Today's Message Index:
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1. 01:46 AM - Re: Engines-List Digest: 19 Msgs - 08/29/03 (Miles McCallum)
2. 01:48 AM - Re: Lead and exhaust valves (Phil & Michele Miller)
3. 06:25 AM - Re: Re: Engines-List Digest: 19 Msgs - 08/29/03 (Archie)
4. 08:37 AM - Rotax engines are designed to run unleaded (flyseaplane)
5. 09:20 AM - Re: Re: Engines-List Digest: 19 Msgs - 08/29/03 (James R. Cunningham)
6. 02:28 PM - oil, octane and lead (Gary Casey)
7. 05:42 PM - Re: oil, octane and lead (steve korney)
Message 1
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| Subject: | Re: Engines-List Digest: 19 Msgs - 08/29/03 |
--> Engines-List message posted by: "Miles McCallum" <milesm@avnet.co.uk>
>
> >He goes on to say:
> >"Lead does NOT prevent (or cause) "valve recession."
> >
> >I disagree with that.
> >I was there when "regular" gas disappeared, and I saw several vehicles
> >without hardened seats start running like crap in no time - - - and ALL
at
> >the SAME time (running time wise). The only change was unleaded gas. Pull
> >the heads, and the seats are all gone.
> >
> >So, my question is this - - - - - - If lead doesn't protect the valves
and
> >seats, why did the marine engines mentioned in Deakin's article have a
> >problem with the valve seats once the lead was taken away??
> >
> > My Lycoming O-290-D doesn't have hardened seats. I don't run straight
auto
> >gas, out of fear that the exhaust seats will diappear, just like in my
> >pre-70's auto engines. If anyone comes up with a sure-fire way to fix the
> >seat recession problem with unleaded gas, let me know!!
> >
> >Take care all.
> >Linc
> >
>
> I was around when the change happened, as well. I can't quote chapter &
> verse, but if memory serves, the connection between lead & valves wasn't
> lubrication, it had more to do with a 'cushioning' effect between the
> valve & seat. Does this jog anyone else's memory? (What's almost
> universally forgotten are all the sticking valve problems inherent in
> those old auto engines.)
>
> Charlie
>
On the right track here - the TEL both lubricates and cushions the valve
contact face, preventing it from spotwelding itself to the seat: this then
tears hard nodules from the seat, and these act as an abrasive to produce
VSR. Running about 1 tank in 5 of 100LL deposits enough on the seats to
prevent the problem, but you'll have to clean all the **** out of the plugs
after that....
Miles McCallum
Technical editor, Flyer Magazine
www.flyer.co.uk
Message 2
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| Subject: | Lead and exhaust valves |
--> Engines-List message posted by: "Phil & Michele Miller" <millerpg@ps.gen.nz>
Hi, Linc,
I'm just a lurker on this list in order to further educate myself
courtesy of the group. Can't help putting my 2 cent's worth on this one
though. Rotax recommend lead-free mogas in their 912/912S/914 aero
engines. I guess they have hardened valve seats. May be worth your while
checking with your nearest Rotax dealer if you think they can offer any
insight.
BTW, the 912S compression ratio is 10.5:1. Mine runs fine on 96 octane
mogas with no detonation or vapour lock problems but I do have heat
protection on all under-cowl fuel lines
Cheers,
Phil Miller
New Zealand
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com] On Behalf Of
flyseaplane
Subject: Engines-List: Lead and exhaust valves
My Lycoming O-290-D doesn't have hardened seats. I don't run straight
auto gas, out of fear that the exhaust seats will diappear, just like in
my pre-70's auto engines. If anyone comes up with a sure-fire way to fix
the seat recession problem with unleaded gas, let me know!!
Take care all.
Linc
direct advertising on the Matronics Forums.
Message 3
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| Subject: | Re: Engines-List Digest: 19 Msgs - 08/29/03 |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> On the right track here - the TEL both lubricates and cushions the valve
> contact face, preventing it from spotwelding itself to the seat: this then
> tears hard nodules from the seat, and these act as an abrasive to produce
> VSR. Running about 1 tank in 5 of 100LL deposits enough on the seats to
> prevent the problem, but you'll have to clean all the **** out of the
plugs
> after that....
>
> Miles McCallum
> Technical editor, Flyer Magazine
> www.flyer.co.uk
Indeed.
100 LL , (I believe), contains about ten times the amount of lead
that leaded auto fuel once had.
During an interview with Paul Royko, of Aeroshell, he told me
they have already formulated and are continuously working on an
unleaded fuel aviation oil.
He also indicated that it is only a matter of time when this
conversion takes place.
Archie
Archie's Racing Service
Message 4
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| Subject: | Rotax engines are designed to run unleaded |
--> Engines-List message posted by: "flyseaplane" <flyseaplane@netzero.net>
Hi Phil -
The Rotax 4-cycle engines are an entirely new design and engineered to run
on unleaded petrol. Running 100LL through them fouls them up. Best thing is
to run unleaded in the Rotax 912 series.
If Lycoming and Continental would borrow a mere 5% of Rotax technology we
would all be in better shape!!
OH by the way, Dan Ward says he enjoyed visiting with you. Hope you guys got
the whole prop/starting issue figured out.
Take care,
Linc
DO NOT ARCHIVE
Message 5
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| Subject: | Re: Engines-List Digest: 19 Msgs - 08/29/03 |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
You got that right, Miles.
