Engine Build Pre-Assembly (Cam Degreeing)

 

The next step in my build is to degree the camshaft.  Some people may say "why not just slap it in there, it's a brand new Comp Cam".  Well, I could do that.  Chances of something being wrong with it are probably pretty small, BUT... I wasn't there when they machined it, packaged it and sent it.  So I want to verify that the cam that came to me is in fact the right one I ordered.  To verify this I have to "degree the camshaft".  Every new cam comes with a cam card that lists all the specific data about when the cam will be opening and closing the intake and exhaust valves, I will be making sure I can get these same numbers.


Below is the cam card that came with my camshaft.  I will be verifying the duration @.050" lift numbers, lobe lift, intake and exhaust centerlines and lobe separation for both the intake and exhaust cam lobes  

 

 

 

These are the tools I will be needing to degree the cam.  A dial indicator and magnetic base, a crankshaft degree wheel, crankshaft turning socket, and a wire pointer attached to the block (I used a wire coat hanger).

 

 

 

First thing to do is to find true TDC (Top dead center) of the #1 piston.  This is the exact point where the piston is at it's highest point in the cylinder.  This needs to be absolutely correct because it is the reference point that all the cam card data is based on.  I know this because during my first attempt at degreeing the cam I must have somehow knocked the degree wheel making TDC incorrect.   I was getting totally wrong numbers and scratching my head.  Finally I started over and found TDC again, after that the numbers were all correct.

 

I rotated the engine over clockwise until I got it as close to TDC by eye.  I then lined the pointer on the degree wheel up to 0(TDC).

 

I then set the dial indicator up on the top of the piston and zeroed the dial. 

The engine was turned counterclockwise until the piston was 0.100" BTDC(Before Top Dead Center).  I then rotated it back clockwise until the dial read 0.050" BTDC( I rotated it back to 0.100" BTDC and then back up to 0.050" to take the slack out of the timing chain).  With the piston at 0.050" BTDC the degree reading was taken from the wheel.

 

 

 

 

 

The engine was then turned clockwise again until the piston was reading 0.050" ATDC (After Top Dead Center).  The reading on the degree wheel was taken again.

 

TDC is the midpoint between the two numbers, so the engine is turned to that midpoint between the results.  Without moving the crank the degree wheel is then rotated so the pointer is then at "0".  The process was then repeated until the number BTDC and ATDC were the same.  At that point the "0" on the wheel should be exact TDC.

2 Lifters were then oiled and put into the lifter bores.

Making sure the lifters were both in the lowest points (valves would be closed). I set the dial indicator up on the intake lifter with a 5" pointer extension on the dial as can be seen in the picture below.  From this point on I didn't seem to take very good pictures of what I was doing.  So basically I followed the camshaft degreeing procedure included with my cam.  I will try and explain what I did.

I rotated the engine clockwise until maximum lift was achieved (dial indicator reverses direction at max lift).  The dial was zeroed at this point.  The engine was then rotated counterclockwise to 0.100" on the dial (taking slack out of timing chain), and then rotated back clockwise to 0.050" before max lift.  The reading on the degree wheel was recorded.   The engine was then rotated again past the max lift (zero on dial now) to the 0.050" mark on the closing side.  The reading on the degree wheel was recorded again.  The two numbers are added together and divided by 2.  This is the intake centerline result.  In my case was 106 degrees

To find the intake duration.  Making sure the intake lifter is on the base circle of the cam lobe (closed) the dial was zeroed.  The engine was rotated until the intake opened to 0.050".  The reading was taken off of the degree wheel.  The engine was rotated again until max lobe lift was achieved, This was also recorded.  The engine was then rotated again until 0.050" before closing ("0" on dial).  The reading was taken again off the degree wheel.  To calculate the "Intake duration @ 0.050" lift" is the first reading plus the second reading plus 180.  In my case I came up with 242.5 degrees, which is off by 0.5 degrees and close enough in my opinion.  The intake lobe lift I measured was bang on at 0.319".

To measure the exhaust lobe numbers I moved the dial indicator setup over to the exhaust lifter and repeated the same procedure.  The exhaust centerline I measured was 113 degrees.  The "exhaust duration @ 0.050" lift" was 248 degrees.  The exhaust lobe lift I measured was 0.330".

To calculate the lobe separation is calculated by adding the two centerlines together and dividing by 2.  So in my case 106+113/2= 109.5. 

It took me a few times to get the hang of this procedure, but after doing it the second time I am happy with the numbers I got and they matched the cam card numbers within 0.5 a degree.  I think I am going to go through it one more time before I finish assembling the engine just to be sure.