Over the last few months I thought I had read every document online about the XJ timing chain procedures, but when I rented the tools to do the job myself the kit came with a tool I hadn't seen reference to: #303-654 Variable Camshaft Timing Oil Control Unit Setting Tool.

Curious, I started searching for links about that tool and found the attached Timing Chain PDF, which covers much of the same ground as all the others plus a step that is missing from the rest that seems to me might be an important one, namely retarding the camshaft oil control unit before tightening the VVT unit bolt. This step is the purpose for tool #303-654 and since this might be a critical step I thought I'd share it.

This document was posted on a Q&A site for the general public to access freely. The step is referenced on page 14 of the pdf.

If anyone can comment further on the nature of making this adjustment when replacing the chains I'd love to know what it is all about.

 

That has been previously refered to as "unwinding" the vvt. In other words, assuring that it is fully in the unadvanced position. Several folks have reported having timing wrong after failing to do this step.