Link: Crane Cams
Here's a link to Crane Cams PDF on setting cams.
http://www.cranecams.com/uploads/instructions/803_.pdf
Yes in this case, the events are based on the tappet beginning & ending when it's .040 off the base circle.
Note that in the Crane reference, they call out .050 tappet rise. That is determined by cam grinder. Some advertise a lot of duration but it might be measured at .015, whereas a cam with less advertised duration might actually have more, if it's measured at a larger tappet rise number.
Simple now right?
Glen
--Previous Message--
: Sorry, I am still confused.
:
: I obviously don't have the book you
: have listing timing numbers. Is that
: something I can access online?
:
: You said the 0.040" is tappet rise
: measured off the base circle. I got
: that. You went on to say that it is
: the valve is considered
: "open" at that point. Are
: you saying that the duration of the cam
: would be measured from 0.040" lift
: opening to 0.040" lift closing? I
: must really be misunderstanding
: something then. Take a look again at
: my graph. (link this time instead of
: embedded graphic)
: Doug's Chart
:
: The vertical axis is lift off the
: tappet, the horizontal is crank
: degrees. For 0.040" lift on
: opening my crank is at TDC. For
: closing 0.040" is at about 220
: degrees. That's a lot less than the
: 256 duration I have seen quoted for
: stock cams and the opening clearly is
: not 18 BTDC. This is with the cam set
: for intake peak at 110 ATDC.
:
: If I were to set the timing based on
: the zero overlap at TDC it would still
: not be close to having 256 degrees of
: duration from 0.040" to
: 0.040" and the opening would still
: not start at 18 BTDC.
:
: As I said, I am very confused. The old
: chain and pulleys go back on tonight
: for a sanity check.
:
: Thanks for hanging in there with me!
:
: Doug
:
:
: --Previous Message--
: The .040 is out of the book that lists
: the cam timing numbers. It is also
: referred to as "tappet rise",
: simply that much off the base circle,
: it is the starting point that valve
: action is measured from. It is measured
: directly off the cam lobe. Set cam on
: base circle, set indicator on your
: checking tappet, zero it, rotate cam
: until checking clearance is achieved,
: .040 showing on the indicator. THAT is
: the point at which effective MEASURED
: valve motion begins, and ends as it's
: closing and it's .040 from zero on the
: indicator. The opening & closing
: ramps don't do much, there is a lot of
: cam rotation in degrees for slight
: valve lift as the valve assy starts
: accelerating. Once it gets going, it
: really gets moving and this is the
: point that matters.
: Disregard the rock check for now until
: we have the base timing correct.
: If we did a graph of it, we would see
: the inlet start to open when the tappet
: has risen .040 off the base circle, and
: we would be at 18 degrees BTDC.
: I'm not a very good explainer sometimes
: but we'll get it!
: g.
:
:
Responses