Mike,
I gotta go with Gene on this one. With cyl temps above 1800 Deg F there is no
oil to lube the valves! The lead
coats the valve faces and seats and keeps them from sticking to each other.
Newer engines have hardened valves
and seats (or stellite faced valves). Even if you grind the new style valves,
they will not last. (the stellite coating
is very thin). You may not have noticable compression loss on your engine yet,
but if you are running old "soft"
valves/seats, and unleaded fuel (any octane), you will! You may want to stock
up on valves/seats for your head
rebuild if you should come across some in the near future! (or just use an
approved additive)
Passnb4U@aol.com wrote:
>
> In a message dated 99-06-02 10:37:44 EDT, genedavis@tritel.net writes:
>
> << To: oletrucks@autox.team.net
>
> Terry White wrote:
> >
> > Mike,
> >
> > I am not by any means trying to lead anyone to believe that I am a
> > mechanic, but this is my experience.
> >
> > I bought my 56 in late 95, drove it almost everyday for 3+ years using
> > 92 and 93 octane fuel. I was told that sooner or later if the head
> > did not have hardened exhaust seats I would lose compression. Guess
> > what, I did. I have decided to put a newer model 292 because of
> > the lack of parts availability here in Alabama. My advice would be to
> > use the highest octane you can buy, drive it till you get a noticeable
> > loss of power, then look at the possibility of a rebuild, chances are
> > if you have the head worked now it will only put higher compression on
> > the worn cylinders.
> >
> > Just my thoughts..
> >
> > Terry White
> > 56 3100
> > Harpersville AL.
> >
> > >>> <Mushgilday@aol.com> 06/01 6:37 PM >>>
> >
> > How critical is it for these old engines
> > to be
> > fueled with lead additives? Is the overall performance diminished if
> > only
> > using an 87 octane with nothing added? I've been running my 235 for a
> > year
> > now and have yet to mix anything in with a fillup. Lately I have
> > noticed a
> > slight hint of exhaust smoke which was not the case last year. Oil is
> > changed
> > frequently and it's been tuned up lately. Any recommendations on the
> > use of
> > lead mixtures in the gas? Thanks
> >
> > Mike Gilday
> > 59 Apache Fleetside 3200
> > oletrucks is devoted to Chevy and GM trucks built between 1941 and
> > 1959
> >
> > oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>
>
> My $.02 on octane/lead;
>
> Higher octane is needed to combat detonation. Lead is needed for valve,
> especially exaust valve, lubrication. Confusing because lead is also a
> cheap octane booster. You need higher octane fuel if you have a higher
> compression engine, (hence 100LL for aircraft,- higher compression, high
> prformance, low end torque, opposed piston engines.) You need leaded,
> or comparable, fuel for top (valve) lubrication in older auto or
> aircraft engines.
>
> I am no expert, but have some experience with both truck and aircraft
> engines. It tells me that older engines, not designed to run without
> lead, need a lead replacement. If you have a engine that is not a high
> compression engine, and are getting some pinging,(detonation) check your
> timing before running higher octane fuels. Its alot cheaper to time the
> thing than to spend extra money on octane you don't really need.
>
> I did have a Fo#d w/ a stock 460 that no amount of timing work would
> stop from pinging. Had to run at least 89 octane in it.
>
> Help, or just confuse everything more?
>
> Gene Davis
> '58 GMC 1/2 T NAPCO
> '63 Cessna 182 >>
>
> My understanding in the lead is used to cool the combustion chambers,
> decreasing detonation. Lubrication comes from the oil, not the fuel.
>
> The use of hardened seats is to keep little hot spots forming from the
> possibility when the valves close, the valves kinda nick on the seat, making
> a little high knurl that creates a glowing hot spot, whick leads to pinging
> and seat recession in some cases.
>
> FWIW, my '235 run's at 3Krpm whenever it's driven (damn, I gotta get that
> rearend done), usually on 85-90 miles runs, each way. I have about
> 15-16Kmiles on it (don't know how many before I ran it), no apparent losses
> of any kind that I can tell.
>
> Mike
Mike is very probably right about lead and lubrication, but I can't see
how oil can lube a exhaust valve in the upper guide with cylinder temps
as high as they get. An aircraft IA Mechanic told me that lead does
most of the lube work on exhaust valves in airplane engines as the oil
in the guide turns to carbon in the upper part of the valve guide due to
temperature. Lead also forms a barrier between the valve and the seat
as I understand it, preventing metal to metal contact. I'm not even
close to being an expert on this, but do know from experience, that if
you don't run a lead subsitute in engines designed for leaded gas, you
will be very lucky if you don't eventually have valve trouble.
Gene Davis
'58 GMC 1/2T
NAPCO
'63 Cessna 182
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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