Few things excite us more...
Few things excite us more than new parts right out of the package. They glisten and pump us up to start building the engine. But make no mistake, defective parts are made and shipped every day. Degreeing a camshaft is important because it confirms camshaft and crankshaft integrity.
You lean on the throttle and your classic Ford runs like it's chained to a tree. Maybe it's overheating or the exhaust headers glow red-hot under a light load. Performance and reliability begin with proper cam timing during an engine build or cam swap. It's crucial to performance and engine life as well.
We take so much for granted when we plan and build engines. We install new parts right out of the box under the assumption they are ready for installation. Did you know, however, that each and every new part should be thoroughly inspected before installation? Trust the manufacturer-but verify quality control. Assuming you have a good part can become time consuming and expensive if you don't inspect it before installation.
Take, for example, camshaft/valvetrain parts and installation. If you believe degreeing a cam is unnecessary and a waste of time, consider this: The single greatest cause of engine failure across the board is camshaft and valvetrain malfunction. Improper valve timing and irregular cam-lobe indexing can cause engine failure in a nanosecond. Failure typically occurs at high rpm when an engine is most vulnerable, when you're on the throttle and need power most.
How to Check Cam Timing
Why should you check a camshaft for proper timing? Degreeing a camshaft is what separates engine builders from engine assemblers. Engine assemblers gather parts and screw them together. Engine builders are architects and engineers who know what to expect at the end result. They want absolute assurance that all parts will work together in perfect harmony. This mandates fierce discipline and close attention to detail in every phase of engine planning and execution.
When you buy parts, there's no guarantee they'll be safe. Even the most reputable manufacturers in the industry experience failure issues from time to time, in everything from Main Street to NASCAR and NHRA competition. As long as human beings make the parts-or program the computers that make the parts-there will be failure. Inspection, your last line of defense, is what saves you the expense and inconvenience of engine failure.
Degreeing a camshaft helps to confirm valve-timing events as they relate to piston travel and crankshaft rotation. Although most cam manufacturers have a good track record when it comes to cam-card accuracy, there's always a chance you might wind up with a mispackaged camshaft or a defective cam out of index that doesn't match specifications. It's always better to discover a defective or mispackaged camshaft during installation than to wonder why performance isn't as expected once an engine is buttoned up. Camshaft flaws don't have to be huge to adversely affect performance. Lobes that are off one or two degrees will alter performance significantly and can lead to serious engine damage.
You have to think of your engine not as a V-8 or a six-cylinder, but as eight or six individual single-cylinder engines sharing a common crankshaft. Each bore has endless variables-compression, airflow, chamber size, piston-to-cylinder-wall clearances, ring dynamics, piston weight, deck height, cylinder finish-that make it different from the rest. Each cylinder is as unique as a human fingerprint.
A camshaft consists of egg-shaped lobes and journals on a common shaft. These elements are positioned on a core machined to specifications. Each cam lobe has a base circle and lobe. A pushrod V-8 has 16 of them, sixes have 12. Lobes open valves and springs close them. Each lobe consists of two clearance ramps, a nose, and two flanks. When valves are closed, lifters (also known as tappets) sit on a base circle 180 degrees opposite the nose. Flanks control the speed at which valves open. Clearance ramps take up valve lash. Lifters ride cam lobes to convert rotary camshaft motion (roundy-round) into linear (back and forth) motion.
Get all of your cam-degreeing...
Get all of your cam-degreeing equipment from Comp Cams. Complete kits are affordable and easy to use.
Valve timing is related in the number of degrees of crankshaft rotation (not camshaft rotation) as before top dead center (BTDC), after top dead center (ATDC), or top dead center (TDC). When the piston is at its highest point in travel, it's at TDC. At its lowest, it's at bottom dead center (BDC). Cam specs also include before bottom dead center (BBDC) and after bottom dead center (ABDC). Expect to see these terms on your manufacturer's cam card.
The amount of time expressed in crankshaft rotation is the number of degrees between valve unseat (opening) and valve seat (closed) and is called duration. Cam manufacturers have two ways of expressing this specification-duration and advertised duration. Advertised duration is almost always different than actual duration. Cam-shaft manufacturers tend to show both duration and duration at 0.050 inch in these specifications. It has been said that Harvey Crane of Crane Cams started a camshaft revolution by establishing the industry-standard duration of 0.050 inch.
Duration at 0.050 inch refers to the number of degrees of crankshaft rotation from 0.050 inch of lifter rise until the lifter reaches 0.050 inch of rise before the valve closes completely. True duration is from valve unseat to valve seat. Cam cards typically have both specifications. Some manufacturers base their numbers on duration at 0.006 inch or duration at 0.002 inch, so be fully prepared for any possibility. It's a shell game based on the desire to look better-on paper-than the competition.
