I have often wondered about this question, as an engineer ; if the lift at
cam is .3 , a change of .003 on push rod side (.0045 at valve) is one part
in 100, 1 %---- I have a very hard time believing it matters at all to
anything, performance wise, .except one extremely critical thing . If in
the excessive zeal to "get it perfect", you set it too tight , exhaust valve
will not close tightly, (only when under high loads) which burns exhaust
valve or seat, and down you go--- big time . Head gets trashed . The stem
extends when hot ,why the exhaust setting is more, OEM .
I went through this on an Onan generator with the equivalent of 1,000,000
miles (figured by hours) powering an isolated home, which lunched an exhaust
valve badly on propane (no lead) ; the symptom at first was lost power,
gradually reducing exhaust valve tappet clearance , which I thought was due
to adjustment not holding (manifested as loss of power and compression), so
I reset gap to factory (.017 cold) -three times,-- it had closed to like
.012; I had rebuilt engine some years prior (rings) and obsessed about
getting the tappet clearance EXACTLY RIGHT. Now it is on second (stellite)
valve, I added .003 (,020 cold) on purpose to be sure valve closes. These
are Onan numbers, not for Chrysler. Zero problems with this, last ten
years. Sounds like racing cam guy had same thoughts as I did-loose far
better ---by 1000X--- than tight. ; that Chrysler spec is a LOT of
clearance , big number for "HOT" ---and then, what is hot? Exhaust valve
stem at idle is ~ same temp as block, but really far hotter (????) at WOT ,
so setting it "hot" smacks of arbitrary BS, besides being a mess. While I
cannot remember details right now, I remember setting up a slant six cold
rather than hot with some added number I got somewhere. That number can be
figured out approximately by taking highest temp exhaust valve can ever be
(?1000F?) and length of valve stem times expansion rate of steel with temp ;
I would expect all push rod V8's not that far apart either, on this---
particularly if you add .003 . See brand X or aftermarket cam cold settings.
I do not understand how setting it hot at idle is more effective than
setting cold, if you have cold number.both are building in or allowing for
the expansion of exhaust valve stem when hot at WOT (.026?) , adding a
little more gets you out of all danger, even from a cold setting..but we
often do not have cold setting..but it is there , technically. As some
engines only show cold setting! Measure it cold, on this, after and before
setting it hot? Find out?
Some will scream heresy at this, but as described ,this H already burned all
the exhaust valves once. I really doubt unleaded is the reason..more likely
valves were set too tight , someone going for perfection , (or used hot
numbers cold) and mixture lean at WOT (which can happen on carbs with
alcohol based fuels , need more fuel than real gas for given air flow
--which really ought to be rejetted for) ; I have many cars on unleaded,
have yet to encounter burned seats, except in alarmist magazine articles. .
But I did destroy an exhaust valve over what must have been a too tight
setting, leading to no cooling of exhaust valve( it cools edge by
transferring heat into seat while tight on it (and by stem cooling) . By
the way, the cylinder side of that totally burned valve was still perfect ,
plain cast iron. And lead problem was supposed to be about recession, or
pounding into head, (which reduces tappet gap) ---not about burning. (or
"pounding into head", for that matter..why or how would lead possibly change
that?) With hydraulics, no impact at all to have receded valves, but might
lead to burning with solids if it takes up safety gap when hot .
So if you set it hot at idle, use Chrysler numbers, and do not worry if a
little loose ,,,but never tight.might even set loose. You might measure
cold first, before touching it , get that data for each valve, then do hot,
also measure and write down hot before setting , you will know difference it
changed due to idle temp--- within the .003 loose, to do it cold next time.
Just not as critical to idle or performance as made out to be, when running
along, IMHO..cannot be. But if you set it too tight while messing with it
, you are toast.
John
PS agree 100% on distributors, they are in poor shape generally, after
storage , advance gets locked up and / or sticky . Often diaphragm is bad
which mity vac can find right away.
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx]
Sent: Friday, May 09, 2014 11:06 AM
To: Listsaver 300 Club
Cc: Gary Nelson
Subject: [Chrysler300] 300H valve adjustment[Non-text portions of this message have been removed]
I have been working gradually towards getting my 300H running as well as I
can.
This forum has been a terrific help in many ways.
A big step was the professional restoration/rebuild of both carbs, which
followed the earlier massive and total restoration of the braking system,
including installation of the correct double diaphragm booster. (Booster
Dewey of Portland discovered that problem.)
Recently, I had the distributor rebuilt which resolved my runaway idle
adjust problem and is generally a great improvement.
The next thing I am suspicious of is my valve settings.
Unfortunately, the camshaft in the car is not the stock 300H camshaft, but
instead is one which a well respected
racing engine shop in Illinois installed in 1982 because of a fear that the
engine would not be able to run on unleaded gasoline . (They were right in
a way because a few years later I had to have hardened seats installed on
the road.) It ostensibly lowers the compression ratio.
The camshaft is a Barnes Racing Cams Design no 275 (I have the spec sheets
for it) I do have a stock 300H camshaft which I eventually use to replace
it, but not this summer.
I had a well meaning friend stop by last year who was going to help me get
it running right,. He managed to destroy all the old car linkages by
bending them etc. and wanted to modify all sorts of things-in the process
though, we got into a valve adjustment exercise one might and he was
convinced the settings specified were wrong!
So my next step is to set all the valve per the manufacturers specified
valve lash.
Chrysler 300H settings specified are .015 intake, .024 exh, set with engine
running.
Barnes F295 settings are .026 instake, .026 exh, set "hot"
I have no idea what settings I have which is why I want to verify it. I
suspect they may be stock 300H settings but the idle makes me think I have
some hot valves.
Question:
I do not think I have ever set these valves hot with the engine running as
specified in the shop manual.
I suspect that makes an awful mess.
Is it that important?
If you have set the valves hot and running, I would like to hear how it
went.
Thanks, Mike Moore
--
Ray Jones. Y'all come on down an see us. Ya hear?
__._,_.___
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