Vance---OK, let's see if the list wants to take part in a poll. Who is
experiencing valve seat recession? Who uses the lead substitute?
I'll keep score.
The check for valve seat recession does not necessarily require removal
of the head.. Nor the tedious task of finding a good place to measure
stem height. One can get a good idea if this recession is taking place
by just keeping track of the valve lash, from one check to the next
check.
By writing down the lash as found at each valve, before adjstment or
check, (as I always do) simply make note if any valve lash "closes up".
This is a strong indication that the valve is beating into the seat in
the head.
Of course if wear in the valve train is canceling out the recession
loss, then this could get muddy.
The idea here is that lash should never diminish as a normal part of
valve train wear. If a lash loss is suspected, keeping track of those
partcular valves would be prudent, as a valve that's not allowed to
close will burn.
Now. Who's experiencing lash loss?
Dick Taylor
Lead substitutes - Godsend or garbage?
Dick and Jim:
I think you will find
the belief in the need for lead substitutes
to be pretty polarizing. Some people swear by it, others think it's a
waste.
I am somewhere in the middle (wishy-washy is my middle name).
There is no doubt that lead in gasoline will protect valve
seats.
The lead is deposited on the valve seat and prevents the hot valve from
bonding to and lifting metal from the seat. There is also no doubt that
many engines have displayed signs of valve seat recession, and this sort
of thing was unheard of when leaded gasoline was around.
There is also no doubt
that many motors run just fine without lead, despite the fact that the
metallurgy of the head is vulnerable to erosion without the protection
of lead or something like it.
The question is - how
can I tell if I have an engine that needs
lead
or a lead substitute without a teardown? Well, you can't really.
There is always a risk, BUT I believe if you opening your motor
up,
and find no signs of recession that adding hardened seats is mostly a
risk.
That's because you weaken the margin between the valves, and you are
more
likely to develop cracks there. Hardened seats can fall out too,
particularly if the engine ever overheats.
My motor had absolutely
no signs of recession at 70,000 miles,
so I
left it alone.
I cut new valve seats and that was it. If I keep my engine
in tune, and don't let the mixture run lean or set the valves
incorrectly
then I believe that I will not see a problem. I think a few egregious
cases have put fear into the minds of the public.
As for determining if
your motor needs lead substitute, well, I would
measure the height of my exhaust valves using a caliper. If any of the
exhaust valves are 0.010" taller than the others, then I would start
using
lead substitute. But then, that's me.
How likely do I think it
is that I would find I need to add a substitute?
On a properly maintained motor with the correct fuel mixture, I would
expect
that one motor in 100 would benefit, maybe less. Let the
mixture go lean, let the timing get sloppy, and the odds
would
start climbing depending on how long the condition was permitted.
Just my demented ramblings....
Vance
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