All the best,
Jim Cunningham
Miles McCallum wrote:
> Running about 1 tank in 5 of 100LL deposits enough on the seats to
> prevent the problem, but you'll have to clean all the **** out of the plugs
> after that....
>
> Miles McCallum
> Technical editor, Flyer Magazine
> www.flyer.co.uk
Message 6
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| Subject: | oil, octane and lead |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
Octane: Yes, there are two basic methods of determining octane number -
"Research" and "Motor." These date back maybe 75 years. The motor octane
method runs the test engine at higher temperature and load and therefore
results in a lower number. The difference between the two numbers can give
some idea of the sensitivity of the fuel to combustion chamber surface
temperatures, etc. Motor octane numbers may better reflect the air-cooled
aircraft engine operation than the research method so it would be logical to
use that number (the number on car gas pumps is the average of the two).
Octane number is NOT an indication of the "speed of combustion", but is a
measure of the resistance of the fuel to auto-ignition or detonation. A
combustible mixture of fuel will auto-ignite (explode) as a complex function
of temperature, pressure and time. However, you can create a combination of
these conditions and the fuel will still not ignite instantly as there is
still a time delay, called ignition delay. Much of the time the fuel is
exposed to a temperature/pressure combination that will cause ignition, but
the flame front reaches the fuel before the ignition delay expires. That is
the main reason an engine has a higher octane requirement running on one
spark plug than two. Retarding the ignition timing will usually reduce the
octane requirement because the peak pressure and temperature are reduced
since more of the combustion occurs after TDC. And the important last piece
of fuel to burn is exposed to a reducing pressure since just as it was about
to ignite the piston started going down. Running at a retarded spark will
produce the same power regardless of the octane number of the fuel; Higher
octane fuel will just allow more spark advance to be used before the onset
of detonation.
Oil: Our experience at Mercury Marine was with the early pre-production
502's, which had a serious oil consumption problem. We couldn't run the
engines long enough before pre-ignition, cylinder scoring piston destruction
or other problems to get good data. At high powers the ash build-up on the
spark plugs would become conductive, shorting the plug with the end result
of pre-ignition and engine failure. Switching to aircraft ashless
dispersant oil cured the problem. The reason is that "normal" oil contains
ash, meaning that when it burns it creates an ash. Ash can be a number of
compounds, but it is basically sand or rock; the oxide of a metal. This ash
is very abrasive and can cause all sorts of problems including deposit
buildup on the spark plug insulator that can become conductive. Ashless
means that the oil has ash-producing materials removed and hence when
burning produces little or no ash. Car engines don't need ashless oil
because they typically don't burn enough oil to make it worth the extra
cost. An aircraft engine that doesn't burn much oil could also probably use
an automotive oil without problem.
Oil is cheap? Doesn't seem like it to me. 8 quarts at $5 plus a $15 filter
used in 25 hours seems like $2.20 an hour, not bank-breaking, but not
trivial. Many years at GM we did about a million miles of testing at
different oil change intervals. After all that the conclusion was you could
double or triple the oil change interval without any
statistically-significant change in engine durability. At the time I had
never heard of any GM company car (except test cars on specific regimens)
that ever had its oil changed. Aircraft engines, though, are different
because of lead and blowby contamination. Assuming the existence of a
full-flow filter I believe the oil change intervals specified by the OEM's
are very conservative. My C-TR182 manual specified oil changes every 100
hours and filter changes every 50. I changed both at 50 simply because I
had the cowl off and might as well. I have typically started thinking about
changing the oil at 50 hours, but I don't like going over 75. In other
words if I am on a 20-hour cross-country trip I would think nothing of
leaving home with 45 hours on the oil and not changing it till I got back.
Four engines, all Lycoming parallel-valve designs, ran over TBO every time
like that. If you change oil every 25 hours, give it to me - I'll put it in
my engine and run it another 25. MY experience certainly is not extensive
enough to be statistically valid, but it doesn't contradict the normal
experience.
The term "dispersant" is not related to the word "ashless" in the oil
description. It says that there are detergents in the oil that are there to
maintain dirt (and lead oxide) particles in suspension. For example,
automotive oil is dispersant but not ashless.
Lead: I was at GM when lead-free fuel became available, and yes there were
valve seat wear problems without lead. In those days most all U.S.-built
engines used cast iron of questionable quality for cylinder heads and the
seats were machined right in the heads. We found that if we locally
hardened the seat area of the head the wear problem essentially went away.
The wear was a dramatic function of temperature and that's why a car engine
might get by while a truck or marine engine probably wouldn't. I didn't
know any aircraft engines used soft valve seat materials, but I would worry
about using lead-free fuel if that were the case. A very small amount of
lead goes a long way, and even if you put in leaded fuel every few tanks
that would probably be adequate. It doesn't have to be constantly
available. We found that all other durability issues were much reduced with
lead-free fuels. Spark plugs and exhaust systems would last almost forever.
Valve sticking issues were reduced.
<<Consider the engines running on Propane or Natural gas.
Ever wonder what they use?>>
All these engines that were purpose-built used hardened exhaust valve seats
specifically because of the wear issue. Before all engines had these most
of the automotive-based engines were specially built with hardened seats for
LPG or CNG use. People that ran LPG conversions in their vehicles were
advised to occasionally switch to gasoline.
Gary Casey
Message 7
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| Subject: | Re: oil, octane and lead |
--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
Thanks Gary...
That's the best discription Iv'e heard yet and makes a lot of sense too...
Best... Steve
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