Hi Walter !
What you are doing is very wise ! The old Lycomings & Continentals
don't have modern metallurgy anywhere - and the valve seats are particularly
vulnerable. This is where the lead comes in - it lubes the seats and prevents
the valves from spot-welding onto the seat ! I've seen several valves with
big chunks of seat stuck to them !!!
The O-320 (and most old engines) were designed for 80/87 Avgas -
100 LL has FOUR TIMES as much lead as 80/87 !! That's why we get
lead fouling on the plugs - and leaning at idle can help, if you're careful,
AND don't forget to go rich for takeoff !!
Old engines have a considerable amount of lead stored in the pores of
the metal, and it leaches out over time when you run mogas (unleaded),
providing some lubrication. This lead needs to be replenished by running
the odd (say -- 1 in 4 ) tankful of 100LL - either that, or you should add
some AVP or similar valve lubricant. Your alternating fuel usage should
serve you well !
I always ran 100LL in one tank, and Shell Bronze in the other - apparently
there are good reasons NOT to mix fuel types . They don't really mix evenly,
the mogas attracts more water, and can gum up, and there may be interactions
between additives. (This from an old pro in the fuel business ....)
(Shell - because they were the ONLY company that DIDN'T add alcohol !)
I know from experience that Mogas has changed drastically over the last
10 years - it doesn't have nearly the 'shelf life' it did have, and seems to
lose effectiveness much quicker. Also seems to have a larger proportion of
'oily' residue - likely things to satisfy the EPA, more than improve operation
of the engine. In the winter, they blend it to be much more volitile, for
easy starting, and add more alcohol to grab water, making it less desireable
for aircraft use. All good reasons to use 100LL in winter !
The savings in fuel costs is not enough to cover the costs of new cylinders
needed if a valve sticks - or much more damage if the engine quits !! The odd
tak of 100LL will help avoid this problem.
Also - those who are running Mogas - if you don't already, you can claim
a rebate of the 'Road Tax' included in the mogas price in most areas. In
Ontario, all you need is copies of your fuel receipts (in case they ask), and
send in an application with a photocopy of your log book pages. As long as
the fuel used matches (approx.) the hours flown, you get about 12 cents
a liter (!!!) as a refund !! Definitely worth asking for !
.......bobp
-------------------------------orig.-------------------------
On Thursday 16 December 2004 12:25 pm, WALTER KLATT wrote:
My main concern about mogas is the possibility of gumming, and I have had
that happen in the past with boats and motorcyles that weren't used for a
while. In my case, because I use that fuel flow sensor, I don't like to
take the chance of that thing plugging or being a problem. So during the
winter, or when I might not fly as frequently, that's when I run avgas.
Also, on trips, as Bruce mentions, you often don't have a choice, so my
plane still get its fair share of avgas in a year. I do stay away from
alcohol fuels, though.
Walter
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