The notch on the cam tower is a good rough indicator that can tell you if you need to adjust that timing. If you decide to adjust it, you use the more accurate measurement based on crank position when the #1 intake is at 2mm lift to determine what offset key you use and/or replace the timing chain.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.