In reality, duration is as unique as the cam grinder's specifications. Any way you slice or dice duration, it's the length of time in crankshaft degrees that the valves are off their seats.
The first step in cam degreeing...
The first step in cam degreeing is determining top dead center (TDC). True TDC is when the piston travels as far as possible during that brief crank rollover upstroke. At TDC, there is piston dwell time of 1-2 degrees, depending on rod ratio. The same is true at bottom dead center (BDC). Here, we check TDC with a dial-indicator-the most accurate way to determine true TDC.
This is another type of TDC...
This is another type of TDC indicator, one with a mechanical stop. It's not as accurate as a dial indicator, but it's effective. Move the piston to TDC; then adjust the stop to touch the piston crown. Gently roll the crank back and forth and feel the TDC 1- to 2-degree dwell. You want the crank dead center in the middle of TDC, which will feel like a loose spot in rotation before the piston moves into the downstroke. Find the middle of the loose spot in crank rotation, which is dwell time and true TDC.
Cam degreeing isn't just to...
Cam degreeing isn't just to determine camshaft integrity; it's also intended to examine crank index accuracy. Not all crankshafts are spot on. Some cranks are off due to manufacturing irregularities or abuse. Determine journal accuracy with a degree wheel and TDC indicator.
Although timing sets are marked...
Although timing sets are marked with timing marks, this doesn't mean cam timing is accurate. Cam degreeing determines the accuracy of both these marks along with cam lobe indexing.
To set up a degree wheel,...
To set up a degree wheel, begin with the TDC indicator to determine true TDC. This will be "0" on the degree wheel. You also need a pointer, positioned just about anywhere on the front of the block near the degree wheel. Here's the 180-degree position, or 1/2 turn of crankshaft rotation. This timing pointer is at 163 degrees.
Crankshaft degrees are directly...
Crankshaft degrees are directly proportional to piston position. For example, when the No. 1 piston is at TDC, so is the No. 6 piston. You can degree both at the same time. Although most engine builders degree cams on the No. 1 cylinder only, we suggest degreeing all eight cylinders for added assurance. The best approach is to follow firing order. Document information from all eight bores and compare findings. This provides the most accurate cam-timing information possible.
A dial indicator is placed...
A dial indicator is placed on the intake lifter first, then exhaust. Slowly turn the crank, watch lifter movement, and record the findings. See how your findings compare with the cam card.
Because we're dealing with four-cycle engines, the crankshaft turns 720 degrees for every power cycle-two complete 360-degree revolutions. Each valve opens once in those 720 degrees of rotation. Power and performance are determined by when we open each valve, how much, how aggressively, and for how long.
Duration gives us a beginning and end to valve action, but what about events in between? Study a cam lobe and you'll see the dynamics of valve action. Flat-tappet cam lobes look different than roller-tappet lobes, and roller smoothness enables us to open and close valves more aggressively. We can also open valves further without the shortcomings of a high-lift, long-duration, flat-tappet cam.
Flat tappets don't ride squarely on cam lobes. They ride to one side in order to achieve rotation and smoother operation. To make this happen, flat tappets are spherical-rising 0.002 inch toward their centers. They have to spin in their bores to prevent excessive friction and wear. Roller tappets ride dead center on cam lobes, thanks to roller technology and smoothness. This greatly reduces frictional power losses. What's more, roller cams virtually never wear out.
At one time, cam lobes took on all kinds of bizarre shapes and paths to achieve given results. This was known as triple-curve or harmonic shape and applied more to flathead designs. Overhead-valve technology, which became more common in the '40s and '50s, changed all the rules. Detroit had to approach cam design differently with the advent of overhead-valve engines.
To degree a cam, you need the following:
- Degree wheel
- Dial indicator
- TDC indicator
- 1/2-inch drive, 1 5/16-inch socket, and breaker bar
The degree wheel, which attaches to the crankshaft, tells you in degrees where the crankshaft is positioned relative to its 360-degree journey. Zero degrees is TDC. It's also 360 degrees when we make one full revolution of the crankshaft. All we have to do is establish TDC on the No. 1 cylinder. It doesn't have to be that cylinder, however; it can be any one you choose. Just make sure you're on the compression stroke at TDC for that particular bore when setting the degree wheel at zero.
Once you have TDC dialed in, don't disturb the degree-wheel position on the crank, as that will change TDC accuracy and throw off everything, forcing you to start over.
This entire setup includes...
This entire setup includes a degree wheel from Comp Cams and the dial indicator. The dial indicator measures lobe lift off of the base circle. When we read the degree wheel, we get duration. It's a good idea to measure duration two ways-off the base circle and from 0.050 inch to 0.050 inch. To ensure accuracy, check lift and duration twice on each cylinder and record your findings with each.
