964 Cam Timing in 3.0L: Timing Specs & Method Check
 

A couple of questions regarding 964 cam timing on my 3.0L rebuild:

1. I have a 3.0L with 8.8:1 compression, 50mm intake valves, 964 cams, and will be running CIS. I know the base 964 intake overlap setting is 1.26mm, but what is the acceptable range or variance for this setting? Also is there a particular setting that would work better with setup? Most of the driving will be street/highway/canyons in that order.

2. I have been trying to set my cam timing at 1.26mm (.050") and I am very close but cannot get it right on the money. I dont know if there is some chain/sprocket backlash that is throwing me off or if I am making a mistake, or both.

Lash is set on both intake and exhaust rockers on #1 and #4. I have Stomski-style solid tensioners in place (SR011). Using #4 as an example, during my initial setting, once I rotate the crank clockwise to read .050" of lift, if my pulley notch is a bit off, I pull the pin, rotate counterclockwise maybe 1/4 turn past TDC, then clockwise slowly sneak up on Z1. Once on the notch I double check that my dial measurement has not moved, then I set the pin and washer and bolt. At this point the pulley is at Z1 and the dial still measures .050". Theoretically perfect.

Then I rotate the crank clockwise twice to double check my measurement and this is the result. If I rotate the crank twice until the dial reads .050":

http://forums.pelicanparts.com/uploa...1519622759.jpg

Case seam is just shy of notch. Maybe a couple of degrees?

http://forums.pelicanparts.com/uploa...1519622759.jpg

Conversely, if I rotate the crank clockwise twice until the crank pulley is at Z1:

http://forums.pelicanparts.com/uploa...1519622759.jpg

Then my lift measurement is short .005" (.127mm):

http://forums.pelicanparts.com/uploa...1519622759.jpg

What am I doing wrong?

Thanks in advance!

Why are you even involved or concerned with .fifty, especially on a metric dial gauge
The spec for the cam is a variable, say +/- one mm.
Why are you reversing the spin direction to get to your setting. You have to come up to the setting from clockwise so tension is on the chains with no slop
Set the left cam then match the right to it. Start with both cams keyway up and pinned then make your settings.
As long as there is judgement on the pulley to centerline, there is always some variable.
Bruce

Thanks Bruce. I will try again, not reversing the spin direction (only clockwise) and see if that gets me closer.

I know there is inherently some backlash stack-up in the timing gears and the chains and sprockets so i figured if you back it up far enough (counterclockwise) you could then rotate clockwise and take up all the backlash well before getting anywhere near Z1. At least thats what I thought but it doesnt seem to be working that way.

Each pin setting has an inherent slop of .15mm approximately
I always load the left cam to the number that appears as I rotate the cam clockwise to press against the pin. Now match it to the right cam. Sometimes, to get the number you want you have to move the gear inside the chain one tooth to come in the number.
Now, according to Stompski's you tube, he sets the number on the dial then tightens the bolt to spec. Therory being it holds, where I lock it against the direction of travel

Bruce
Bruce

Bruce,

I was not using the pins and cam gear holes to fine tune my setting. Pretty elementary mistake I guess. Anyway, I got my overlap dialed in per John Dougherty's recommendations and I am good to go. Thanks for the help.