|
|
A Matter Of Timing
How To Swap A Hydraulic Roller Cam In A Late-Model Small-Block
February, 2009
By Jeff Smith
Photography by Jeff Smith
 |  We chose a Crane CompuCam...  We chose a Crane CompuCam 2031 hydraulic roller cam to replace the stock cam in our 305. The cam is equipped with an iron distributor drive gear to make it compatible with a stock iron distributor gear. We reused stock lifters on the cam matched with a set of Crane guided 1.6:1 narrow-body roller rocker arms. We also added a set of matched Crane valvesprings in order to control the valve motion of our new cam. Not appearing in the photo is a new Crane multi-keyed timing chain and gear. This timing set allows you to easily move the camshaft relative to top dead center (TDC). Its always a good idea to install a new timing set when swapping cams to ensure accurate cam timing. |  With any roller-tappet cam,...  With any roller-tappet cam, a fixture must be employed to prevent the lifter from turning sideways in its bore and damaging the cam and lifter. Chevys approach to this is to use a stamped tin spider retainer that bolts to bosses in the lifter valley. |  When bolted in place, as shown...  When bolted in place, as shown above, the spider places a load on eight horizontal tie bars that slip over the lifter. This arrangement works well at low engine speeds. However, if the engine enters valve float due to over-revving, its possible for the spider to bend, allowing the tie bars to pop off the lifters. The lifters are then free to spin in the bore, which will instantly destroy them along with the camshaft. This is an excellent reason not to over-rev factory hydraulic roller cam motors. |  To get to the cam drive, the...  To get to the cam drive, the first step is to use a dedicated puller to remove the harmonic damper. We used a screwdriver to prevent turning the engine over as we removed the damper. Next remove the timing chain cover bolts. Before you can remove the timing chain cover, you will need to loosen all the oil pan bolts and remove most of the front bolts to allow room to drop the front part of the pan down to clear the timing chain cover. As an aside, if the engine is equipped with a four-piece gasket, this is a great time to remove the pan altogether and replace it. Fel-Pro makes an excellent one-piece pan gasket that will replace the four-piece item, making reinstallation a breeze. |  Next remove the old timing...  Next remove the old timing chain and gear. You will also need a puller to remove the original crank gear. As the photo shows, the new crank gear will have three or more slots to line up with the crankshaft keyway. One slot will be for straight up, or no advance; one will offer 4 degrees of advance (slot A); and one will offer 4 degrees of timing retard (slot R). These are offered to allow you to custom-set the valve opening and closing points relative to TDC. The small eccentric cam bushings can also be used if you prefer. These bushings, available from Crane, Moroso, Mr. Gasket, and others, are often set in 1- or 2-degree increments. This does require that you drill a 0.400-inch hole in the cam gear to accommodate the larger bushing. The trick is to drill this hole from the back but not to drill all the way through. This retains the eccentric in the gear. |  Before you install the new...  Before you install the new roller cam, be sure to completely clean all machine surfaces. Crane ships its cams with a protective coating that must be removed before the cam is installed in the engine. Also do not coat the cam lobes with the heavy, moly-style cam lube used with flat-tappet camshafts. This heavy lube will clog the area around the roller bearings and prevent oil from lubricating them, causing early failure. Apply engine oil to the cam lobes and roller tappets with a small amount of moly lube on the distributor gear only. |  Note the difference in the...  Note the difference in the new style cam gear drive face on the camshaft in the block (right) compared to the standard flat-face camshaft (left). This different face on the cam indicates this is a hydraulic roller camshaft that also uses a cam retention thrust plate over the front of the cam. The two bolt holes on either side of the cam are used to fasten this thrust plate to the block. While difficult to see in the photo, there are also 0.030-inch holes drilled in the two outboard oil galley plugs (arrows) used to lubricate the cam gear and chain. |  Install the new timing chain...  Install the new timing chain and gear. The new crank gear can be installed using a length of thick-wall steel pipe with a cap welded on the other end to use as a driver. Or, if you dont have anything like this, you can carefully drive the gear on the crankshaft using a brass (not steel) drift punch. Weve also used a small piece of wood when no other tools were available. Line up the cam gear mark with the appropriate mark on the crank gear. Start by installing the crank gear in the straight up or zero advance position. Most cams check within one degree of where they are supposed to be installed. |  For most street engines, its...  For most street engines, its not necessary to degree the camshaft in the engine. This is mainly a blueprinting step that ensures the cam is installed exactly where the engine builder desires. For this installation, we did go through the motions by using Cranes degree wheel. If you have access to one of these trick dial indicator tools (available through Crane), it makes degreeing the cam much simpler. Note that the tool has two different cam follower faces, one for flat-tappet and one for roller-tappet cams. This tool will only work with the heads removed. |  We degreed the cam using a...  We degreed the cam using a typical dial indicator mounted off the pushrod. Since this engine had aluminum heads, there was no convenient place to put the magnetic base for the dial indicator. We fabricated a right-angle mounting plate out of 3/16-inch steel and bolted it to the front of the head to be able to check valve motion on cylinder No. 1. Remember that the second lifter in front is the No. 1 intake valve lifter. The first tappet in the front of the block on the driver side is the No. 1 exhaust. Make sure the dial indicator is lined up directly with the pushrod. This will eliminate reading errors. |  We wont go through each...  