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BobsV35B(at)aol.com
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 Posted: Sun Mar 18, 2012 12:30 pm Post subject: valve problem |
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Good Afternoon Dennis,
I am afraid we are trying to talk about many things all at the same time.
Fact one. Engines that have high cylinder pressures will need a higher octane fuel. (If we really want to get technical, we can change the delivery system to inject the fuel in a way that will allow higher cylinder pressures to be utilized with lower octane fuel. Things are being done with modern automobile engines to address that problem, but discussion of such procedures are far beyond my current capability.)
If no high octane fuel is available, we can get by with a lower octane fuel by avoiding full throttle operation, but the safer way is to lower the compression ratio.
Any fuel with higher octane will avoid detonation. The octane does not have to be increased by using lead. There are other methods of getting high octane, but those methods cost more than adding lead.
Fact Two. If you get detonation, you will probably burn valves and you may blow the thing up! Even bend rods!
I do not see anywhere that you have shown that leaded fuel burns cooler. What we agree on is that high compression ratios lead to high cylinder pressures and we need a higher octane to safely run at those higher cylinder pressures. Get detonation and the engine will run hotter, but that is NOT due to the fuel inherently burning at a different temperature!
Fact Three. I am not a fan of Ethanol, but if it was all we had, our engines and fuel delivery systems could be redesigned to utilize that fuel.
At the present time, Ethanol has less power available per gallon and the cost is very high. Without subsidies, I doubt if anyone would voluntarily use Ethanol.
Let us please take these problems one at a time so we can easily digest the problems involved.
Happy Skies,
Old Bob
In a message dated 3/18/2012 2:44:51 P.M. Central Daylight Time, dwwilt(at)aol.com writes:
| Quote: | Bob,
If you are running an engine designed to run on 100 octane fuel and you can only get less than that, you will burn the valve seats. Any classic car guy will tell you that. Every old classic car engine that gets rebuilt will have hardened seats installed or the machine shop doesn't understand older engines running on unleaded / lower octane fuel. Especially those with higher compression engines. I could probably get buy without using hardened seats in a 200cid 6 cylinder from the 60's. You must know 100 octane anything burns cooler than 91 or less octane fuel. I should have said that since you can't buy 100 octane unleaded fuel (in most places) that auto fuel is lower octane and burns hotter than 100LL.
Ethanol is horrible for older cars and their fuel lines that have not been changed in a while. After about 4 years, all of my fuel lines began to leak because there is something in there that just makes them deteriorate. Another problem with auto fuel is finding non-ethanol gas. Unless you go to a marina, it is very difficult to find just anywhere. You surely can't use ethanol in a fiberglass tank. Talk to the marine folks about that one. I have fiberglass tanks in my Lightning. I choose to use 100LL. Too hard to find unleaded premium without ethanol and who is to say it may have it anyway since ethanol is standard now for car fuel.
Have a wonderful day,
Dennis
N616DW (Arion Lightning S/N 132)
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Mon Mar 19, 2012 2:46 am Post subject: valve problem |
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Good morning, Bob-
No, I don't have a clue to what the problem was, nor if those
induction hardened (if indeed they were) valve seats cured the
problem. (We had three shifts working the proving grounds those days,
and quite often a problem would come and go before a worker could
such as I was, could return to work and try to track down what was
done. We also would be moved around from project to project, from day
to day, and this really kept us in the dark.)
(Thinking back to those days, we also had a slant-six that was touted
as a "lean-burn" vehicle, and was one of the 3 cars that we drove
from Michigan to Phoenix and eventually on to California for cooling
systems testing.)
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062
Prince prop 64 x 30, P-tip
Electroair direct-fire ignition system
Rotec TBI-40 injection (sleeved to 36mm)
Status: flying with 1237 hrs... (since 3-27-2006)
On Mar 18, 2012, at 9:29 AM, BobsV35B(at)aol.com wrote:
| Quote: | Good Morning Lynn,
Do you recall what the engineers decided was the problem at Chrysler?
When I attended school concerning engine operation, such problems
were noted.
Lead does a good low cost job of controlling the rate of
combustion. Take away the lead and the combustion characteristics
may change in a negative direction. It seems reasonable that
changing the combustion characteristics will affect engine
operations and the change needs to be considered.
In a very general way, take out the lead and you need to lower the
compression ratio.
There are ways of controlling the timing of fuel into the cylinder
that can allow higher compression with unleaded fuel, but such
things are way above my pay grade!
Once again. I am not an engineer, just an interested student of the
results.
I have never found a graduate engineer trained in the field that
felt lead was beneficial to the engine, though the lead was the
cheapest way to eliminate detonation.
I think we can all agree that detonation is a bad thing!
Taking away the lead will certainly change the combustion
characteristics. That we do have to consider when we set up the
engine.
Your experience certainly emphasizes the point that small changes
often have unforeseen results.
Happy Skies,
Old Bob
In a message dated 3/18/2012 6:50:31 A.M. Central Daylight Time,
lynnmatt(at)jps.net writes:
<lynnmatt(at)jps.net>
Good morning Bob-
I haven't spoken with you for a while now...good to hear from you
As to the "cushioning" effect of the lead in leaded gasoline, I offer
the following two anecdotes that I had first-hand knowledge of:
First, I used to work at the Chrysler Proving Grounds as a driver/
mechanic. When the talk of unleaded fuels first appeared, we had a
big-block engine...either a 383 or 413 cu. inch...that we were going
to use as a test vehicle for this fuel. In short order...I don't
recall how long....the engine began to run roughly, and it was
revealed that the valve seats were being "pounded" into the heads.
(The hydraulic valve adjusters compensated for the change in valve
geometry until they ran out of compensation) A few days later a new
set of heads arrived, and they had been "induction hardened"
according to one of the engineers involved in the project. I could
see an area of blue around the valve seats....my memory has faded
enough that I don't recall if all the valve seats were done or only
the exhausts, but it seems like it was only the exhausts.
Cut to about 20 years later (as I recall) and I was living in
California and driving a 1973 Datsun Z, and when California stopped
selling leaded fuel, and I was forced to use it in my Z, the engine
began to run a bit roughly, and I found some valves that were too
tight in their adjustments for clearance. I adjusted accordingly, and
a few weeks later, had to adjust again. And on and on, until I ran
out of adjustment on the rocker arms. Because I needed to keep the Z
running for transportation to work, I got another head from a scrap
yard and dropped it off at the auto machine shop for a valve job and
the installation of hardened seats. To my surprise, the techie called
me and said that this head already had hardened seats installed. That
head is still on my Z and is still running.
So whatever the reason, the leaded fuel did not harm my engine as it
relates to valve operation, but that unleaded stuff sure did a number
on it.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062
Prince prop 64 x 30, P-tip
Electroair direct-fire ignition system
Rotec TBI-40 injection (sleeved to 36mm)
Status: flying with 1236 hrs... (since 3-27-2006)
www.matronics.com/contribution _-
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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