Degreeing the cam

[AngleT]

I have a PBS S-2 cam that I'm trying to degree. This is my first time doing this and have some questions. First, here is the link for the cam data
http://pbseng.com/Camdata.html
From what I've read, the cam should be degreed at .050" of lift. When the dial indicator rises (or in our case drops) to .050", look at your degree wheel (that TDC has been verified) and look at what it is reading. Then go through the valve stroke and when it drops to that same .050" reading on the dial indicator, take another reading from the degree wheel.
This seems fairly simple, but the references on the cam data spread sheet have me confused. Should I be looking at lobe center with reference to the degree wheel on the crank? Or should I be looking at the duration of lift @ .050"? The duration number seems a little large considering there are only 360 degrees in a circle.

Just trying to get the reference numbers stright before I set the dial indicator up.

Thanks for the help.

 

[AngeloX19]

Your .050 to .050 reading will give you total duration, the half way point is your lobe center. Set that in reference to the crank, ie whe the crank has rotated 112 degrees ATDC. Remember too that the crank rotates twice for every cam rotation.

The way I used to set up a cam was find my peak lift, decide what lobe center I wanted to use, if one wasn't supplied and rotate the cam back that number of degrees to give me TDC. Because the cam spins 1/2 of crank, 112 degrees crank meant I would rotate back the cam 56 degrees if my wheel was set on the cam pulley. Mark the cambox, and then bring the pistons up to TDC on build and I was done.

Hope this helps.

 

[AngleT]

brain fart

There are two rotations to the crank for every 1 rotation of the cam. This equals 720 degrees of crank rotation.

It made a little more since after I watched this video on YouTube
(This video turned out to be very wrong. Do not believe everything you see on YouTube!)
[ame="http://www.youtube.com/watch?v=la6-EgnCOl4"]YouTube - CRANKSHAFT CAMSHAFT TIMING DEGREE WHEEL INSTRUCTIONS ON DVD[/ame]

(This math is wrong too)
As I understand it now...
1. Take reading of degree wheel on crank at BTDC and ATDC @ .050" of cam lift on the dial indicator.
2. Add the two numbers together
3. Divide by 2 to find the center of cam lobe in degrees on crank
4. Compare to Lobe Center (S-2 cam = 112) on data sheet
5. Make adjustments by advancing or retarding the cam as necessary to achieve specified lobe center measurement.

If this sounds questionable, let me know.

Thanks,

 

[AngleT]

Thanks

I think we were posting at the same time.

 

[AngleT]

YouTube can't be trusted

That guy must not have known what he was doing either. Here is why.
Lobe center will never change.
Let's use his numbers 76 BTDC and 140 ATDC
76 + 140 = 216/2 = 108
Let's advance the cam. So, the intake valve will open sooner... it will also close later.
60 + 156 = 216/2 = 108
If the intake opens sooner (advance the cam), it closes later. If it opens later (retard the cam) it closes sooner. The math he gives doesn't change where the lobe center is. It will always be at 108 degrees.

I realized his info was wrong when I found it ironic that my eyeballed cam timing happen to be dead on when I set up my dial indicator. To check, I advanced the cam 1 tooth and got the same answer to his math problem.
The question is where to put the lobe center. I called PBS to see if they could point me in the right direction.
The S-2 cam has the same lobe profile for the intake and exhaust, so this process will work for this cam but may not work for other cams. There is a point that both the intake and exhaust valves are open at the same time. This is called scavenging and is a good thing. When the crank is at TDC the intake valve should be opening .071" and the exhaust should be .071" away from closing. As long at the readings at TDC are the same for the intake and exhaust, your good to go.
It turned out that I was about 1/2 tooth off with my "eyeball" method. Today I will put everything back together and see how it runs. I will post pics and video of the results this evening.