We wont go through each step to degree the cam, since this has been covered many times in the past (see A Matter of Degrees, Sept. 98). Cranes specs call for the No. 1 intake to open at 3 degrees before TDC. This is indicated on the timing card as (3) ATD, which can be confusing. The parentheses indicate that the timing figure is actually a negative number, which means that -3 degrees after Top Dead Center (ATDC) is actually 3 degrees before Top Dead Center. Yeah, we know, its confusingespecially since this represents a difference of 6 degrees between 3 degrees ATDC and 3 degrees BTDC! We discovered our cam was installed straight up at TDC, or 3 degrees retarded. We chose to advance the cam 4 degrees, ultimately placing it at 1 degree advanced compared to Cranes specs. |  With the cam degreed, we moved...  With the cam degreed, we moved to the cylinder heads, where we used an air pressure adapter from a compression tester to put air into each cylinder so we could change valvesprings. We used a Crane flat bar tool to remove the springs and a small magnet to retrieve the keepers. |  We used Cranes 1.6:1...  We used Cranes 1.6:1 guided roller rockers (right) to replace the guided stamped rocker arms (second from right). The standard Crane roller rocker is at far left, with the standard style stamped rocker second from left. The guided rockers use rails to straddle the valve stem tip in order to center the rocker over the valve stem. This eliminates the need for a pushrod guideplate. Never use guided rockers with a pushrod guideplate. These Crane rockers are also a narrow body design to clear most centerbolt valve covers, but we still needed to grind clearance on the magnesium Corvette-style valve covers for the rocker arms. |  We installed new Crane matching...  We installed new Crane matching valvesprings after checking the installed height to ensure that there would be no coil bind or retainer-to-seal clearance problems. Basically, if the valvetrain generates 0.450 inch of total valve lift, then the installed height should accommodate at least 0.500 inch of total lift before coil bind. There should also be at least a 0.050-inch clearance between the bottom of the retainer and the top of the seal at max valve lift. This will prevent seal damage. Note the use of positive valve seals on this engine. |  The final step is to set the...  The final step is to set the lifters. The easiest way to accomplish this is to treat each cylinder individually. Turn the engine over clockwise (from the front) and watch each rocker arm. When the exhaust valve just begins to open, you can adjust the intake rocker until all the clearance is eliminated. Then turn the adjuster an additional half turn. Once that is set, turn the engine over again until the intake rocker arm is almost closed. Then set the exhaust rocker just like you did with the intake, removing all clearance and then adding a half turn of preload. This is best done before you install the intake manifold since it makes it easy to look at the lifter and see when all clearance is removed. Now button up the rest of the engine and youre ready to check out your new camshaft. |
Camshaft swaps are one of those essential conversions that, sooner or later, every hot rodder will perform. Typically, these stories have always dealt with flat-tappet camshafts, so we thought it would be a change of pace to swap a cam in a late-model hydraulic roller cam motor. These engines are a little easier to work on than the older small-blocks yet also require a couple of extra steps to complete the job. We chose to work on an 88 305 with aluminum Corvette heads, but the details around the cam swap will apply to any roller cam small-block Chevy. Plus, while we wont get into the details in this story, it is possible to install a hydraulic roller cam into a preroller cam small-block Chevy with excellent results. The main difference is that factory hydraulic roller lifters cannot be used because there is no provision in the early blocks for the roller lifter spider that retains the stock lifters. For these engines, you must use aftermarket hydraulic roller tappets. The cam we chose for this engine is a Crane CompuCam grind that offers a little more lift and duration (see the Cam Specs sidebar) while still retaining excellent street manners. We also included new valvesprings to handle the extra lift from both the cam and a set of 1.6:1 Crane guided roller rockers. Since we were replacing the stock hydraulic roller cam, we reused the original roller tappets. You can also purchase new factory-style hydraulic roller lifters from Crane if your high-mileage tappets are suspect. Always inspect used lifters to ensure they are in good condition before putting them back in service. In order to squeeze the major points of the swap into a few short pages, we performed the swap on an engine out of the vehicle. Weve also already pulled the intake manifold to reveal the lifter valley. Of course you will need to first drain the coolant before pulling the intake manifold and replace the intake gasket when reassembling the engine after the new cam is installed. Now that weve set the stage, lets get to the meat of the swap.
Chevrolet Corvette Research
Find new Chevrolet Corvette information as well as review photos, specs and more. The Corvette has a V8 standard engine producing 505 horsepower, and has a 8 star frontal impact rating for the driver and a 8 star frontal impact rating for the passenger. You may also be interested in the Chevrolet Impala and the Chevrolet Camaro.
|
|
|
Size Matters
You know the deal about bigger carburetion being better and more fuel equaling more power......
more
|
|
|
Somewhere In Time
The SS 396 Chevelle put the musclecar movement into Fourth gear in 1966. The middleweight Chevrolet...
more
|
|
|
Timing Is Everything
There’s a proper time for everything. Driving through an intersection just a little too soon...
more
|
|
|
Closing Time
Although the basic purpose of a valvespring is to close the valve while also ensuring that the...
more
|
|
|
|
|
|
|
|
|
|
|
|
TV Time
Most people think they spend too much time with the TV, but when it comes to Bow-Tie hot rodders,...
more
|
|
|
|
|
|
|
|