if a head is milled, do you set TDC with the cam at 0 Degree setting or at the advanced Degree setting? here's a pic to explain what i'm asking.
**edit

heres a better pic of what i'm asking.. this should be more clear.

If you rhead is MILLED, do you set TDC with the INNER or OUTER marks of the CAM GEAR??




Modified by boonacka at 12:02 PM 9/1/2006

 

good question. Bump 4 u.

 

on the adjustable gears, the outer ring will move clockwise if you keep the cam in the same position - milling head or block 1mm (about .040") will change the camshaft by slightly less than 1 degree on a D-series engine and slightly more than 1 degree on a B-series

 

ok.. but my question still is- at which setting (configuration) would you use to set it at TDC???


Modified by boonacka at 7:52 AM 9/1/2006

 

someone must know.

 

bump good ?

 

since the cam <U>must remain in the same position, relative to the crank, for zero degrees advance or retard</U>, you would use the TDC mark on the inner part of the gear - the marks on the outside ring will be in different locations depending on how much the head is milled, however, the camshaft itself (and the inner ring) must remain at TDC when the crank is at TDC - the marks on the outside ring only work when the head is not milled - if you tried to align the crank mark at TDC and then align the cam mark at TDC on the outside ring, you would find that the belt would have slack in it on the front side - this is because the length of the belt between the crank and cam gears remains constant, but the actual distance got shorter with the milling - when you remove the slack from the belt (while keeping the cam at the same position relative to the crank) the outside ring of the gear has to rotate clockwise by the amount that the head is milled - when you rotate the outside ring, the marks on it rotate with it and no longer align with anything - in order to install it correctly, you need to have the cam gear at zero and with the crank gear at TDC, align the cam gear mark with TDC - put the belt on (it will have slack at the front) - now comes the tricky part - <U>without rotating the camshaft</U>, loosen the bolts holding the two parts of the cam gear together and rotate the outside ring clockwise until the slack is out of the belt and then retighten the bolts - how far you have to move it in degrees will depend on how much the head is milled - the degrees it moves is fairly easy to calculate by using a simple math formula for the Properties of a Circle, where:

Angle A (in degrees) is = 180a/pi(r)

with “a” being the length of the arc or distance that gear rotates (equal to amount milled) and “r” being the radius from the center of the cam gear to the belt.

On <U>B-series</U> Honda cam gears, the radius is 51.5mm or 2.0276”. Plugging the numbers into the formula you will get:

Angle = 28.2579a

Substituting into the formula, for instance with a head milled 0.020” the camshaft will rotate 28.2579 x 0.020 = 0.565 degrees clockwise.

On <U>D-series</U> Honda cam gears, the radius is 57.5mm or 2.2638”. Plugging the numbers into the formula you will get:
Angle = 25.3096a
Substituting into the formula, for instance with a head milled 0.020” the camshaft will rotate 25.3096 x 0.020 = 0.506 degrees clockwise.

 

wow you went a little farther than i expected. nevertheless it is what i was looking for. aside from all the mathematical calculations, everything about it makes sense and is simple logic. Thanks for the clarificatioin JLI