There are a couple of symptoms that may indicate a concentricity issue. The first is, if there is any reddish rust residue in the coupling splines, which is an indication that the splines are wearing from misalignment. The second is seen when logging the Position and Reference signals with a Consult or other tool that can log from the OBD port. A graph of these signals should look like clean lines plotting the RPM, however, if the plotted lines show any divergent scatter (buckshot pattern) from the lines at any RPM, this is a classic sign of CAS backlash. As the coupling backlash vibrates, the CAS is advancing and retarding relative to the engine’s actual position, causing the spark timing to be presented to the engine as excessively retarded and more serious, excessively advanced which can cause detonation.
CAS drive pins have never been available separately from Nissan, however JWT makes a Chromoly CAS drive pin that is available.
Measuring for CAS concentricity can be done in the car, however, the CAS unit and the CAS drive pin will probably need replacement, if wear and or misalignment are found. Replacing the CAS drive pin will require the camshaft be removed from the engine. Changing out the CAS drive pin is explained at the end of the instruction below.
If any of the above symptoms are apparent or if you are building a high performance VG30DE(TT) engine, the following CAS drive alignment inspection and correction should be done:
1. Indicate the CAS register using a last-word indicator as shown. If the engine is still in the car, remove the left side timing belt cover, the CAS, and one of the cam sprocket bolts to allow a magnetic (or threaded stud) base indicator stand to be attached to the cam/sprocket. Remove the spark plugs for easy engine rotation. Set up the indicator so the contact ball is touching the inside surface of the CAS register circle. It is not important that the indicator stand be centered on the cam, as the cam will rotate and the contact ball will stay concentric relative to the center of rotation. Rotate the engine and mark the 2 points of highest eccentricity and the amount at each point. If the total indicated run-out (TIR) is more than .002”, you will need to correct it.