I've always been curious about this. Yeah I get the TDC and timing advance, timing retard, but....what do these degrees actually measure?

My guess until now has been that it measures the angle of the rod relative to the position and angle of the rod when it's at TDC.

Here's my professional diagram of what I'm trying to say:



So z¡Æ representing the advanced timing and y¡Æ representing the retarded timing in degrees.

Someone help out this lost soul.

Jay Kim

 

I thought it was degrees of the crank. Anyone know for sure?

 

Also what's the relativity of cam timing to ignition timing?

Jay Kim

 

It all revolves around crank position. To say 10 degrees ATDC is to say that the crankshaft has rotated a total of 10 degress past vertical after piston TDC. Anytime you hear a degree position it's relative to the crankshaft.


AllMotorMonster- Cam timing and ignition timing are also expressed in degrees relative to crank position. To retard either ignition or cam timing is to move the event further forward in time, to advance is to do the opposite. For example, 14 degrees base ignition timing is to say that the spark plug is sent electrical input at idle when the crank is at 14 degrees BTDC on the power stroke (or 176 degrees after the onset of the compression stroke).

 

Crank angle

 

Texan answered this correctly, but I'll add a little to it. A circle has 360 degrees. To understand why it is 360 picture looking down at a circle or draw one that is cut into four equal pie shaped pieces(a circle with a cross through it). The angle of any two adjascent straight lines is equal to 90 degrees. If you multiply 90 x 4 you get 360. When dealing with ignition timing, your flywheel is this circle. At TDC on the flywheel with the ignition rotor pointing at the #1 post on the distributor cap, the #1 piston is at top dead center of the compression stroke. On most Honda motors that I know of, for each 1 degree of cam rotation is equal to 2 degrees of crank rotation.

 

You would be correct sp: The cam turns at 1/2 the speed of the crankshaft.

 

This is exactly what I was looking for.

I love Honda-tech.

Jay Kim