After establishing zero degrees at TDC, roll the crank one full turn (360 degrees), and make sure the degree wheel is properly positioned. Now you're ready for cam timing.
Locate the manufacturer's cam-specification card. The cam card will tell you exact valve opening and closing specifications (duration). To confirm accuracy, you need a dial indicator with a measuring range of at least 1 inch on each lifter. With both valves closed, set the dial indicator at zero. Begin with the intake valve; slowly turn the crank clockwise until the lifter rises 0.050 inch. Stop turning the crank and read the degree wheel. This begins duration at 0.050 inch. If our cam card says the intake valve opens at 31 degrees BTDC, the degree wheel should show 31 degrees BTDC at this time.
On a cylinder-by-cylinder basis, record your reading. Slowly rotate the crankshaft clockwise and watch the lifter rise to the top of the lobe and then record lift. Continue turning the crankshaft and stop when the lifter reaches 0.050 inch above zero (base circle). Our cam card says intake closes at 67 degrees ABDC; we should see 67 degrees on the degree wheel. Repeat this procedure on all eight intake lobes.
Once you've checked and recorded all intake lobes, look over your findings with the cam card. Don't be surprised to find readings that are off 2-4 degrees from cam-card figures. Sometimes it's the camshaft and sometimes it's your crankshaft keyway. The crankshaft keyway should be in perfect alignment with sprocket timing marks at 12 and 6 o'clock. You have options that will get your timing spot on. We'll get into those shortly.
Repeat the same procedure on each of the exhaust valve lifters and record your findings. See how they compare with the manufacturer's cam card. Again, slowly turn the crank with each lobe and carefully document your findings. Every lobe should yield the same findings.
Advancing valve timing raises cylinder pressure because both valves close earlier. This should improve low and midrange torque. Retarding cam timing improves high-rpm performance, sacrificing low-end torque. For street performance, it's a good idea-depending on the camshaft-to advance timing 2-4 degrees. This should improve overall performance. Pay close attention to piston-to-valve clearances whenever you're advancing or retarding cam timing. This is a lot of work, but so is building another engine because you didn't catch all the details.
A Homemade Degree Wheel Forty...
A Homemade Degree Wheel
Forty years ago, Marvin McAfee of MCE Engines in Los Angeles fabricated his own billet-aluminum degree wheel because no one offered anything like it in the marketplace. He takes it further with not only degrees, but fractions of a degree for extreme accuracy. As McAfee dials in a camshaft, he makes notations on the degree wheel with a felt-tip marker. After recording his findings, he removes the markings with lacquer thinner and a rag. Note the custom fabricated pointer, too.
When advancing or retarding...
When advancing or retarding cam timing, always check piston-to-valve clearances with a head temporarily bolted into place. Mold modeling clay into the valve reliefs and observe valve impressions. Minimum valve-to-piston clearance is 0.060 inch. Ideally, you will have more.
Here, we have advanced cam...
Here, we have advanced cam timing at the crank by 2 degrees (2A). Rotating the crank gear to the proper advance (A) or retard (R) timing marks is an easy way to achieve the needed timing correction.
Another way to advance or...
Another way to advance or retard cam timing is at the cam itself. Drill out the pin hole per the manufacturer's directions and use the appropriate offset eccentric. Kits typically include five eccentrics-five different advance and retard positions.
Another option is an offset...
Another option is an offset crankshaft key, available in various advance or retard positions, which enables you to advance or retard the crank sprocket.
One method of advancing or...
One method of advancing or retarding valve timing is a double-roller timing-chain set with an adjustable crank sprocket. Advance or retard valve timing as much as 8 degrees by moving the sprocket clockwise or counterclockwise around the crank Woodruff key. This mandates extreme caution. Check valve-to-piston clearances. We advance or retard cam timing to modify where we want power to happen. However, sometimes cam indexing from the manufacturer is off enough to warrant advance or retard depending on valve timing events.
Here's a good example of valve...
Here's a good example of valve overlap on a degree wheel. Note the exhaust valve open and close time as it segues to intake valve open. This is called valve overlap, where we take advantage of intake velocity and exhaust scavenging. This helps cylinder pressure at high revs.
Crank degrees also show up...
Crank degrees also show up on the harmonic balancer. This is total ignition timing at 3,000 rpm-in this case, 34-36 degrees BTDC.
Another important issue when...
Another important issue when addressing camshaft lobe lift is rocker-arm ratio. When it's 1.6:1, there's 1.6 times the lift than at the cam lobe. There's lobe lift and there's valve lift. Based on rocker-arm ratio, there's always more lift at the valve than at the lobe.