Michael-
You comments are really helpful
>First, it might be a bit difficult to get a truly accurate measurement
at the pushrod (it is long and a bit wobbly, and the follower end is
rounded. But, the best measurement would be done at the cam itself.
I agree but at this point I am trying to avoid pulling the head this
season. I tried really hard to carefully align the push rods and the
dial indicator( on a magnetic base) and except for lobes 2 and 3, all
the readings, taken 3 or more times each, came out .278-.280 so I think
its probably an accurate measurement. On 2 and 3, if the measurements of
.252 and .265 are below the others, then the push rods are probably not
getting hung up. Is there any other cause of lower lift than wear or
mismanufacture ( seems odd just these two)? Can the cam follower
(tappet?)wear or be the wrong size?
>With the nominal 1.5:1
rocker ratio, the total lift would be ~ 0.420", which is definitely not
stock.
I read a reference in Richard Goode ( Goodeparts) catalog that the stock
ratio is 1.46, which when applied to the .278 I seem to have, gives
.40588 effective valve lift. The lift referenced in Ted Schumachers (
TSI website) cam selection guide of .405 is for the S2 cam which I have
seen referred to as a pretty typical "street" cam. Make sense? The S-4
cam is .410 which when reverse extrapolated at 1.46 gives .281 lobe
lift, which isn't a whole lot different, but thats a pretty aggressive
cam an not likely to have been put into _this_ car.. When I pull the cam
gear, do you think there will be some reference on the front bearing of
the cam for what it is?
>As for checking duration, yes that can be done with a dial indicator
and
a degree wheel, but is best done at the cam. All that's necessary is to
install the degree closed to indicated top dead center, put the
indicator on, turn the cam, or engine until the indicator just registers
a change, note the degree reading, and then rotate the cam, or engine,
in the normal direction of rotation until the indicator returns to zero,
and then note the difference in degrees on the degree wheel. That's the
absolute duration.
What duration means then is the degrees of turn of the _cam_ that occur
betweed when the lobe begins to lift and when it drops back on the other
side to zero?, ie watch the dial indicator rise from zero then return to
zero and the number of degrees that have passed is the duration? ( or
do you measure the degrees of turn on the crank?)
Checking and effective duration are measurements of the curvature of the
lobe? That is, how quickly the valve opens or closes vs its absolute
peak open position?
>Note, too, if you've got the degree wheel and indicator already out and
installed, it's also a good time to mark absolute TDC, using the
indicator to establish the piston TDC point, and then comparing that to
the existing pointer, then bending or filing the pointer to show true
TDC in relation to the crank markings.
Yes I've looked at that and it appears dead on...( must not have been
Monday morning in Coventry when engine 21821 was assembled ;-)
>As far as assembling everything, the timing marks are set for TDC at
#1,
so it doesn't matter what other cylinders are doing at the time. If both
#1 exhaust and intake lobes are down at approximately equal angles to
the cam centerline, the general orientation of the cam will be correct
for assembly when the #1 piston is at TDC. From that point, it's just a
matter of getting the cam sprocket in the right orientation to get the
cam timing as close to right as possible.
Are you saying eyeball the #1 and 2 valves ( cyl 1) to see if they are
even at TDC on the firing stroke?
Timing is actually at the root of all this. My concern is that a hot cam
has a different timing orientation than a street cam. One issue I have
wth this car is to get the motor running strong and smooth ( considering
the Weber DGV's) a good road timing will wind up with an advance of
close to 23-25 degrees! I've been thinking that the PO did not orient
the cam correctly, unless he was following a cam manufacturers
guidelines for cam advance on the hot cam. So I need to figure out what
the cam orientation should be at TDC, turn the engine to get that set
and then look to see how far off TDC is in order to conclude that there
is a misorientation.
Keith
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