Carrera Cam Timing

[Max911SC]

On my 87 Carrera, I removed and replaced the timing chains and rails. In the Bentley manual, there is a picture of both sprockets reading "930" at 12 o'clock when the engine is at TDC. However, on mine, the left side "930" is pointing at about 10:30 or close to 45 degrees. Do I need to reset this before I go on? If so, how do I do it? I know it also says to adjust the #1 and #4 valves before timing the cam. I did this part but I'm still not sure how I proceed. Also, is this what it means when you advance the timing? Just want to get it right. Thanks.

[Rot 911]

The Bentley manual gives a good description of how to time the cams. When you start both cams should have the 930 pointing up. You are going to have to loosen up the sprocket nut to be able to rotate the cam.

[Max911SC]

Is this done with or without moving the pulley?

[ChrisBennet]

You will need learn how to set the cam timing. It's very critical. When the cams are timed the "930" may not be exactly at 12:00 but both cams will point in the same direction i.e. if the "930" is at 1 o'clock on the left cam, the right cam will also have the "930" at 1 o'clock.
The pulley doesn't get removed for this operation, in fact you need it on there for the marks.
-Chris

[Rot 911]

Originally posted by Max911SC
Is this done with or without moving the pulley?

Max, I am getting the feeling by you asking this question that you have not completely read the instructions in the Bentley manual. It takes you step by step through the timing process. And you definitely need the pulley installed to rotate the engine and for the timing marks.

[Max911SC]

I read the Bentley but I want to make sure I am doing it correctly. The main question was do I move the left sprocket only, the one with the 930 on it, and how is this done. Since both "930" marks are not pointing in the same direction I am wondering how to set one without disturbing the other. The picture in the Bentley has you starting with both of these marks in the same position, which mine are not. Later in the process it says the left one should be pointing at 45 degrees which it already is. Sorry, but I've never done this before.

[ischmitz]

Max,

without going into all the details of how to time your engine here are some points:

Assuming you put new chains on your engine is not timed at all. The first step is to do the corase timing. The engine needs to be in TDC firing #1. Both cams need to point upwards. The slot for the woodruf key on the cams must face to 12o'clock. Most cams have a punch mark, or some writing on the front face that will help you determine the 12 o'clock postition. My left cam had two punch marks. One at 12 o'clock and one at 6 o'clock so I had to doublecheck the woodruf key position. This step is crusical before you procede with the fine adjustment. A mistake here could destroy the engine by bending valves.

Advancing or retarting timing ususally referres to the spark timing and not to the cam timing. I would not recomend to alter the cam timing from factory spec unless you clearly understand how to check valve to piston clearance on a 911 engine (interference design: Valve and piston occupy the same space at different points in time). As a hint the valve to piston clearance is not minimal at TDC.

Ingo