911sc cam timing variation

[phil fleming]

I would like some advice as I have cam timing variation. The issue is on the left bank cyl 1-3 I have a timing of 0.96mm when I have the chains clamped (tensioner removed). I have adjusted this as I had to do a broken head stud on cylinder 3. When I reinstall the tension and check the measurements I am getting 1.04 mm still in range as the car is a 1981 SC RoW which should have 0.9 to 1.1mm spec.The Right bank timing on 4-6 with tensioner installed (I havent touched this side of the engine) shows 1.07mm so very close to the cyl 1-3. Why is there a variation? Is this normal due to different tension being applied by the tensioner as opposed to when I have the chains clamped up for timing check? Is it ok to have one side 1.04 and the other 1.07 ?

[stownsen914]

Yes you'll see a difference under tension vs. not. It's recommended to set cam timing with the chains under tension. The difference you are seeing for the left vs. right banks is small and normal.

[Ollies930]

I would be very surprised if you got the same measurement every 360*. The difference you are talking about is somewhere around 1/4* of cam duration. If you changed the locating pin on your cam sprocket, it would move a lot more than that.

[phil fleming]

thankyou for the replies - Not sure about the comment !/4 degree cam rotation. I am pointing out that the difference is on 3/10 of a millimetere difference in readings

[stownsen914]

I believe he is pointing out that such a small difference in valve lift results from a very small rotation of the camshaft - to the point of being within margin of measurement error.