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> How To Degree A Cam In An LS Engine - Step By Step
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post Feb 2 2011, 09:35 PM
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From the March, 2011 issue of Car Craft
By Jeff Smith
Photography by Jeff Smith

Horsepower has never been easier to make, and the motor leading the charge is the new LS engine. What we've learned is that just the simple addition of a more aggressive camshaft can easily add 50 to 100 hp to an otherwise stock LS engine. This applies to virtually all the LS series of engines. And if you're going to the effort of bolting in a camshaft, you might as well degree it to ensure it will be timed properly. If you've never degreed a camshaft, now is a great time to learn. And if you've been through it a few times before, much of this will be very familiar, even if we're doing it on a new engine. Let's get started.



With a few simple tools and a little bit of camshaft knowledge, you can degree a camshaft in a matter of minutes.




Details There are some interesting details about cam timing that may come in handy when you begin the engine-building process. The lobe-separation angle (sometimes called the lobe-center angle) is the distance in cam degrees between the intake and exhaust lobe centerlines. Decreasing the angle (106 versus 114 degrees) between these lobe centerlines increases the amount of overlap. Generally, with longer-duration camshafts, a wider lobe-separation angle is needed to maintain a given amount of overlap. If duration is increased and lobe-separation angle is tightened, it drastically increases the amount of overlap. Conversely, a wide lobe-separation angle used in stock LS engines can approach 116 to 118 degrees or more, reduce the overlap, and create a very smooth idle.

As an example, the cam we used in the degree process has a lobe-separation angle of 113 degrees, yet the intake centerline is listed as 109 degrees ATDC. If a camshaft is ground with no advance, the intake centerline and lobe-separation angle will be the same. With the Comp cam used in our story, the intake centerline is actually 4 degrees advanced in relation to TDC. Most cam manufacturers dial a certain amount of advance into cams intended for street use to improve low-speed throttle response with earlier opening and closing points. Since the camshaft is already advanced before it finds its way into the engine, degreeing the cam is important to verify the valve opening and closing points and also points out why advancing the cam further may not be a good idea.

The intake centerline method is also not the only way to degree your camshaft. Among the intake and exhaust valve opening and closing points, intake closing is by far the most important. Advancing or retarding the camshaft is really all about positioning the intake closing point. Since most cam cards list intake and exhaust opening and closing points at 0.050-inch tappet lift, a quick check would be to compare the cam's intake closing point at 0.050 with the data on the cam card. If the numbers agree, the cam is installed properly, or you can use the referenced intake closing point to either advance or retard the cam.



To simplify this story, we've already installed the Comp roller cam and a new timing set, in this case with the multikey crank key installed 2 degrees advanced as a starting point.



Comp Cams offers a new LS engine-specific degree kit designed for use with the cylinder heads off. An option for the standard LS kit is this larger 16-inch degree wheel. The standard LS kit comes with a 9-inch wheel and trick aluminum adapters to securely mount the dial indicator on the engine. We've also included separate part numbers in case all you need is one of the components in this kit.



The first step is to mount the degree wheel on the crankshaft. The crankshaft socket fits over the oil pump drive lug splines and uses a special brass-tipped Allen screw to secure the adapter to the crank snout. Now position the 16-inch degree wheel on the crankshaft socket and secure it with the large knurled nut.



Using a length of copper wire supplied in the kit, we attached the coiled end to the engine and bent it at a 90-degree angle to serve as a pointer. Make sure to align the wire with the degree marks. This will make reading the degree wheel easier.



Using the 1/2-inch drive ratchet feature on the end of the crank socket, turn the engine clockwise until the No. 1 piston (driver side front) is at the top of its travel. Loosen the large knurled knob of the crank socket and position the degree wheel to align top dead center (TDC) with the pointer.



Now turn the engine counterclockwise about 30 degrees and mount the piston stop over the No. 1 piston. LS engines use a very unusual 11 mm x 2.0 head bolt that is impossible to find in common bolt outlets. Neither Rutland nor Grainger carry this oddball die to make threads. We cut down a pair of stock head bolts to secure the piston stop to the block.



