Date:         Thu, 20 Jun 1996 11:33:59 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         eugp@uclink3.berkeley.edu (Eugene C. Palmer)
Subject:      Re: Why adjust valves? 

So what I understood from your note is that you normally
>       have to change all the valves each time you adjust them,
>     I also assume that they have all drifted about the same amount.
>    If this is true, this would indicate some sort of wear mechanism.
>   The 'slipping' case would infer that most valves would be fine, but a few
>  would require adjustment, and the adjustment required could be very
> different valve to valve.
>
> Could the list memebers who have done this often comment on which of the above
>cases they would say is the norm?
>
>Bill Crick 

AHha, valves.

We wish valve adjustments were from drift.  Unfortunately they are from
wear.  Wear exists all along the valve train, starting at the camshaft
bearings, camshaft lobe, then the lifter face, the fit of the lifter in it's
bore, then the lifter socket where the pushrod contacts, then the inner
pushrod end, then the outer pushrod end, then the rocker socket, the rocker
bushings on the shaft, the rocker tip, the valve tip, the valve keepers, the
valve keeper grooves, the spring retainers, the seating surface of the
spring, the guides, and finally, the valve seating surface and valve seat,
and the fit of the seat in the head.

So, there is wear going on all along this path.  The most catastrophic wear
generally occurs on the seat itself.  Heat being the primary cause of this,
and accelerating the process severly.  Cast iron valve seats being the one
of the reasons lead was added to gas, luckily there are almost no cast iron
seats in use, except in extremely cheap rebuilt heads, and old american cars.

The best thing you can hope for is that, if your engine is a cool runner and
not over-revved, the valves will barely, or in the case of some bugs, hardly
ever move.  This is a good thing indicating a healthy engine destined for
long life.  On the other hand, driving a loaded bus at freeway speeds in the
heat up mountains and stuff, even a well built engine will suffer seat
degradation after a few hundred miles.  I know I'm in for trouble when I set
the valves one day, and the next morning they are .002, .003, or worst of
all .005, tighter.  This is serious wear of the valve and seat, and
indicates overheating and bad things.  When the engine is new, settling of
the parts is to be expected, and is why the valves should be set a few times
in the first 1000 miles.  Especially right after start-up.

Do you feel better now?  I doubt it.  Hydraulics come to mind here, and
maybe someone can say how great they are.  I'm feeling a bit better because
I realize that I can spot problems with the heads with the solid lifters,
and with hydraulics you might not get the chance.  Valve checks are your
best look at the health of your aircooled engine.  Big adjustments, bad;
little adjustments, good.

Eug,
'71

PS, I just tore down a stroked, 90.5 cylinder, Dellorto'ed, "professionally"
built bus engine.  It broke the #3 exhaust valve top off and caught it
between the crank and case, (after going through the top of the piston)
breaking a hole in the top of the case.  Cause, in my opinion, was the use
of a high lift camshaft on stock heads with stock springs.  As well as
having too high a CR.  There were very thin shims under the cylinders in an
engine that needed at least .140".  This thing must've screamed in it's time
though, and probably was floating it's valves often.

Lots of magnesium for the next CCC though.