Cam Degree Question

[Kozlow]

HI,

I am trying to degree my camshaft, but I have a problem.

Cam lobe separation = 110 degrees
The cam has 4 degrees of advance ground into it.
I have the timing chain gears at 0, no advance or retard.
I want to install cam center line at 106 degrees.

If I check the cam center line .050 down from high point of intake cam lobe on either side, add the two locations together, divide by 2, it checks right on at 106 degrees.

But...

Then when I check the opening and closing location @.015 as per cam card, the cam checks 2 degrees retarded. Which puts center line @ 108 degrees.

So,

Is it better to run as is,
or
Advance the cam 2 degrees?

If I advance 2 degrees, and check .050 down from the high point the cam, center line would be @104 degrees. But the opening and closing locations would be correct to cam card and center line would be at 106 there.
It seems like the opening and closing would be more important.

What you think?
Steve

 

[PurpleBeeper]

Holy crap... that simple math hurts your head doesn't it? Maybe call the cam manufacturer and ask for their recommendation?

 

[BSB67]

I think the 0.015" is a bit too close to the base as very slight errors can show up as a few degrees.

Try 0.050" from the bottom, and another at some random mid point. This is mostly to verify if the results are similar between the three and makes sense. Then you'll need to decide which number to follow, as today's asymmetrical lobes will have a changing CL by a couple of degrees as you move the measuring point around.

 

[Kozlow]

Holy crap... that simple math hurts your head doesn't it? Maybe call the cam manufacturer and ask for their recommendation?

Yes that's probably sound advice.
They recommended to make the opening and closing points right.


Steve

 

[Kozlow]

I think the 0.015" is a bit too close to the base as very slight errors can show up as a few degrees.

Try 0.050" from the bottom, and another at some random mid point. This is mostly to verify if the results are similar between the three and makes sense. Then you'll need to decide which number to follow, as today's asymmetrical lobes will have a changing CL by a couple of degrees as you move the measuring point around.

So with the timing gear advanced 2 degrees I get...

@.015 - 106 center line and opening and closing degrees matching cam card,
@.050 - 105.5°
@.150 - 104.75°
@.200 - 104.5°
@ + and - .05 from lobe center - 104.25°

Yeah, I guess if the lobe profile was asymmetrical it would produce a false center line when calculating.
So the opening and closing points would seem to be a more accurate way to set it up.

Steve

 

[PRHeads]

You’re good where it is with that last set of numbers.

I’ve checked several cams where there was almost a 2* difference in theoretical c/l between the .050 from closed readings and the .050 from peak readings.

 

[Kozlow]

You’re good where it is with that last set of numbers.

I’ve checked several cams where there was almost a 2* difference in theoretical c/l between the .050 from closed readings and the .050 from peak readings.

Thanks for your input, I feel a little better.

I was figuring that it would be better to be a little advanced then retarded, because the chain must stretch a little as it breaks in and retard the timing some.
Not sure how much, but it must change some.

Besides, nobody wants to be a little retarded! Lol

 

[mopar 3 B]

The four degrees built in should take care of chain stretch later.

 

[dvw]

I agree the opening closing points are more important than the actual intake C/L.
Doug