Wednesday, March 6, 2013

Getting a degree: Using basic math to confirm ignition timing

Just when I thought I had escaped the trappings of high school math it comes back to haunt me. I was a poor student in school and slid by in math class where, much to the dismay of my teachers, I would use logic to solve problems rather than apply the procedures they were teaching. In the end I would get the correct answer so I figured I must have been doing something right but my teachers were never pleased.

Getting back to the world of Dino's I wanted to confirm some details of the static ignition timing but lacked a degree wheel with which to take my measurements. In the end a degree wheel is nothing more than a circle with graduated markings on it. In my case all I needed to do was take one measurement, that of 40 degrees before top dead center (BTDC). The circular harmonic damper on the crank was to serve as my degree wheel using some basic high school math and logic. Here is how I did it:

Step 1: Measure the diameter of the damper in mm

Step 2: Use the formula pi(d) with d being diameter to calculate the circumference of the damper

Step 3: Divide 360 (the number of degrees in a circle) by the circumference and I would get a dimension in mm that would equal 1 degree

Step 4: Multiply 40 (the number of degrees I needed to measure) by the result of Step #3 to get my final measurement. In this case it was 46.58mm

Step 5: This measurement was then transferred to a piece of tape where I accurately made 2 thin lines exactly 46.58mm apart.

Step 6: I used a dial indicator to accurately find TDC of the #3 cylinder as per the shop manual and then installed the tape on the outside of the damper using the factory indicator needle for reference.

Step 7: Making sure that I observed my points from exactly the same place to avoid any angular distortion I checked all of my measurements and confirmed my ignition timing.

The photo below should fill in any questions and this technique can really come in handy when a degree wheel is not available. I wonder what my high school teachers would think :)

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