Date: Mon, 23 Jun 2003 20:27:34 -0700
Reply-To: Tom Young <tomyoung1@ATTBI.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Young <tomyoung1@ATTBI.COM>
Subject: Re: engine noises
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----- Original Message -----
From: "Dan Erlandson" <danoer1@eclipse.net>
To: "Tom Young" <tomyoung1@attbi.com>; "Vanagon" <vanagon@GERRY.VANAGON.COM>
Sent: Monday, June 23, 2003 7:20 PM
Subject: Re: engine noises
>
> > That "rock hard" effect is exactly what you want. The fact that the
others
> > are compressing indicates they haven't pumped up yet. I once redid the
> > heads on my Vanagon and it was probably a week before all the clacking
went
> > away. Drive on.
>
> Thanks for the reply Tom... I've been searching the archives on engine
> noises and there was your reply!
>
> But if what you say is true then why can't I get a .006 feeler gauge in
> between the top of the valve and the screw on the rocker arm?? Is the
valve
> damaged??
I'm not sure what the "magic" of .006" represents. I know Boston Bob
recommends it for pumping up hydraulic cam followers, but where that figure
comes from, I don't know. Think about it: you've got a cast head, places
for the valve seats are machined in, then valve seats are pressed in, then a
"valve job" is done, grinding away some amount of material, and valves,
which probably *aren't* all exactly the same length, are placed in the head.
To my way of thinking it would be a complete miracle if the valve stems all
ended up at *exactly* the same height, such that a feeler gauge between the
stem and rocker arm off all the valves resulted in the exact same
measurement.
Don't get me wrong, a "well-done" head *should* end up with valve stems all
more or less at the same height. Too, if you periodically check the valve
clearance and find the stem/rocker arm distance "tightening" you may be
looking at a valve seat that's receding in the head or a valve stem that's
stretching. But I don't know if you're dealing with new heads, used heads,
"mystery" heads, or whatever, so I don't know how to answer you here.
Depending on the circumstances, I might reason as follows: "This cam
follower is completely pumped up. The largest feeler gauge I can get in
here is .00X inches. I'll finish the set-up on this follower (somewhere
between 1 and 2 turns, depending on your religion) and let the others run as
is (I'm assuming .006") until they pump up. When they're all pumped up I'll
set them all and then come back is X months and check the distance between
the valve stems and rocker arms. If the distance has changed *materially*
I'll think about what that means. In the meantime, I'll drive."
> One of your earlier emails had said that you can tell TDC by
> looking for both valves being closed, meaning that when I look at the
rocker
> arms at TDC there should be flexibility there, no? The pushrods should be
> retracted somewhat, allowing the valve spring to expand up, away from the
> cylinder, i.e valve closed, right? This is not what I see at TDC for
> cylinder #1 exhaust. The pushrod seems extended a bit, enough that I
can't
> get a feeler gauge in there... All of the other cylinders seem to be as I
> would expect for the valves closed... rocker arm flexible and pushrod
> retracted, thus I can get a feeler gauge in there.
I'm not exactly following what you're saying here. Both valves are closed
when the tips of the rocker arms are at the top of the "arc" they make as
they move up and down. If you can get someone to turn the engine over as
you look at a bank of rocker arms you'll get what I mean: the tips of the
rocker arms move "down" (toward the center of the engine) as they push open
the valve. Then the move "up" (away from the center of the engine) as the
valve closes. When they reach the top of the "arc" they stay where they are
briefly as the cam follower rests on the "back" of the cam. TDC on the
compression stroke is when both rocker arm tips are at the top of the arc
(valves closed) and the piston is at TDC.
If you're running the valves "loose" (i.e., some space between the rocker
arm screw and the valve stem) then, yes, I'd expect to see the pushrods
retracted somewhat, but not necessarily all the same distance given all the
variables discussed above, plus the fact that some followers are pumped up
and some aren't.
---------------------------------------------------------------
Tom Young '81 Vanagon
Lafayette, CA 94549 '82 Westfalia
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