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.
--Previous Message--
: Thanks but I am not clear on this yet.
:
: Where did the 0.040" value you
: mentioned come from and where is it
: measured? Is it the gap between the
: rocker arm tip and valve stem (not
: applicable to me since the head is off)
: or is it the lift at the cam lobe? If
: it is the gap at the rocker arm tip I
: would need to compensate for the rocker
: arm ratio to be able to apply this
: value at the cam lobe. (i.e. a
: 0.040" gap at the rocker arm to
: valve would equal 0.027" lobe lift
: for 1.5:1 arms).
:
: I hate to beat a dead horse but would
: you take a look at my graph below and
: help me interpret it? The chart shows
: the lift I measured on my engine with
: the cam timing set to place the LCA for
: intake #1 peaking at 110 ATDC. I know
: that there is no scale marker at 110
: ATDC but you can pretty much see that
: the intake does peak there. You can
: also see that the exhaust peaks 110
: degrees before 720 degrees on the
: chart... where it should be. What I
: cannot get my head around is that the
: overlap on the lift for valves 7 &
: 8 occurs 4 degrees BTDC (where the red
: and blue traces cross just before 720
: degrees on the chart.
:
: Can you explain what you meant 3 posts
: back (your 9:30 post) where you said
: how you would handle this? " For
: the setup I would use opening/closing
: points, if they = 110 lobe center.
: "
:
: I think I am there, I just don't
: understand why the overlap is not
: happening at TDC like you and the
: Bentley manual suggested it should. If
: I set the overlap to occur at TDC then
: the LCA for intake number one is going
: to be about 4 degrees late. It sounds
: to me like I am looking at a trade off
: which is why I am going to fit the old
: pulleys and chain again and see what I
: was running before taking the engine
: apart.
:
: Thanks for helping me try to understand
: what I am looking at.
:
: Doug L.
:
:
:
:
:
:
: --Previous Message--
: The checking clearance is also used in
: calculating the "advertised
: duration", a meaningless term
: unless you have the checking clearance.
: A grind with the clearance at a lower
: lift value would measure more duration
: overall.
: Most important is the acceleration of
: the ramp profile, the goal is to open
: and close as quickly as possible, w/o
: exceeding the limits of the valve
: train.
: For a stock street engine, opening and
: closing should equal calculated LC, 18
: + 180 + 58 = 256/2 = 128 - 18 = 110,
: and you should find the opening/closing
: points are correct at the .040 called
: out.
: Glen
:
: --Previous Message--
: OK Doug, good question, and a simple
: answer.
: When a cam is ground, the
: opening/closing ramps are fairly
: gentle, in terms of valve acceleration,
: not much opening/closing action per
: degree of rotation until it takes up
: the running clearance and gets the
: initial motion going and it gets on the
: actual part of the lobe where there is
: real acceleration. The cam designer
: will call out a spec on this amount of
: valve lift (checking clearance) to do
: the initial setup. There is no
: universal standard for the checking
: clearance, I've seen as low as .015ish
: to over .050.
: The checking clearance is vital to know
: when setting up a cam, short of lining
: up the dots!
: HTH, let me know if not.
: Glen
:
:
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