This is the most important step in the entire degreeing process. You must accurately determine TDC or all other measurements will be inaccurate. With the piston stop securely in place, carefully turn the engine clockwise until the piston contacts the stop. Record the degree wheel reading-in our case, it was 35 degrees before top dead center (BTDC). Now turn the engine counterclockwise until the piston again hits the stop. The degree wheel will be at true TDC when both piston stop numbers are the same. Let's say the numbers do not agree with 36 on one side and 40 on the other. Halfway would be 38 degrees, so move the wheel to that number and double-check your results.



With TDC now set, we can move on to determining the camshaft's position relative to TDC. This simple illustration reveals the relationship of the intake lobe centerline to TDC. This particular camshaft uses an intake centerline of 109 degrees, which is the number of crankshaft degrees after top dead center (ATDC). This illustration makes it easy to see that if the cam measures 113 degrees ATDC, then the intake lobe is opening and closing later (retarded). Conversely, if the intake centerline is at 104 degrees ATDC, it is opening and closing earlier, which means the cam is advanced relative to TDC.



Armed with this knowledge, we can now measure the actual cam position in the engine. We attached the very cool aluminum dial indicator fixture to the small threaded hole in the block for the plastic lifter holder. Position the dial indicator using the 5-inch extension to align the plunger with the edge of the lifter.



Place the dial indicator plunger extension on the edge of the lifter body as shown. Do not use the pushrod cup because its radius will cause erratic readings. Rotate the engine through several revolutions to ensure that the dial indicator is positioned properly so it reads maximum lift and always returns to zero.



Comp Cams recommends checking cam position using the intake centerline method, which is pretty simple. First rotate the engine until the dial indicator reaches maximum lift and then zero the indicator. Turn the engine counterclockwise until the indicator reads 60 to 70 degrees on the opening side of the lobe. Now rotate the engine clockwise until the indicator reads 0.050 inch before max lift.



With the indicator on 0.050 before max lift, read the degree wheel, which in our case is 65 degrees ATDC. Record this number.



Next, rotate the engine clockwise past max lift until the indicator reads 0.050 inch on the closing side of the lobe and record the number on the degree wheel. In our case, the second reading produced 149 degrees ATDC. Using these two numbers, we can find the true position of the intake centerline.



All we have to do to determine intake centerline is add the two numbers together and divide by 2. So adding 65 + 149 = 214/2 = 107 degrees ATDC for the intake centerline. Looking back at installing the crankshaft sprocket, we advanced the cam 2 degrees, which is what we now have. So by resetting the crank sprocket at 0 (retarding the cam 2 degrees), the intake centerline will be a true 109 degrees ATDC.



This is the digital version of a Comp cam card. The card supplied with the camshaft also includes intake and exhaust opening and closing points at 0.050-inch tappet lift.



PARTS LIST
DESCRIPTION-PN-SOURCE-PRICE

Comp Cams LS cam degree kit-4942-Summit Racing-$187.95
Comp LS timing set-7106-Summit Racing-$126.95
Comp Cams camshaft-54-469-11-Summit Racing-$396.95
Comp 16-inch degree wheel-4791-Summit Racing-$187.95
Comp 9-inch degree wheel-4790-Summit Racing-$16.95
Comp LS crankshaft socket-4914-Summit Racing-$47.95
Comp head-off TDC stop, universal-4933-Summit Racing-$10.95
Comp 0-1-inch dial indicator-4909-Summit Racing-$31.95
Comp heads-off degree fixture-4901-Summit Racing-$75.95
Comp 5-inch indicator extension- 4912-Summit Racing-$9.25
ARP cam bolts-134-1003-Summit Racing-$6.15


Here endith the lesson


--------------------

Motor & Transmission By John Kuiper Race Engines.
Suspension & Brakes By Ron Missian Motor Sports.
To See My Build Album Click On Any Of The Below Pics.

Priscilla, Queen Of The Vettes
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