perform the work.

Crane offers its Compucam camshaft in various sizes and configurations. Besides a hydraulic roller camshaft, it’s also available as a straight hydraulic piece. The camshaft profile card that’s included in every camshaft box states that this Compucam is a dual pattern camshaft that offers both mid and upper rpm horsepower gains in all vehicles equipped with 3.45:1 or lower rearend gears. Also included is a complete set of hydraulic roller lifters. Crane recommends changing the stock valve springs to new ones with a higher spring rate. Your stock production valve springs should work fine provided they aren’t intended for any horsepower extremes. If they are, then matched components such as the camshaft, lifters and valve springs never hurt. Crane also recommends replacing the stock rocker arms with more valve-timed-accurate roller rocker arms.

Judging from Crane Cams-generated horsepower and torque figures, the Compucam we installed into our engine made some very decent power gains across the entire engine’s operating band. As advertised, the Compucam made the most horsepower and torque at the mid to upper rpm range. All in all, we’d say the additional power was well worth the effort.

We are not going cover the entire disassembly process that has to occur prior to installing the Crane Compucam camshaft. The provided instruction manual does a very good job describing exactly what needs to be removed if the engine remains in the truck or if it is being built outside of the truck. Even though this is a hydraulic roller camshaft, the following steps are the same for a standard hydraulic tappet camshaft. Once the factory camshaft has been removed (be careful to not damage the cam bearings in the engine block), coat the new Crane Compucam camshaft with the break-in lubricant. Some mechanics say that you can coat the new camshaft in motor oil, Crane recommends, however, its camshaft break-in assembly lube for the fire-up stage. Coating the camshaft prevents premature metal wear upon initial fire-up.

Carefully install the Compucam into the opening. Once you get the camshaft past each cam bearing in the engine block the camshaft will want to drop free on its lobes. DO NOT let this happen. You can seriously damage the camshaft lobes and possibly break free the camshaft bearings. Our new Crane Compucam offers an advertised duration of 264 degrees on the intake side and 270 degress on the exhaust. It’s set on a 112-degree lobe centerline. Duration at 0.050 inch is 208 degrees on the intake side and 214 degrees on the exhaust. The 0.050 figure is the one more commonly recognized by camshaft manufacturers, engine builders and performance people in the know, because it’s a more accurate figure than the advertised duration figure. This particular camshaft is designed to operate most effectively between 1,600 and 5,200 rpm.

All small-block roller camshafted engines include a cam walk-out plate that must be removed then reinstalled after the new camshaft has been installed. The cam walk-out plate helps to keep the camshaft properly positioned in the engine under normal and extreme high-rpm operation. If you don’t plan to chang the camshaft in the near future, coat the cam walk-out bolts with Loctite thread-locking compound to ensure they don’t come lose.

Normally, most camshaft manufacturer’s recommend replacing the factory timing chain with a new, more efficient double roller chain. Because this engine has but 10,000 miles on it and we plan to do more camshaft swaps, we elected to use the original factory timing chain. We did, however, check the chain to make sure the OEM timing chain hadn’t stretched beyond service limits during those 10,000 miles.

We elected to install our Compucam camshaft straight up. What this means is that the camshaft is neither retarded nor advanced. To install it straight up, simply rotate the new camshaft until the dot on the upper timing gear is inline with the dot on the lower crankshaft gear. Many premium engine builders will tell you that you should always degree the new camshaft with a degree wheel. Normally, when valve tolerances and extremely high horsepower gains are the goal, we would agree. We have also, however, degreed more than a good amount of camshafts and found most to be off by no more than a degree or two. Most of the major camshaft manufacturers make their camshafts’ timing so exact that when it’s off by a degree or two, you will never know the difference, nor will you feel a 1-2hp gain or loss when driving.

The timing chain cover can now be reinstalled. If you didn’t remove the engine from the truck, reinstalling the timing chain cover can be a real chore. Because of the oil pan’s upper lip, getting the timing chain cover to properly seat without having to pull out the alignment dowel pins in the engine block is a hassle. There are two solutions, one extremely hard and messy, the other very quick and painless. You can completely remove all of the oil pan bolts and, prior to installation of the timing chain cover, drop the front of the pan, then once the cover is on, reinstall the oil pan. Or you can do as we did. Take a pair of tin snips and carefully trim off the two corners of the timing chain cover lip. This way the cover will slip over the upper lip of the oil pan very easily and still maintain its correct seal once everything is put back together.

Next, reinstall the harmonic balancer. Slip it over the crankshaft snout and push it back on until it bottoms out. You will only be able to push it on so far by hand. So go get a relatively inexpensive crankshaft installation tool from your local auto parts store. It will make the job a lot easier (don’t hammer on the old harmonic balancer with a sledge hammer and a 2x4-inch piece of wood as we have seen so often before).

The roller lifters simply drop into the valley of the engine block. Because these are roller lifters, they include an aluminum retainer that helps keep them in place. If this were a standard hydraulic lifter, you would prelubricate the lifter and lifter bore prior to installation. Simply drop the roller lifter into there. Once it rests atop the camshaft lobe, move on to the next one, and so forth until all 16 lifters are in place.

We followed Crane’s recommendation to change our valve springs. The easiest way to do this is go to your auto parts store and purchase a spark plug adapter air hose designed to hold the intake and exhaust valves closed using compressed air. Screw the adapter into the spark plug hose and supply it with air. This should hold the valve closed and allow you to change each valve spring.

Using a valve spring compressor, carefully pull down on it until you can remove the valve spring keepers. We elected to use a small magnetized screw starter so we wouldn’t drop the keepers into the lifter valley.

If you release the compressed air, the valve will drop down, so it’s better to work on changing one valve spring at a time. With the valve spring keepers removed, pull off the old valve spring and install the new one as we have done. This particular set of Crane valve springs are double-wound and complement the matching Compucam camshaft and roller lifters.

The remaining step is to install the new Crane roller rail rocker arms. We offer this comparison of what roller rail rocker arms are versus nonroller rail rocker arms. Basically, the only difference between a rail rocker and a non-rail rocker is the small rail on the end of the roller tip of the arm (arrows). With the use of a rail rocker arm you eliminate the need for a pushrod guideplate. On older small-block cylinder heads there is a small hole that the pushrod fits through. This is essentially a poor man’s guideplate. With newer cylinder heads and bigger pushrods, that small hole has been eliminated and is now a groove, hence the need for a guideplate to control the pushrod to keep the valve spring and rocker arms from becoming loose and wobbly. You can also use roller rail rocker arms on older nonrail rocker arms if you simply remove the stock pushrod guideplate.

Install the new Crane roller rail rocker arms. Prior to firing up the engine, you will need to make the proper valve adjustments. Adjust the rocker arm nut until there is zero lash with the exhaust valve fully closed. To do so, tighten the rocker arm nut and with the other hand slowly spin the pushrod with your thumb and forefinger. Once the pushrod no longer moves freely, tighten the hex-head nut another half to full turn and tighten the set screw. Then rotate the engine until the intake valve has fully opened and repeat the zero lash procedure, as shown above, on the exhaust valve. Once the engine is ready to fire up, check for any oil leaks and listen for any possible squeaks or squeals which may be caused by something binding up or improperly installed.

Homepage          Retour Techniques et Divers         Haut de page       Milieu de page