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# True Tdc

### How to Degree a Cam

Discussion and questions related to the course How to Degree a Cam

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I followed the process as displayed but I'm still curious as to after I find these values. Add them together then divide by 2. Once the pointer is moved to face the sum value of those 2 numbers..Is true tdc that value in the operating direction of the crank? Or do you move it back to the markings on the sprocket to begin?

I'm not sure I follow your question? The key point to understand is that you'll end up with two marks on your degree wheel from the two places that the piston contacts the stop. True TDC is exactly in between these two marks. By adding the two degree values together and dividing by two, you'll find this value. At this point you can move your pointer or you can loosen off the degree wheel and rotate it to correct any error. If I haven't explained this clearly enough, please let me know how else I can help.

This also confused me at first .....

i think what kl1ne308 means is that after you have divided your two numbers and you Bend your wire to your required point on the degree wheel, it comes across in the course as if that point is TDC when in actual fact TDC is at 0 on the degree wheel. It’s confusing because you don’t actually move the wheel to zero you leave it at the point where you bend the wire.

took me a minute or two to work it out

Yup, move the wheel and/or pointer until the stop is contacted an even number of degrees with the crankshaft BTDC and ATDC.

Same principle if using a DTI - you want the same amount of travel of the guage at the same amount of degrees of rotation.