Cam Timing Questions.

Groovy911SC · 10-11-2004, 06:04 AM

I am timimg the cam for a 3.0 ltr. engine. The crank is a standard/standard, rods stock, pistons are the J&E 9.5/1. I've kept this rebuild a stock as possible. The cams were reconditioned as were the rockers.
The question I have is... when I set the crank at Z1, align the cams with the punch (small dots) straight up, install the dowel pins, place and then tighten the cam nut, adjust the left side intake rocker to .010mm and rotate the crank clockwise... right before the crank reaches the Z1 mark (approx 350 degrees or so) the indicator starts move. When I reach the Z1 mark, 10 or so degrees later, the value on the dial indicator reads .10 mm - not 1.0 mm or .01mm.
In Waynes book it suggests that you should reach the "intake valve stroke in overlapping TDC with 0.1mm valve clearance" before you reach the full 360 degrees.
My problem is that to reach the range of the "intake valve stroke in overlapping TDC with 0.1mm valve clearance" which is between 0.9mm and 1.1mm for my engine, I would have to move the crank past the Z1 mark by some margin.
My guess is I've made some mistake with either identifying my engine, placed the cams in the wrong sides, have received the wrong cams back from the reconditioning process or am freaking out over nothing...
Any help or information would be greatlt appreciated!!!!

ChrisBennet · ChrisBennet's Garage

I think you are worrying for nothing. When you put the pin in the sprocket initially you are setting the cam timing very approximately. On the 911 motors I've done (CIS and Motronic) I've always had to move the pin a least a couple of holes from the original position.
Of course, if aren't using something to keep the chain tension tight (the tensioner itself is not sufficient) the extra slack will probably throw things off.
-Chris

Groovy911SC · 10-11-2004, 08:03 AM

Thanks Chris!

I have the sprockets snug with the ole vice grip method on the left side and a mechnical tensioner on the right side.
I guess I could proceed with the timing and then perform the valve to piston check extensively to determine if I'm off.
What is your opinion on the valve to piston check? If I'm within limits I should be okay?

Eagledriver · 10-11-2004, 09:07 AM

I think your timing is just a little off (that's what this process is all about). As long as you are careful to turn the engine slowly and with not too much force when the piston is near TDC you will not damage anything even if the valves do hit the pistons. If you do the timing with only the intake rocker for #1 or #4 installed you can watch to make sure the intake doesn't open too much as the piston approaches TDC.

-Andy

Groovy911SC · 10-11-2004, 10:00 AM

My next question is... If I set the crank at TDC, and adjust the cam (without the dowels on the sprockets, making sure the crank does not move) to reflect the .9mm-1.1mm range value, am I cheating? Is this what you are suposed to do in the first place?
Sorry for my ignorance... I really want to learn and know this process. Also, I don't want to grenade my engine!

Eagledriver · 10-11-2004, 11:53 AM

Yes, that is an ok way to do it. You must check it again after you put the pin back in because something may move while you do that. It can take several attempts. What I do is figure out which way I'm going to move the pin and move it one or two spots in that direction at a time. There is also enough slop in the pin to move the timing enough to get it spot on after you find the right hole.

-Andy

ChrisBennet · ChrisBennet's Garage

Keep in mind that if the cam is in the position of pressing on the rocker, the cam will want to turn/unwind when the pin is removed.

To avoid having the cam spin, I turn the crank a little CCW so the rocker isn't putting pressure on the cam, then I move the pin.

I prefer to mark the initial pin hole and then move the pin one hole at a time, snug the bolt or nut up some and remeasure. If it looks good, I tighten the cam bolt/nut to final torque and remeasure.

Check out this thread: Cam Timing Questions

-Chris

john walker's workshop · 10-12-2004, 07:20 AM

on the engines with cam bolts instead of nuts, you have to do it that way. turn the crank until the cam gets where you want it, pull the pin. Z1 the crank again, insert the pin, snug up the bolt, and recheck. you can do it either way with cams with nuts.

Groovy911SC · 10-12-2004, 07:24 AM

Okay, Thanks John!! Thanks everyone! This certainly helps!