Stock Cam Timing

[Morris]

Ugh... for some reason I am just not getting this. Geometry was the only class I made a C in in highschool. Maybe that has something to do with it.

Using my dial, I have found and marked TDC. I have also aligned the marks on my cam. But when I turn the crank, none of the readings I am taking from my degree wheel make sense to me.

According to Kent, my lobe centers should be 112. Does this mean that if I start at TDC before the intake stroke, my dial (which is following the intake lifter) should be at it's highest point at 112?

Is Hap telling met that if I advance that by a few degrees, I will get better performance?

 

[Hap Waldrop]

Is Hap telling met that if I advance that by a few degrees, I will get better performance?

Yes, that's exactly what I'm telling you, I advance every cam in every engine I build.

Ok, after TDC is determined and the degree wheel is adjusted to refelct TDC, and you need to be pretty darn close or everyhting else you will be off. Then with a dial indcator set up up on #2 pushrod with that lifter also in place, you rotate the engine to find the maxiumum lift, then zero out the dial indicator to reflect full lift. Pick a number, to stop at before top lift is reached on the dial indicator, I use .005, meaning I rotate the engine towards full lift I stop .005" before I reach full lift, record the reading on the degree wheel, say it's 89, then I go to full lift and still rotating the engine the lift will now start dropping I go back to the same .005" after full lift, ok say that number is 116, now add the two number together

89 + 116 = 205, 205 divided by 2 = 102.5, that's your cam timing.

Remember, to alway rotate the engine backwards by hand atleast .100" and then rotate clockwise to the full lift to get your numbers, what this does is take chain slop out of the equation.

I highly remcommend you buy Vizard's book if you don't already own it, it goes thru degreeing a cam as good as anything I ever read. If you own a Spridget, consider it an investment.

 

[Morris]

Thanks Hap. I have a Midget 1500, so I am not sure Vizards book will be such an investment for me.

That procedure makes sense. But I am still having a hard time figuring out what number my cam timing should be. Or rather, how I know when I have it in the right place.

Here are all the numbers I have:

Lobe centers 112°
Intake timeing 18°-58°
Seat duration 247°
.05" duration 205°

Which is the magic number that will tell me I have my cam set correctly?



Sorry I am so thick on this one.

 

[Hap Waldrop]

112 is the lobe center, lobe separation number, or center line or cam timing, all these terms mean the same thing.
Now what I would do is call APT and get as 4 degree offset keyway and advance that bad boy to 108. The keyway offset will go the counter clockwise side of the keyway slot for advancing the cam timing. You're right I didn't realize you had a 1500 engine, but all the above still applies as the second valve from the front of a 1500 is a intake valve and you always set up on the first intake valve to degree a cam.

 

[ChrisS]

Hap,
I'm a bit confused now. I thought lobe center / lobe separation meant the same thing and center line / cam timing meant the same thing, but not that they all were the same. Isn't lobe center / lobe separation dictated by the grind and therefor won't change if the cam is advanced?

Based on the numbers Morris gave this cam would be timed at 110' and would need a 2' offset key to be advanced to 108'. Please set me straight if I'm missing something.

By the way, what is the maximum offset key that you are confortable using?

 

[Morris]

For now I am happy to say that my cam is timed to stock specs. The timing marks on my car a bit errr... unclonclusive, but now I feel confident my timing is correct.

Thanks again ye automotive geniuses.

Ps. I will play around with advancing my cam once I have everything else running smoothly.